UNIT III

Introduction

Light by definition connotes Electromagnetic radiation that has a wavelength in the range from about 4,000 (violet) to about 7,700 (red) angstroms and may be perceived by the normal unaided human eye. In fact in the prehistoric days, all human activities were coordinated with Sunrise and Sunset. Today, in principle activities are carried out round the clock. All this is made possible because of Artificial Lighting systems. The lighting systems comprise of a source employinganyphysicalphenomenonamongIncandescence,Electrolumniescenceor Flourescence. Some control scheme and a Luminaire. In fact all this has lead to a class of professionals called Lighting Engineers or Illumination Engineers. Unlike other group of professionals they need to be adept at not only at exact sciences of Maths, Physics, Chemistry; but be wary of Physiology and Psychology of users (like a medical professional); have good aesthetic sense and economically utilize resources (like an architect video Fig. 1). Efficacy of these systems is talked in terms of Illuminance per Watt of energy consumed. Efforts are on to reduce energy conmsumption yet have efficient Illumination to enhance productivity. Need less

to mention that all these sources employ electrical energy. Trend these days is to employ, modern electronic controls together with energy efficient lamps. These aspects are borne in mind, right from the planning stage of a building. As electrical energy is being used for the purpose, it becomes important for Illuminating Engineer to come up with an integrated system for the complete electrical system of a building.

Medicine

PhysiologyPsychology

IlluminationEngineering

Architecture

Math Chemistry Physics

Economics

Usefulness to Humanity

Art(Aesthetic point)

Fig. 1 Professions-sciences-usefulness relationship.

1. Necessity of Illumination

Humans depend on Light for all activities. Light is a natural phenomenon, very vital for existence, which is taken for granted. In fact, Life involves day night cycles beginning with sunrise and ending with sunset. Pre-historic man had activities limited only to day time. Artificial light enables extended activity period employing in an planned optimized manner, minimizing the resources.

Vision is the most important sense accounting for 80% information acquisition for humans. Information may be acquired through sun/moon light (direct/ reflected) or by using artificial light (closest to natural light). Before we go any further, it is worth looking at Teichmullers definition for lighting. We say the lighting is good, when our eyes can clearly and pleasantly perceive the things around us. Therefore Artificial light should be Functional and pleasant both Physiologically and Psychologically. This is often achieved employing multiple sources. It must be borne in mind that the sources should be economic and energy efficient. As all of us are aware, all sources today employ electrical energy.

Electrical energy is supplied as a.c. (alternating current) or d.c. (direct current). Usually electric power supply is a.c. in nature, either single phase or three phase. It must be borne that close circuit is a must for current flow. As it is well known losses exist in all electrical circuits or lines.

By definition Losses = i2 R, where i = line current in A,R = line resistance in longer the line higher the resistance and higher level.Thus for a particular power level current decreases with increase in voltage i.e.p = v x i (instantaneous power). Hence, losses are minimized by supplying at higher voltages. Normal sources of electrical energy are either hydro or thermal (coal based or nuclear). Usually power stations are located very far from load centers. Therefore, power is transmitted at high voltages.

It may be mentioned that, standard levels of power transmission being 132, 220, 340, 400, 735,765, 1000 kV ac. HVDC or High Voltage Direct Current transmission is also fast catching up as an alternative.Fig.2 shows a single line diagram of a typical Power System with all its components.

~

Generator11/33 kV

Xmission line132/220/400 kV

Distribution line66/33/11kV

400V

Fig. 2 Typical Power System

We know that load is always unbalanced for a practical 3-phase system. Fig 3 shows the waveform of a 400 V 50 Hz a.c supply. Here, 400 V, 3 phase, 50 Hz connotes that supply is three phase a.c. at a frequency of 50 Hz with a line to line voltage of 400 V rms, which translates to 564 V peak value.

V

564

2

1ms ms t

Fig. 3 Waveform of 400V, 50Hz a.c supply

In view of the fact that artificial Illumination employs electrical energy in a.c form, next, we address each fundamentals of a.c generation.

Version 2 EE IIT, Kharagpur28

Physical Processes Employed in the artificial sources

1. IncandescenceThermo luminescence is by definition radiation at high temperature. The sources employingthis process are Incandescent Lamp, Gas Lamp, (flames and in oil Lamps and wax candles). They lead to a continuous spectrum of radiation.

2. Luminescence Luminescence Electro luminescence by definition Chemical or Electrical Action on gases or vapour radiation. Here color of radiation depends on the material employed. Usually this process leads to Line or Band Spectrum.

3. FluorescenceFluorescence is a process in which radiation is absorbed at one wavelength and radiated atanother wavelength eg: UV impinging on Uranium Fluorescent oils. This re radiation makes the light radiated visible.

4. PhosphorescencePhosphorescence is a process when energy is absorbed at some time and radiated later as glow. Examples of this process are Luminous paints that contain calcium sulfide that lead to Phosphorescence. They produce light Radiation after exposure to light.In practice good efficient lighting is obtained by combining Luminescence and Fluorescence. Fluorescent lamp is Luminescent source of low luminous value activating Fluorescent surfaces which lead to visible radiation. Here intensity depends on gas or vapor involved and phosphor material. However, the temperature of the material play a role in radiation. That is taken up next

Laws of Illumination

The original standard of light was Wax Candle, which is highly unreliable. It was replaced by a Vaporized Pentane Lamp. This is equal to10 original Candles. In the year 1909, Incandescent Lamp was taken as standard by comparison with a Pentane Lamp. Thing to be kept in mind is Primary Standard should be reproducible.It was in1948, Luminous Intensity; based on Luminance (objective brightness) of a small aperture due to Light from a Radiator maintained at1773c i.e. Solidification temperature of platinum was adopted as Standard. It consists of:

1. Radiator Fused Thoria Thorium Oxide. 45mm long internal dia of 2.5mm. Packed with Fused Thoria Powder at the bottom.

2. Supported Vertically Pure Platinum in a Fused thoria crucible with a small aperture of1.5mm in a large refractory container.3. Platinum melted by a High Frequency Eddy current.Luminance = 589000 Candles /m2 600 000 units

The standard is shown in Fig.1.

Transparent

Common unit of light intensity is candela. It is Luminous intensity in the Perpendicular direction of a surface, 1 / 600,000 of a black body at temperature of solidification or Freezing of Platinum under Standard Atmospheric pressure. It is abbreviated as Cd. It is indicative of Light Radiating Capacity of a source of Lamp.

Fig. 2 Light flux

Consider a transparent sphere of radius 1m shown in Fig.2. If we place a 1 Cd source at the centre then light flux coming out through an area of 1m2 over 1 steradian solid angle will be 1 lumen.

Thus Luminous Intensity over 1 Str. by 1, Cd, we call it 1 lumen 1 lm. Basic unit of LightFlux. Total Flux = 4 lumens, out of the sphere in Fig 2.If the Solid Angle be d and Luminous Intensity I Cd at the center then Luminous flux in d =d = I d lm.

I = d Cd d

Yet another important unit is MSLI. It means Mean Spherical Luminous Intensity. Average value of Luminous Intensity in all directions. Therefore for the case in Fig 2. = I 4 lumens

Now we define Luminous intensity on a surface. It is known as Illuminance. It is Luminous Flux per unit area or lumens per sq m. = lumen / m2 = lm / m2 = lux (lx).

Fig. 3 Definition of Illuminance.

Frechners law

Weber in 1830 found that I Stimulus (Intensity) produces dI Least perceptible increment affecting sense organs. Then the ratio

dI = Constant " Under fixed 1) FatigueI2) Attention and3) Expectation.Thus we have sensitivity given by the equation

S = C log

I""""(2)Io

Here I0 is the threshold intensity. This is known as Frechners Law. The same percentage change in stimulus Calculated from the least amount perceptible. Gives same change in sensation. Sensation produced by optic nerves have logarithmic dependence or relationship to Light Radiation producing the sensation.

Inverse Square Law

Intensity of Illumination produced by a point source varies inversely as square of the distance from the source. It is given by the equation and as shown in Fig. 3E= I """"(3) D2Where I is

Lamberts Cosine Law of Incidence

E = I cos """(4) D2

This tells us the variation of Illuminance on arbitrary surface inclined at an angle of . As shown in Fig 4.

Fig. 4 Lamberts Cosine Law of Emission

I = I cos """"(5)

Fig. 5 Typical Lighting Scheme

Fig. 5 shows a lamp placed at A, bm above the floor.For this scheme Fig 6. shows the variation of Illuminance on the floor. It is well known that Illuminance is maximum under the lamp at B.

Fig. 6 Variation of Illuminance

Illuminance at B = LI in direction ABb2

Illuminance at C = LI in direction ACAC 2

= LI in direction AB Cos(b2 + d2 )

= LI in direction AB b3(b2 + d2 ) 2

Cos =

bb2 + d2

Illuminance at C = Illuminance at Bx Cos3

3=Illuminance at B[1+ (d b)2] 2Next is to measure the candle power of the lamp. Typical measurement can be done using a photometric bench shown in Fig. 7 where IS represents standard lamp. IX represents test lamp. There is a screen at the centre called photometer head, adjusted for equal brightness on either side. Applying inverse law one can arrive at the value of IX.

This lesson introduced the primary standard and other terminology related to measurement of light flux.

Fig. 7 Photometric Bench

Photometry

Primary Standard was defined in an earlier lecture based on the brightness of a body (i.e. black body) maintained at Freezing Temperature of platinum. Unit of Luminous Intensity abbreviated as is candela cd(z). Light Flux hence emanating from a point source in all directions isIlluminance - lumens and is termed msli is the light flux incident on a task surface in lumensper unit area and is called lux. Comparison with a standard. Normally Primary standards are kept in standards Laboratories. Usually Incandescent Lamp Compared with a Primary standard is used as a Laboratory Standard. The test source / lamp is compared With the Laboratory Standard. However, Incandescent Lamp not suitable beyond 50 100 hours Standardization of Lamp is by voltage rating Current rating and wattage.

These measurements comprise photometry. They employ a Photometric Bench with a photometric head which is an opaque screen. These measurements involve compassing the test lamp with standard lamp

a. by varying the position of comparison lamp (standard Lamp) Is b. by varying the position of the test lamp ITc. by varying the position of the screen

Measurement is complete when the bench is balanced. It is balanced when two sides of the screen are equally bright [in a Dark Room] as shown in Fig. 1.

Photometric Bench

I I T 2

s =S2T 2

IT = Is S2

Fig. 1 Photometric Bench

Measurements may be made on Illumination meter or Lux meter also in this instead of the screen adjust the meter to get the same reading on photometric bench. Fig 2. shows a method where distance is varied to get the same reading on the meter.

Fig. 2 Use of Lux meter on Photometric Bench

Alternatively, the distance on the bench may be kept constant and readings on the meter are noted.

Fig. 3 Photometric Bench with Lux meter at a Constant Distance

Then the intensity of the test Lamp is given by the relation

I = I

Reading with Test Lamp

(i)

T s Reading with Standard Lamp

R 2IT = Is

R1

(ii)

Fig. 4 Integrating Photometer

Fig 4 shows a typical photo meter. It has a standard point source L of Light at the centre of a opaque sphere. It has an opening W where a photo cell is placed that receives diffused light from the source. Window W is shielded by diffusing screen C from direct light. Reading on the micrometer is first taken with a standard Lamp and later with the test Lamp. Then we have

msli of test Lamp=

reading with test lamp

(iii)

msli of standard Lampreading with standard lamp

from this, one can obtain light flux output of the test lamp by multiplying msli with 4.

Fig. 5 shows the photocell employed in a photometer. In a photocell sensitive element S is selenium coated in the form of a thin layer on a steel plate P. This is in turn covered with a thin layer of Metal M on which is a collection ring R.

Fig. 5 Photovoltaic cell

Sensitive element is a semi-conductor that releases electrons upon exposure to light. Selenium and Cuprous oxide are most suitable semi-conductor materials. Steel Plate P coated with thinlayer of Selenium at 200c and annealed at 80c Producing crystalline form. It is in turn coatedby a thin transparent film of metal M with a collection ring R of metal.

Fig. 6 Top view of a photo cell

B is the barrier Layer Upon exposure to light light enters through M releases electrons from metallic Selenium. They cross barrier B to M and are collected through R and P Current indicated by (A) is proportional to Illuminance. Often (A) is a micro ammeter calibrated in lm.

The next aspect of photometry is to look at the luminance curves of the Lamps. Here comes the role of Luminaries. Luminaries primarily provide the physical support to the Lamps. They may be directing, globes, reflecting or refracting. They could be supported on the walls using wall branects. They may be portable units on pole mounted in case of street Light. In all cares we need light distribution curves. Light distribution curves are curves giving Variation of Luminous intensity with angle of emission in a Horizontal plane i.e. Polar angle Azimuth or Vertical plane, passing though centre.

Fig 7 shows a typical Polar Luminance distribution curve of a point source of Light. From a Polar Curve in order to arrive at msli of the lamp a Rousseau diagram is constructed. Fig 8 shows such a construction.

Fig.7 A typical Polar Luminance distribution diagram

Fig. 8 Rousseau Diagram

Consider the Polar curve A for the typical lamp with O as centre of the Lamp Draw a semicircle of convenient radius OB = OC Insert no. of radii. From the top of there radial segments. From the tip of the radial segments draw horizontal lines extended to cut the vertical line to scale depending on length of Radic. Then the average width of the curve DP Q R S F is msli.

Luminaire

They Provide Support and electrical connection to the lamp. They are used to control and direct the light and distribute as required. They help to keep the operating temperature within prescribed limits. Using Rousseau diagram, graphical techniques are employed to obtain the MSLI. They should be easy to install and maintain and have a pleasing appearance. They are expected to b economically viable. Thus Requirements for good luminaries may be listed as

i.to provide support & electrical connection to the lamp ii.to control, direct & distribute light as requirediii.to keep operating temp. within prescribed limits iv.should be easy to install & maintainv.should have aesthetically pleasing appearance and vi.be economically viable

In them Lens & prisms can be used for focusing the light one has to keep in mind Depreciation which is often used as Maintenance factor varies from 0.85 0.6. This lesson had a look at the ways of measuring light output of a Lamp. They consisted using photometric bench, either by comparison or reading on an illumination meter. Luminaries which form integral part of Illumination system are characterized by polar luminance curves. Way to assess their luminance has also been discussed.

Incandescent Lamps

Natural Illumination due to sun which is 93 million miles away and 865,000 miles in dia, and has temperature > 6000c, leads to 2.3 1027 cd. Luminance. Moon, 240,000 miles away and 2160 miles dia, is said to have I 1.0 1027 cd. In order to provide artificial Illumination one of the following Physical Properties is employed:Incandescence depending on thermo luminescence,Luminescence depending on electrical discharge in a gas or vaporFluorescence depending on radiation of visible light by absorbing ultra violet light andPhosphorescence involving radiation at a latter point in time.

Incandescent Lamps

Incandescent Lamps were first invented by Edison in 1879. They employed Carbonized Paper asFilament. It was Fragile. Later it was improved by coating with a Hydrocarbon. In 1893Cellulose Filament was developed from absorbent cotton dissolved in ZnCl. Normally Filament is mounted in a glass bulb and maintained in vacuum (type B) getsheated upon Passage of current and typically radiating 3.3 lm / W. They are called Type B lamps. In 1905, Metallizing by heating Carbon filament at high temperature in an Electric furnace efficiency improved to 4.0 lm/W. In Europe Osmium a Rare & expensive Fragile filaments were employed with 5 lm/W radiation. It was soon, replaced by Tantalum a Ductile material (1906 - 1913) by crystallizing by application of ac leading to 5 lm/W radiation. In 1907 Tungsten Filaments entered with 7 lm / W radiation. Finely divided Tungsten Powder is mixed with a binder and squirted through a die. In1911 Coolidge developed Tungsten in ductile form which could result in a Continuous uniform Filament. It was Rugged and had very high efficiency. Langmuir introduced use of inert gases and improved the radiation efficiency (1913). They ware called type C.

Fig. 1 Incandescent Lamps

Fig. 1 shows a typical Incandescent Lamp. It has filament made of Tungsten of S. G. 18.81 before drawing, 19.3 20.2 after drawing with a high mp of 3655K. (Osmium with a mp of2972K & Tantalum with a mp of 3172K). Were other materials Theoretically 52 lm / W radiation is possible at m.p but Practically, Highest radiation of 35.8 lm / W is achievable. They are available from 250W Flood Light with a life up 3 hours to 1500 W (at 115 V) of 1000 hr liferadiating 22 lm / W. Smaller lamps being 6 W(at 115 V) with a 1500 hr life radiating 6 lm / W. Smallest Lamp being used in Surgical Instruments of 0.17 W of Grain of wheat radiation 0.35 lm. Largest Lamp being 50,000 W; 1,600,000 Lumens. Equivalent to 1000 - 100 W Lamps. Inert Gases are introduced in the Glass envelope to decrease the vaporizations of Tungsten. The gases Nitrogen and Argon are most suitable. Conduction Losses in a gas are proportional to velocity of gas molecules. Velocity is inversely proportional to square Root of atomic weight. Argon with atomic weight of 39.8 and Nitrogen with atomic weight 28.0 are most suitable. Ionization Potential of Argon is low. Hence a mixture of Argon and Nitrogen in the ratio of 85% Argon 15% Nitrogen are employed. Concentrate the filament over a small region. To adopt tightly wound helical coil.

Fig. 2 Blackening of Glass Bulb

Fig. 2: shows darkening of Glass bulbs due to vaporization of Tungsten. Hence the lamps are called either

Type B Vacuum< 40 W rating orType C Gas> 40 W using Inert gases

During operation Filament evaporates and Tungsten particles deposit on the interior of Bulb in a Vacuum Lamp. Tungsten Filament cross section of the Filament decides the current Rating and varies as square of dia. The radiation surface varies as dia. With decrease in operating voltage for the same wattage filament becomes larger. If a lamp of 40W were to operate at 115 V and has a cross section C S1 , it becomes C S 2 at 220 V then C S1 > C S 2 .

Fig. 3 Voltage vs Efficiency

Fig. 3 shows variations of voltage with luminous efficiency for 40 W and 100W lamps. As may be observed for both the lamps variation in luminous efficacy between 200 240V is very little. It implies that small variations in voltage do not effect the light efficiency. Where as in the 110V region variation is significant though one gets higher efficacy compared to 220V region.

Fig. 4 Performance Curves

Fig. 5 Characteristics with change in voltage

Figures 4 and 5 show the performance of Incandescent Lamps. As may be seen from Fig. 4 both luminous efficacy lm/W and light flux lumeses reduce to 20% of Virgin values. Fig 5 shows the effect of variation of voltage from rated value. From this it may be said that although light output may reduce marginally when voltage reduces, one can get near 90% performance at about 95% rated voltage. Fig 6 shows the survival rate. More than 81% survive 80% stated life. Only 30% survive beyond 100% stated life.

Fig. 6 Survival Rate

Filament characteristics depend on Filament Length, Diameter, Coil Spacing, Lead wires, No. of Supports, Method of mounting, Properties of Gas, Gas Pressure, Bulb Size and Shape of the Bulb.

The lamp is said to be most economical for the intended Service, if uniform radiation is there at stated wattage with guaranteed efficiency and Life Rating. Lamp characteristics may be quantified interest of

Watts W, Lumens F, Lumens per watt E, Life L, and Volts V

Equations (1) to (4) give the characteristics. They all show dependence on exponents a, b, c, d, e, f, g and h.Table I shows the typical values for Gas Lamps and Vacuum Lamp

aw = ( v )( ) 1W V

VW=F=f( v )b

( w )c

( 2) ?

Typical cal values of Exponents

VfeE = ( v )d = ( F )e (3)

l = ( V )f

= ( F )g = ( E )h ( 4)

Lvfe

Table I: Typical Constants

abcdefgh

G

A1.543.382.191.840.54413.13.867.1

S

V

A

C1.583.512.221.930.54013.53.857.0

U

U

M

This lecture covered the characteristics of Incandescent Lamps. One important specifications of any light source is power consumed in watts. Any lamp is guaranteed to give radiation at stated efficiency, if operated around rated voltage.

Discharge Lamps

Incandescence was employed in Tungsten Filament lamps. Halides were employed to reduce blackening of the bulb. Lumniescence and Fluorescence increase efficiency far beyond incandescence. Discharge of electricity through a tube containing a conducting medium leading to electron Flow is employed in Lumniescence. This calls for an abundant supply of electrons.

Electron Emission

Electron emission is a process by which abundant supply of electrons is obtained. Electric Field Emission is employed in Cold cathode Lamps. Electrons are pulled out by application of High Potential. Thermionic Emission is employed in Hot cathode Lamps. Electrons are emitted even at a low voltage by heating. Barium / strontium oxide on a base of iron or Tungsten is used as Cathode.Photo electric Emission: Striking with Light Radiation of Photons, emission is achieved. Thus gas / vapor made Luminous by an electric discharge. Color / intensity of light are dependent on Gas / vapor employed. Intensity is proportional to the current. Commonly used gases are Neon, Mercury and Sodium. Cold Cathode needs large energy consumption at the cathode with decreased efficiency. This may lead to disintegration of cathode with high velocity positive ions due to large Potential drop at the cathode. Blackening of cathode does occur. They have Long Discharge Tubes with Low voltage Lamps. Mercury Vapor Lamps give light of Bluish Green, deficient in red rays. In this case color rendering (CRI) improves at high Pressures. Considerable distortion in colors occurs.Mercury oxide coated Cathodes (Electrodes) are employed. In a typical discharge lamp coated tungsten wire electrodes with Strontium Oxide or Barium oxide coating are located at the opposite ends of a glass tube.

Mercury Vapor Lamp

Arc is a Constant Current Phenomenon. The starting electrodes are connected to lower electrode through a resistance (R). Arc tube contains Mercury at the desired vapor pressure. Pure Argon initiates arc prior to vaporization as pressure is increased Radiation moves into visible spectrum. Standard Rating are 100,250, 3000 W with a typical illumination of 35 lm / W. Arc initiation takes place at 20V at about 5A. Argon arc lasts for 2 min with a bluish Glow. At about 137 V, 3.2 A Mercury vaporizes and takes over. Run up time or arc initiation time is up to 30 minutes. Lowest run up time is around 2 minutes. Ballast is a reactor in series that limits the current. Typical Power factor 0.65 0.7 capacitors added across the Lamp improve power factor to 0.94.

These lamps are suitable for Factory Lighting, Exterior Lighting / Flood Lighting and Street Lighting. They need 5 min of cooling before restarting. It is found that Combination Lamps UV + Visible Light termed SUN Lamps with 3 min of Run up time and 5 min for restarting are more useful.They give out a band spectrum.Mercury Radiates around 320 400 nm. Remember 365 nm is in the U.V. region.

Sodium Vapor Lamp

It is similar to High Pressure Mercury Vapor Lamp. It is in a hermetically sealed Glass tube with Sodium vapor. Electrodes are elliptical foil of Molybdenum and Coiled Barium oxide coated Tungsten. In one half cycle, Tungsten at the top acts as cathode, Molybdenum at the bottom acts as anode. Other Half cycle electrodes are reversed. Pure metallic sodium does not initiate arc. It needs a starting gas. Neon acts as a starter. This requires preheating, heaters are provided with in the Lamp. The Lamp glows with Red Color (Neon vapor), Orange yellow arc (sodium vapor arc). Leads to a line spectrum of radiation.

Figs. 3 to 7 show the Radiation spectrum for various sources along with curves for human eye sensitivity. In each curve the hatched region indicates, theoretically possible radiation energy in the visible region.It may be observed that incandescent lamp has maximum energy in the visible range and has a continuous spectrum.

Fluorescent Lamp

Employs transformation of UV radiation due to low pressure mercury vapor. Luminescent Powder in tubular vapor Lamps Enhances brilliancy of light.Radiation from Low Pressure Mercury Vapor (which is in UV region) is impinged on Luminescent Materials and re radiated at longer wavelengths of visible spectrum. In a Glass Tube small drop of Mercury and small amount of Argon gas are placed for initiation of discharge. Pressure, voltage and current are so adjusted that 253.7 nm line is excited. This re-radiates at longer wavelength. Typically a 40W lamp requires 2-3g of phosphors. Maximum sensitivity is around 250 260 nm. Various types of Fluorescent Lamps are:1. Day Light Fluorescent Lamps- Average Noon Day Light. 6500k suitable where demands are not exacting2. Standard white Light - 3500k general Lighting.3. 4500k white Lamp between std. white Light & Day Light Lamp.4. Soft white Lamp Pinker Light. 25% lower light output than Std. white Lamp suitable for Residential lighting and Restaurants.

Dimension and Voltage depend on Luminous Efficacy, Brightness, Lumen Output and Lumen Maintenance. Reliable Starting is achieved by having preheated cathodes / hot cathode. Half the open circuit voltage should be used by the Lamp and the other half by the ballast. Lamp Voltage decides the arc length, bulb diameter and lamp current. Hot Cathode lamps operate at lower voltage < cold Cathode lamps. Typically cold cathodes have 70-100V drop at the cathode.

Figure1 shows the schematic of a typical Fluorescent lamp. In a normal lamp the ratio of open circuit voltage to lamp voltage drop is 2 where as in an instant start lamp it is around 4.Figure2 shows the radiation sensitivity of various phosphors.As may be observed, the peak sensitivity at 253.7 nm is for Zinc Beryllium Sulphate. Table 2 lists various phosphor properties. For each material emitted color after fluorescence, range of emission, peak emission wavelength and peak sensitivity are listed. It may be observed that Zinc Beryllium Silicate has peak emission coinciding with peak eye sensitivity. Hence this is the most commonly employed phosphor.

Version 2 EE IIT, Kharagpur9Table 2 Characteristics of Fluorescent Chemicals

PhosphorsColorExcitingRang nmSensitivityPeak nmEmittedRange nmEmittedPeak nm

CalciumTungstateBlue220-300272310-700440

MagnesiumTungstateBlue white220-320285360-720480

Zinc. SiliCateGreen220-296253.7460-640525

Zinc Beryllium silicateYellow white220-300253.7480-750595

Cadmium SilicateYellowPink220-300240480-740595

Cadmium BoratePink220-360250520-750615

Illumination Systems

It is time we looked at an illumination system as a whole.These systems tend to produce radiation close to natural radiation. They employ artificial sources. These sources obeyLaws of Illumination. The quantification is done through Photometry. Thus an Illumination system consists of Lamp which may be Incandescent lamp, Discharge lamp or Fluorescent lamp along with control gear placed in a suitable luminaire.

Luminaries

Luminaire or Luminaries provide support and electrical connection to Lamp or Lamps within it. They control, distribute and direct the Light on to the object. They ensure that lamps are operated in a way such that operating temperature is kept within prescribed limits. They should be easy to install and maintain, aesthetically pleasant and economically viable. Systems may be commercial or general. Usually Fluorescent Lamps with one or more at a preferred mounting height less than5 6 m are used for general lamps. Fluorescent Lamp may be Batten Fully exposed or Multi lamp type. Ventilated-Reflectors with Mirrors optics are used. Difference lies in control of Luminous Intensity, Luminous distribution, No. of Lamps. One may recall that for a

Point source of radiation 1 d2

(e.g one can recall that Incandescent Lamp),

Line source of radiation 1 d

(e.g. Tube Lights), and

Plane Source of Radiation independent of distance (Ideal situation).

Hered is the distance to the source of light. Designer aims in locating Lamps in this fashion. Reflectors help in controlling and directing the light. Louvres-opening with slanted Slates are often employed. Fins / vanes are provided to ventilate. Batten mounted lamps amounts to no control. Most systems have enameled reflectors. Improved ones have Mirror reflectors. Additional control obtained through louvre shields and opalescent shades. Reflectors help direct in a desired solid angle. Louvres may have Square Mesh Box type Luminaries or Diamond Mesh or Lamellae -Thin Plate Layer type.

Fig 1 shows a typical luminaire with reflector and louver. The luminaries may be recessed in the ceiling, mounted on the walls (or a surface) or take box shape as shown in Fig 2. They are suspended at times.

Efficiency of Luminaries is expressed in terms of Light Output Ratio LOR LOR =light output with luminaries individual light output(w/o luminaries)

This includes both downward as well as upward light. Down ward light is important from the utilization point of view. Hence, DLOR is crucial. Up ward light illuminates indirectly by reflection. With Mirror Reflectors, LOR goes up and Glare comes into Consideration.

Industrial Luminaries

Coming to industrial areas if in the Interior-up to 6m Fluorescent Lamp with matt white reflector are employed. In High bays beyond 6m Discharge Lamps with Mirror Reflectors are employed. Luminaries in Hazardous Areas are specially deigned. They are encapsulated in boxes made of steel or cast iron exterior housing to avoid any explosion, sturdy resisting pressure.

Categories of Explosive Areas

In this respect explosives are as are categorized as

Zone 0 Explosive all the time, Zone 1 Normally Explosive and Zone 2 Explosive Abnormally.

Here moisture & dust are taken care by Gasketted Luminnaires Completely sealed eg: in a Shower or a Laundry. Emergency Lighting is required when normal lighting fails. Escape Lighting sufficient for evacuation typically 1 10 lx. Safety Lighting 5% normal Lighting is provided in Potentially Hazardous areas. Stand by power supply required for activation of vital implements. A permanent, separate, self supporting Power system which is reliable and mains rechargeable batteries in each Luminnaire are providedNon Permanent - Auto Switching - Emergency Generator - Battery Supply is also used.

Road Lighting

Conventionally by they are arranged in a column, mounted on a wall or suspended by a span wire. Plane of Symmetry being in vertical plane perpendicular to the axis of the road along the road. Catenary suspended from a catenary cable parallel to the axis of road. Plane of symmetry parallel to the axis of road. They employ Corrosion Resistant sturdy materials and are usually closed.

Flood Lights

Rain Proof Lamp holder with wide / narrow beam Reflectors are used for flood light. They are usually High wattage Incandescent Lamps, Halogen Lamps, High Pressure Mercury Vapor Lamp or Low / high Pressure Sodium Lamp.

Spot lights / down lights are usually used with Screens, Reflectors, Filters, Colored envelope andClosed Lamps.

Down lights are Spot lights when suspended.

This lesson has had a look at the components of an Illumination system under various scenarios.

As already brought out the components of an Illumination system are Lamp, the Radiation Source, Luminaire that directs and controls the light flux. Control Gear is the accessory that helps in controlling the requisite amount of flux on the work plane. Now we take a look at the accessories involved. First of these is Ballast. In a discharge lamp a series impedance to limit the current is required. If the current is allowed to increase there can be explosion of the lamp. This takes the form in a.c. as Inductance-w/o undue loss of power. This is called Ballast. It should have high power factor for economic use of the supply and should generate minimum harmonics. It should offer high impedance to audio frequencies.It should suppress-Electromagnetic interference (Radio interference-TV interference). It is essentially, a reactor of a wound coil on a magnetic core often called Choke and is in series with the lamp. Typical power factor is 0.5 Lag. Power factor is improved by having a capacitor connected across input lines.

Fig 1 shows the connection for a discharge lamp employing a ballast formed by a reactor commonly known as choke. Fig 2 shows how the capacitor may be connected to improve the power factor. As may be seen the capacitor is placed in shunt. At times a lead circuit may result by placing a capacitor in series as shown in Fig 3. However, when a illumination system employing two lamps is used power factor may be improved by having one with a lead circuit and other with a lag circuit as shown in Fig. 4. Next important accessory is a starter that initiates the discharge in a discharge lamp. Starter is marked as S in the Figs.1 to 4. Starter less circuit are shown in Fig 5. They employ pre-heated filament electrodes. The preheating obtained through a small portion of voltage tapped from the input source.

When discharge lamps are used on dc the ballast takes the form of a resistor together with associated power loss. These days they take the form of an electronic ballast which converts dc to high frequency ac of around 20 kHZ.Except high pressure mercury lamp where V > VS (starting) all lamps need a starting device. At times, it is integral part of a lamp. Switch start employs bimetallic strip that opens upon

heating. Starterless, rapid start or instant starts are useful for outdoor applications. Other forms of starters employed are three electrode devices called ignitors.

Ignitors are small 3 electrode devices, which are ignited by control pulses from small electronic circuit. Typically Metal Halide lamps require 600 700V and Low Pressure Sodium Vapor lamps require 400- 600V. Ignition is through a Thyristor that generate a set of HV pulses, which

are stopped after Lamp glows or ignited. High Pressure Sodium Vapor Lamp needs about3000V.

Different Light Flux Levels are required at different times. This consists Local and General Lighting taken care by having dimmers and lamps of different wattages. Fig. 7 shows a typical Dimmer stat.

A dimmer stat is an autotransformer that can give a variable output voltage. Fig. 8 shows a typical metal halide lamp employing ignitor as a starting device.Fig. 9 shows a typical scheme for a multi watt circuit. Typically street lighting requires such multi watt lamps. High wattage lighting is employed during heavy traffic and low wattage during the rest of the night.This lecture thus covered the accessories necessary in an Illumination system.

An important issue in effective use of an illumination system is Glare. Glare by definition brightness within the field of vision that causes discomfort, annoyance interference and eye fatigue. It reduces the visibility of an object. This is the common fault of lighting installations. It injures the eye, disturbs the nervous system, causes discomfort and fatigue, reduces efficiency, interferes with clear vision and increases risk of accident.Glare is experienced, when Lamps, Windows, Luminaries, other areas are brighter than general brightness in the environment. Glare may be Direct and Reflected. Direct glare results from bright luminaire in the field of vision. Reflected glare arises due to reflection of such a source from a glossy surface it is more annoying than direct glare can be avoided by appropriate choice of interiors.Direct glare, minimization or avoidance is possible by mounting luminaries well above the line of vision or field of vision. Limit both brightness and light flux (in the normal field of view). Disability glare is that level of glare that impairs the vision. Whereas Discomfort glare only causes feeling of discomfort that increases or depends on time of exposure. There is no reduction of visual acuity but leads to fatigue. Annoyance is at lower ever luminance of the glare but source is more than the general luminance. Solid angle subtended at the observers eye in the field of view is a measure of glare. There is a need to look at the Glare Evaluation System.

Glare Evaluation

Visual comfort system is most common evaluation in the USA/Canada. This is expressed as percentage of people considering an installation comfortable as viewed from one end. Glare tables list various proportions and layout of room for glare free lighting. Figure of merit is based on a source of 1000 lm.from a luminaire. If VCP 70% then the system is said to be glare free. British method employs Zone of luminaire with a classification for quality of light expressed as Glare index. Luminance limit system is adopted in Australia. Standard code for Luminaire base lamp. dep. on room dimensions, mounting height and a Empirical shielding angle

Luminance curve system is employed in Europe.Luminance limits for luminaires critical angles, are 45 < < 85. Quality class is expressed from A to E type is based on Luminaire orientation.Type 1. Luminous sides when Luminous side plane> 30 mmType 2. Elongated - length > 2 width

Orientation C0 C180 Plane

Table I

Shielding AngleGlare LimitLamp

Luminance Cd/m2BDEFluorescent lamp.

L 2.1041000HP discharge lamp

2.104 < L 50.1041550LP Sodium lamp

L > 50.10430150HP Discharge clear

Table I lists for different types of lamps effective shielding angle. Quality class A denotes very high level; B denotes high, C medium D low and E very low.

General light is predominantly light coming downwards. Typically reflectance of 0.5 for walls /ceiling and 0.25 for furniture. How is Glare evaluated?1. Determine luminance of the source between 45 - 852. Determine the quality class and illuminance required.3. Select the curve class / level.4. Determine. Max. Angle to be considered from length & height and plane of eye level &plane of luminaires. (Refer to Fig 1)5. Horizontal limit based on a / h, part of the line ( or curve) to be ignored.6. Compare luminance of one luminaire with selected part of the limiting curve.

No glare if luminance given by the curve > actual luminance over the whole range of Emission.

Table II

Quality classService values of Illuminance (lux)Glare rating

Luminancecurve systemA200010005003001.15

B200010005003001.50

C200010005003001.85

E200010005003002.20

F200010005003002.55

Curveletterabcdefgh

British GlareIndex15,517,018,520,021,523,024,526,0

American VCP75%65%45%

Table II lists glare in dicer and curves to be used for different levels of illuminance and quality.

Quality classGService values of Illuminance (lux)

A1.1520001000500300

B1.5020001000500300

C1.8520001000500300

E2.2020001000500300

F2.5520001000500300

abcdefgh

Fig 4 and 5 show the luminaire curves to be employed for different levels for Type I luminaire and Type II luminaire.

hIllumA (B)IllumDIllumC

11.35 I/h21.4251.43 I/h2

21.72 I/h21.7981.827 I/h2

31.85 I/h21.9021.919 I/h2

41.91 I/h21.9431.95 I/h2

3

Illuminance at A (B) =

1 h1+

(i)

h 2

h 2 + 1

Namely height is an issue in avoiding glare. Fig. 6 shows two lamps placed at a height h from ground at A and B. As can be seen from relations (i), (ii),(iii). Illuminance below the lamp falls rapidly, less rapidly at the mid point C.

Illuminance at C = 1 h

3 *2

(ii)

h 2

h 2 + 0.25

3 3

1 h

h

Illuminance at D =

+

(iii)

h 2

h 2 + (0.75)2

h 2 + (0.25)2

h (i) (ii) (iii)

Glare from windows is the next issue. Sky has a typical luminance of 2000 Cd/m2. Horizontal Illuminance 10,000 lx. under overcast conditions. It is prevented by curtains, blinds, louvers. Opening of windows can be reduced. Shift the work plane away from offending windows. i.e. normal field of view no light enters from the offending window on the work plane. Lightest decorative finish on surfaces surrounding window openings. Veiling reflections and reflected glare are allowed outside the task. Reflected by glossy surface semi matt. Mild distraction can cause considerable discomfort. When glare (bright light) on the task. Veiling reflection reduce task contrast with some loss of details.Glare can be minimized by not locating in the forbidden zone, increase light from sideways at right angles to the direction of viewing.Luminaries having large surface area with low luminance may be employed. Working surface to be provided with reduced reflection preferably Matt surface

CRF (Contrast Rendition Factor) is yet another index and influence of Lighting on Task Contrast and Task Visibility is Contrast Rendition Factor. By definition

Task visibility =Given EmmisionSphere Illuminance

Where Sphere Illuminance is the Illuminance by the source providing equal Luminous Intensity in all directional in a hypothetical sphere. (ESI)

Observer is located / views at angle of 25 to the vertical. Observer considered to be viewing pencil task which id believed to be slightly conveying.

This lecture has had a look at glare, how originated various evaluation procedures and ways to minimize.

Interior Lighting

Interior Lighting is a complex problem depending on various factors such as

Purpose intended service,Class of Interiors.Luminaire best suited,Color effect andReflection from ceiling, walls, floors.

Good Lighting means intensity should be ample to see clearly and distinctly. The light distribution should be nearly uniform over a part of the room at least. It should be diffused that is soft and well diffused. Color depends on purpose and taste source but should approach daylight / yellow. Source location should be well above range of vision. To avoid glare intrinsic brightness is reduced by diffused glass ware and by remaining objects of secular reflection from range of vision. Shadows are a must for accentuating depth but should not too apparent abruptly or dense, they are not to be harsh and should toned down.

Standard practice is to have general lighting in all areas at a level comfortable to eye. It should eliminate dark shadows and avoid sharp contrast. In order to emphasize on parts that should be shown. Light sources located such that visual importance of object is kept in mind. Lamp may be concealed or counter lighted with a very low attention value to itself.Glare minimized by diffusing.

American Institute of Architects Recommends for Good Illumination.

1. General. Lighting effectively illuminate all objects/areas with due regard to relative importance in the interior composition. Adequate for eye comfort throughout the room elimination of dark shadows and sharp contrasts preserve soft shadows for roundness/relief lighting emphasis on those parts that need first attention.

2. Light sources be subordinated in visual importance to the things intended to illuminate, except rarely when itself is a dominant decorative element. Unless concealed/counter lighted, that they are not apparent they have extremely high attention value dominate the scheme.If visible so disposed to attract eye to major feature of room than themselves.

3. Glare must be eliminated. Result of intense brightness in concentrated areas within the line of vision. Produced by excess brightness of visible light.

reflection of bright lights from Polished low diffused surfaces - extreme contrast of light/shadeEmploy means of diffusing at source or finish the room - with Diffusing/Absorbing materials rather than reflecting material.

4. Level of illumination to be adequate for the type of eye work. Local lighting to supplement general lighting adequate illumination working at m/cs desks reading tables High level local lighting is always to be accompanied by general lighting to avoid eye strain and minimize controls. If glare is avoided there is no over illumination. Natural light limits are for outdoor 107600 lux and 1076 lux for indoor. Level should be adequate for eye task expected.

5. General lighting is to be related and controlled to suit the mood. While worship, meditation, introspection need low levels. Gaiety, mental activity, physical activity or intense activity needs high levels. Theaters, homes and restaurants may need levels varied according to mood. Shops level should be appropriate to woo customers through psychological reaction. Offices, factories and schools adequate illumination to work w/o eye strain.

6. Light source must suit interior in style, shape and finish in all architectural aspects.

Trends

It is always taken care to keep brightest surface not greater than 3 4 times brightness of task on hand whereas brightness of tasknot greater than 3 4 times darkest surface. That is to say luminance ratio from brightest to darkest is 10:3:1. Eliminating glare results in good visibility, eases viewing, and creates pleasing psychological effect. All the calls for large light sources covering entire ceiling approaching sheet of light. This ensures good uniform illumination all over the room! Commonly white ceiling with semi indirect luminaires. One may employ false ceiling (white or off white) with translucent diffusing material on top of which an array of lamps are located. Major defects in lighting design are too bright luminaires, too dark floors and furniture. Preferred scheme is to have light color interiors with large sources of low brightness. Day light illumination or natural illumination, constantly changes, varies with weather, time of the day or season. Typically lower daylight levels on upper levels. This required looking into openings or windows. It is observed that at 20 25' from window, daylight falls below 10lx under these conditions artificial general lighting needs to be turned on. Common technique is to partially screen them, thus makes uniform general lighting. Top section of window should be as close to ceiling as possible. It controls the light to the deepest end of the room. Normally height to top windownot less than the depth of the room. Window area is responsible for glare. Hence termed glare are. Glare area = 1/5th the floor space. Shades, baffles, louver, diffusers are employed to control glare

If X be the artificial illuminance that is sufficient for the task on hand: natural daylight illuminance (minimum) = 2X. Say windows are located only on one wall. Width of the room less than 2 times height to top of the window is preferred. Say windows are located on the opposite walls, width between the walls not greater than 6 times height to top of the window.

Location of lamps based on candle power, maximum allowable spacing, height at which located. Too great a spacing introduces dark shadows and dark spaces. Preferably lamps closer to ceiling, clear of obstructions are useful. They may be mounted on surface, suspended or recessed in the

ceiling. Typically tasks of great visual acuity are at a plane 1.2m above floor low hanging light units are used for local lighting. In using a matrix of lamps spacing not greater than mounting height.

Remembering that a plane source of light gives out light flux which produces illuminance independent of distance, mounting height is redundant when approaching a sheet of light.

Interior Finish

It is an important issue in interior lighting. Color reflectance affects utilization white or off white or yellow are preferred. Typical reflectance for Ceiling is 70 85%, for Walls is 45 60%, for Floor is 10 20%. In addition systems need to be maintained regular by Periodic check preferably when lux levels fall by 20 25%, time to replace lamps. Usually luminaires are likely to collect direct light. 1 times of minimum requirement is taken to take care of this. If voltage is maintained properly energy costs will be optimum. If voltage greater than labeled voltage, life is shortened. If voltage is less than labeled voltage, less light output results. Lamps and Luminaires are washed, cleaned. Direct lamps have less dirt, indirect lamps have more dirt. Luminaries are wiped with brush/dry cloth if necessary with a damp cloth. Grease removed by washing. Painting walls/ceiling every 1 - 2 years ensures good lighting levels. Clean offices may be lit using direct/indirect fluorescent lamps. Dusty smoky factory lit by mercury vapor direct or sodium vapor lamps. Replacement strategy should be related to large no. of lamps reach70% of life preferably in a group.

This lesson covered issues pertaining to interior lighting. Best thing is to approach near plane source of light. Reflectances of Walls, Ceiling and Floor also matter. Last but not least a good maintenance strategy is required.

Sports Lighting

This lesson addresses sports lighting application. Lighting for sports facility looks for comfort of four user groups namely Players, Officials, Spectators and Media. Players and officials should see clearly in the play area to produce best possible results the object used in the game. Spectators should follow the performance of the players. In addition to play area surroundings also need to be illuminated. Lighting should be such that it enables safe entry and exit. With increasing crowd level safety becomes more and more important. Media include TV and film, for whom lighting should provide lighting such that conditions are suitable for color picture quality as per CIE 83. This should be suitable for both general pictures as well as close up of players and spectators. Additionally, it should have provisions for emergency power supply to provide continuous transmission.

Criteria relevant for sports lighting are Horizontal Illuminance, Vertical Illuminance, IlluminanceUniformity, Glare restrictions, Modeling & shadows and Color appearance & rendering

Horizontal Illuminance

This becomes important as major part of view is illuminated playing area. Illuminance on the horizontal plane serves adaptation of the eye. It acts as a background, so adequate illuminance is important. For safe entry and exit adequate illumination is required in the circulation area also.

Vertical Illuminance

Sufficient contrast across players body is essential for the identification of the player. This is possible only if sufficient vertical illumination is there. This is characterized by both magnitude and direction. Players need adequate vertical illumination, from all directions. Spectators and Media need illumination only in defined directions. Generally, if horizontal illuminance is taken care, vertical illuminance levels become adequate. Usually vertical illuminance is specified or measured at a vertical height 1.5 m above the play area. Apart from player recognition and picture quality vertical illuminance should enable observation of movement of ball (or object moving in the sport concerned) above the playing field by both players and spectators. Spectators stands are also part of the environment and must also have adequate vertical illuminance, more from the safety point of view.

Illuminance Uniformity

Good illuminance is important in both the horizontal and vertical planes. If it be good it does away need for continuous adjustment of cameras. This is achieved by having Illuminance Uniformity. Uniformity of illumination is expressed by two indices:

(1).

U = Lowest Illuminance1Highest Illuminance

(2).U2 =

Lowest IlluminanceAverage Illuminance

For best conditions of Illumination ratio of average illuminance in the horizontal plane to vertical plane should be between 0.5 and 2.0.

Glare

When disturbing brightness nears or enters field of view, glare is said to be there. As already caused at low levels it could cause discomfort or annoyance but can be disabling at higher levels. It is minimized by a proper choice of flood lights or luminaries, located suitably and aimed in appropriate direction.

Modeling and Shadows

Ability of lighting to reveal form and texture provides overall pleasant impression of players, ball and spectators. It depends on direction of the light, no. and type of light sources. Shadows from narrow beams are termed hard are deep. The while light from luminous side lighting termed Flat produce no shadows. These are two extremes and are not desirable. Later improved by few spotlights. Good quality pictures on TV require good modeling. Hence, for media to limit shadows about 60 % light must come from main camera side and 40 % from opposite side.

Color Appearance and Color Rendering

Good color perception is very important for complete recognition. Some color distortion is acceptable in the field but becomes important for media transmission.

Color has two distinct aspects:

i.Color appearance of the light that takes care of color impression of the total environment, essentially due to the lamp.ii.Color rendering of the light, the ability to reproduce color of an object faithfully.

Depends on spectral energy distribution of light emitted. Color appearance obtained from color temperature varying between 2000 (warmer) to 6000 (cooler) K. Color rendering is specified by CRI or Ra. Maximum possible CRI being 100, which is comparable to day light situation. Higher the Ra more agreeable is the environment.

Table I lists the recommendations for various types of sports in terms of E Average MinimumHorizontal Illuminance and Illuminance Uniformity indices.

Table I

SportLevel of activityE (lux)U1U2RaTkGroup

AthleticsIndoor

Outdoort/r Ca Cp

t/r Ca Cp200300500

1002004000.30.40.5

0.20.20.30.50.50.7

0.30.30.5656565

202065200040004000

200020004000A

Badmintont/rCaCp3006008000.40.50.50.60.70.7656565400040004000B

BasketballIndoor

Outdoort/r Ca Cp

t/rCa300400600

1002000.40.50.5

0.20.30.60.70.7

0.30.4656565

6060400040004000

20002000B

CricketIndoor

Outdoort/r/CaCp

t/r/CaCp7501500

1002000.50.7

0.40.50.70.8

0.50.66565

656540004000

40004000C

FootballIndoor

Outdoort/r Ca Cp

t/r Ca Cp300600800

1002005000.40.50.5

0.40.50.50.60.70.7

0.60.70.7656565

656565400040004000

400040004000B

TableTennist/rCaCp3004006000.40.50.50.60.70.7606060400040004000C

TennisIndoor

Outdoort/r Ca Cp

t/r Ca Cp5007501000

2505007500.40.40.4

0.40.40.40.60.60.7

0.60.60.6656565

606565400040004000

200040004000B

Heret training amateur and professional r General recreationCa National competition amateurCp National and International competition, without media requirementsE Average minimum horizontal illuminanceU1 Illuminance uniformityEmin/Emax U2 Illuminance uniformityEmin/Eav Ra color rendering indexTk correlated color temperatureGroup according to CIE 83.

Initial values are taken to be 1.5 times indicated minimum levels. CIE grouping into A, B, C denotes speed of action in descending order. One may observe small ball size and high speed of movement are grouped under C. These recommendations change as shown in Table II for media coverage for National TV, while that for International coverage are as shown in Table III and for HDTV as shown in Table IV

Recommendations for TV (National)

Table II

GroupMaximum Shooting distanceIlluminance levelIlluminance verticalUniformityHorizontalColor Rend eringColor Temper ature

Maincamer a(lux)Secondarycamera(lux)U1U2U1U2

A 25m 75m 150m50070010005005007000.40.40.50.50.50.60.30.30.40.50.50.6656565400040004000

B 25m 75m 150m5001000140050070010000.50.50.60.60.60.70.30.30.40.50.50.6656565400040004000

C 25m 75m1000140070010000.50.60.60.70.40.40.60.6656540004000

Recommendations for TV (International)

Table III

GroupMaximum Shooting distanceIlluminance levelIlluminance verticalUniformityHorizontalColor Rende ringColor Temper ature

Maincamer a (lux)Secondary camera(lux)U1U2U1U2

A 25m 75m 150m7001000140050070010000.40.50.50.50.60.60.30.30.40.50.50.6656565400040004000

B 25m 75m 150m100014001750700100012500.50.60.60.60.70.70.30.40.40.50.60.6656565400040004000

C 25m 75m14001750100012500.60.70.70.80.40.50.60.7656540004000

Recommendations for HDTV

Table IV

GroupMaximum Shooting distanceIlluminance levelIlluminance verticalUniformityHorizontalColor Rende ringColor Temper ature

Maincamer a (lux)Secondary camera(lux)U1U2U1U2

A 25m 75m 150m100015002000700100015000.50.60.60.60.70.70.50.60.60.60.70.7909090550055005500

B 25m 75m 150m1500200025001000150017500.60.60.70.70.70.80.60.70.70.70.80.8909090550055005500

C 25m 75m20002500150017500.70.70.80.80.70.70.80.8909055005500

The recommended values are average Horizontal Illuminance values to be maintained throughout operation and installation.Therefore, initial values are taken 1.25 times these suggested values.

Vertical Illuminance is provided such that camera operators have free choice of camera angle. These levels are specified at a height of 1.5m above the playing area.

As seen from the recommendations, Illuminance uniformity is very stringent for TV or media although human eye is less sensitive and has ability to adjust, levels of uniformity required higher for TV coverage.

Metal Halide Lamps

Most sports installations employ metal halide lamps. They are similar to high pressure mercury lamps. It contains number of metal halides in addition to mercury. Halides are partly vaporized when normal operating temperature is reached. Hence dissociates into halogen and metal in the hot central region. Radiation attains the color of the metal employed.Groups of halides include:

1) three band color radiators2) multiline radiators3) molecular radiators

Three band radiator are Indium (In), Titanium (Ti), Sodium (Na). Multi Line radiator are Dyspersium (Dy), Hofnium(Ho), Thalum(Tm); Titanum (Ti), Sodium (Na) and Dyspersium (Dy), Titanium (Ti), Sodium (Na). Molecular radiators are Stannic Chloride (SnCl2) and Stannic Iodide ( SnI2) Essentially improve color rendering ability of a mercury vapor radiation.

Road Lighting

Road lighting provides visual conditions for safe, quick and comfortable movement of Road users.

The factors responsible for the lighting scheme for roads are:

i.Luminance Level.ii.Luminance Uniformity.iii.Degree of Glare limitation. iv.Lamp Spectra andv.Effectiveness of visual guidance.

Luminance Level

As the Luminance of a road influences contrast sensitivity of drivers eyes and contrast of obstacles, relative to back ground. Hence affects performance of Road users. Surrounding brightness affects the adaptation of human eye. Bright surroundings lower contrast sensitivity there by requiring higher luminance for the road surface. Darker surroundings make driver adapted to road (assuming road is brighter). Roads with dark surrounds are to be lit by including surroundings. Otherwise drivers cannot perceive objects in the surroundings. CIE 12 recommends that 5m away from the road on either side should be lit by illuminance level at least50% of that on the road.

Luminance Uniformity

Adequate uniformity is necessary for visual performance and visual comfort of the user. From visual performance view point, uniformity ratio is defined by U0 = Lmin / Lavg .U0 should not be below 0.4.From visual comfort view point uniformity ratio is defined as U1 = Lmin / Lmax measured along the line passing through the observer positioned in the middle of the traffic facing the traffic flow. Termed longitudinal uniformity ratio.

Glare Limitation

Physiological or disability glare affect visual performance. Psychological or discomfort glare affect visual comfort. Glare is to be avoided at all costs.

Lamp Spectra

Spectral composition determines color appearance of the lamp. The way lamp is going to render color to objects Low pressure sodium vapour lamps give greater visual acuity. Spectrum should be such; there is Great speed of perception, less discomfort glare and shorter recovery time after glare.

Visual Guidance

Visual guidance guides the road user and hence must for user to get a recognizable picture of the course immediately. This is improved by lamp arrangement that follows the run of the road. More so if turns and intersections are there. Lighting scheme must provide visual guidance. On roads having separate lanes with a separator the lighting columns are located on the separator. As is the custom in large avenues in Metros. On a curve the lighting column is located along the outer column. This gives a clear indication of the run of the road on the curvature. Visual guidance pilots traffic through lights of different colors on different routes. Exits on main roads are lit differently.Sodium vapour lamps for the main road and mercury lights for exits are employed.

Official Recommendations

National standards are taken from CIE 12. Visual conditions for smooth movement and safe traffic pattern. They depend on speed, intensity, composition of traffic and complexity of the road.

Table I lists the categories of the road as A to E based on the locality and traffic density. Table IIlists the appropriate recommendations for lighting.

Road categories

Table I

CategoryType and density of trafficType of RoadExamples

AHeavy and high speedmotorized traffic.Road with separators. Nocrossings. Complete access controlMotorwayExpressway

BImportant traffic road formotorized traffic only. Separate road for slow traffic/pedestrian.Trunk roadMajor road

CHeavy and moderatespeed motorized traffic or heavy mixed traffic of moderate speed.Important all purpose ruralor urban roadRing roadRadial road

DFairly heavy mixedtraffic of which a major part may be slow traffic or pedestrians.Roads in City or shoppingcenters, approach roads motorized traffic meets heavy slow or pedestrians.Trunk roadCommercial road Shopping streets etc.

EMixed traffic oflimited speed and moderateCollector road betweenresidential areasCollector roadLocal streets.

Recommendations for lighting

Table II

CategorySurroundsLuminance level. Average road surface luminance Lav(Cd/m2)Uniformity roadOverall Uniformity ratio ULengthwise Uniformity ratio UAAny20.4B12BrightDark210.40.7C12BrightDark210.40.40.5DBright20.40.5E12BrightDark10.50.40.40.50.501

Lighting Arrangements

Depending on the road category there are various arrangements for two way traffic roads. They are four types as shown in Fig. 1. They are:

a) Single sided located on one side, if width of the road mounting height. Luminance at the opposite remote end lower than under the lamp.

b) Staggered located on either side of the road in a staggered or zigzag fashion when width is 1 1.5 times the mounting height. Here care is to be taken to avoid dark patches.

c) Opposite located opposite one another. When width is greater than 1.5 times the mounting height.

d) Span wire luminnaires suspended along the axis of the road only normally for narrow roads. Suspended from cables strung between buildings.

aSingle sided

bStaggered

cOpposite

dSpan wire

Fig. 1 Lighting arrangement for 2 way street

High speed ways and dual lanes lamps may be located on the separator and are termed central twin bracket arrangement. As shown in Fig 2.

(a)(b)

Central TwinBracket

Central TwinBracket and opposite

Fig. 2 Lighting arrangement on the 2 Lane Roads.

Road Junctions

Special care is taken at road junctions as shown in Figs. 3 and 4. Care is taken such that junction is clearly visible from a distance. Should prevent traffic congestion. Higher luminance at junction. Using different colors at the junction. Different arrangements be for main roads and secondary roads. High mast lighting preferred at junctions.

Fig. 3 Crossing of major and minor roads roads.

Curves

Fig. 4 Crossing on a two lane highway.

Special care is taken on curves. On radius larger than 300m, the curve can be treated as straight roads. Smaller radius curves, lamps are located outside of the curve. Smaller the radius, closer is the spacing. Usually 0.5 0.25 times that for a straight road.

Tunnel lighting

Tunnels needs to be lit both during day and night. Sense of safety same as on open road. Tunnel for this purpose is divided into five zones Access zone, Threshold zone, Transition zone, Interior zone and Exit zone. Access zone is immediately outside the tunnel, where driver must be able to detect obstacles in the tunnel. Threshold zone is first of the four zones driver in the access zone must detect, obstacles in this zone before entering the tunnel. Length depends on the maximum speed and corresponding stopping distance. Transition zone is where levels can be gradually reduced. This is where reduction takes place. Interior zone is the Tunnel stretch farthest from influence of day light. Only artificial light enables drivers vision in this zone. Level is constant throughout depending on the speed, here highest level is chosen.Exit zone where vision is influenced by the brightness outside. Tunnels need extra day time lighting when tunnels are very long. CIE recommendation, including various aspects, needs at least for tunnel lengths.

Tunnel lengths < 25m no day time lighting, 25 125m 50% normal threshold zone lighting and >125m normal threshold zone lighting . Fig. 5 shows Tunnel lighting levels as a function of tunnel length.

EntranceL20

AccessZone

Lth

Transition

Lexit

Exit

Interior

Threshold Zone

Exit Zone

Fig. 5 Tunnel lighting levels

Tunnel lighting employs transverse and longitudinal light distributions which are symmetrical and counter beam system, which is asymmetrical. Transverse light radiated at 90 to the axis of the tunnel may be continuous line of tubular fluorescent lamps that give good visual guidance, minimal glare and require simple switching. Only disadvantage is close spacing. Longitudinal light radiated parallel to the tunnel axis. It leads to high efficacy and large luminaire spacing. Counter beam is light radiated parallel to the tunnel axis against the direction of traffic flow. In Residential area, road safety, security and amenity are kept in mind. Where only pedestrians are there, security and amenity are major criteria. In such areas high pressure mercury vapour lamps or blended lamps are preferred. Sodium vapor lamps of 50 / 70W have been successfully used. Wherever light needs to serve pedestrians post top lanterns are preferred.

Transverse

Longitudinal

Counter beam