Lighting fundamentals - eap.grip2013.eap.gr/pdf/GR_Topalis_Lighting_fundamentals.pdf · Lighting...
Transcript of Lighting fundamentals - eap.grip2013.eap.gr/pdf/GR_Topalis_Lighting_fundamentals.pdf · Lighting...
About light and photometrics
• Generation of light
• Human vision
• Black body
• Colour
• Basic principles of lighting
• Light sources
What is light?
• Light is electromagnetic radiation
and
• The human eye is sensible to this radiation
Light generation
E2 = energy associated with the excited orbit
E1 = energy associated with the normal orbit
h = Planck's constant
f = frequency of the emitted radiation as the electron moves from level 2 to level 1
h
EffhEEE
12
f
vn
λ=wavelength of radiation
n=index of refraction of the medium
How light excites the eye?
Through sensors in the retina
Two types of sensors:
• Cones (6-7 millions per eye)
• Rods (around 120 millions per eye)
Location of cones and rods
• Cones: Mainly around the central area of the retina (fovea)
• Rods: Towards the periphery of the retina (max at ±20o)
Cones
• Axial vision (±5o=10o visual field)
• Less sensitive than rods
• Their sensitivity decreases at low light levels
• Photopic vision (daylight, illuminated areas)
• Responsible for colour recognition
• Highest sensitivity at 555 nm
Rods
• Peripheral vision & motion detection
• 1000 times more sensitive than cones
• They function under low light levels (dark adapted)
• Scotopic vision (night vision)
• No colour recognition (at night we see in shades of grey!)
• Highest sensitivity at 507 nm
Colour of light sources
• How do we measure the colour of light sources?
– Comparing the colour of the light of the source with the colour of the radiation of a “black body” (Planckian radiator, black body of Max Planck)
The black body
– Theoretical
– Definitely not only black in colour
– A black painted body absorbs only the visible light (but not UV, IR, X-rays etc)
– The black body (Planckian radiator) absorbs ALL radiations
How the black body works?
• It is characterized by 2 physical quantities: Temperature and wavelength of radiation
• It absorbs an external radiation (any radiation). This increases its temperature – External radiation Absorption Temperature rise
• It radiates. The wavelength of its radiation depends on its temperature
– Black body radiation ~ Black body temperature
Black body radiation, Law of Max Planck, Nobel award 1918
Pλ Watts of black body radiation/m2 of black body surface/m of wavelength
h Planck’s constant (6,626·10-34 J·s)
c Speed of light (2,99792·108 m/s)
k Boltzman’s constant (1,38·10-23 J/K)
λ Wavelength (m)
t Temperature of black body (Κ)
Wien’s law of displacement
λmax·Temperature=Constant
If the temperature of the black body rises, then the peak of the
spectrum moves towards the lower
wavelengths
Colour temperature
• Colour temperature is a measure for describing the colour of light sources
• It indicates the equivalent temperature that a black body would need to have in order to produce light of the same colour
• Thus, we express the colour of a light source with the temperature (in Kelvins) of the respective black body
Colour temperature vs. black body temperature
Low colour temperature (“cold” black body)
indicates warm light colour Confusion!
Definition of colour quality
The colour quality of a light source is
expressed by a value between 0 and 100
known as Colour Rendering Index (CRI) or Ra
Test strips are illuminated from the light
source and the reflected light is measured.
CRI is the effective sum of the reflected light.
What is light?
• Light is a radiation that is detected by the eye
• Therefore, the generation of light depends on: – the power P(λ) of the radiation
and
– the spectral sensitivity V(λ) of the eye
nm
nm
dVP
780
380
)()(
Luminous flux
The measure of the quantity of light is called luminous flux and is defined as:
nm
nm
m dVPK
780
380
)()(
Φ is measured in lumen (abbreviation: lm)
P(λ) in Watt
Km=683lumen/Watt
How do we measure light?
• The light source is treated as a point
• Let’s imagine that point source emitting light to all directions
• The light to each direction is emitted from the point source in a virtual cone
• This cone is called “solid angle”
Solid angle
• The light from the –point- source is emitted in solid angles
• Solid angle is the 3-dimensional equivalent of a 2-dimensional angle
Definition of solid angle Given a sphere of radius r, a cone that subtends
an area A encloses a solid angle Ω
Unit: Steradian
Abbreviation: sr
Plane and solid andles Plane angle
Solid angle
The solid angle Ω is produced
by rotating the plane angle γ
Luminous intensity
Luminous intensity I is the amount of
luminous flux dΦ (lumens) per unit
solid angles dΩ (steradians)
d
dI
Definition of luminous intensity
• Luminous intensity describes the power of the light source to emit light in a given direction
• It is the fraction of the luminous flux of the source that is emitted into a certain direction, into a certain solid angle
d
dI
steradian
lumencandela
1
11
Definition of illuminance
Illuminance is the luminous flux density on the illuminated surface
Unit: lux (lx)
dA
dE
21
11
m
lumenlux
The acuity of vision is not increased after a certain illuminance level
For common duties our visual perception is not improved at more than 3000 lux
Illuminance meters(Luxmeters)
Portable
• General use
• More accurate with mili Lux resolution
Benchtop for laboratories
Pseudo-colour Isolux diagram of road illumination
18
16
14
12
10
8
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
Y(m)
10
86
42
0-2
-4
X(m
)
AAAAAAA
AAAAAAA
Luminance
Luminance L is defined as the luminous intensity I in a specific direction of a light source or of a surface that reflects light, divided by the projected area A as viewed from that direction
Unit: candela/m2 (cd/m2)
A
IL
Illuminance is proportional to the cosine of the angle of incidence
cos12 EE
The same flux is spread over a larger area
The beam angle
Beam angle: The angle at which the lighting intensity takes 50% of the maximum intensity
A typcial UGR table of a luminaire
H: Height of luminaire from working plane S: Spacing between luminaires
ρ: Reflectance of ceiling, walls, floor
X, Y: Length and Width of room
Reduction of glare
A luminaire with high UGR i.e. with high glare
A luminaire with low UGR i.e. with low glare
Light Output Ratio (LOR)
LOR=0.67 means that the emitted flux is 67% of the produced
lampsthebyproducedfluxousLu
aireluthebyemittedfluxousLuLOR
min
minmin
Utilization factor (UF or CU)
• The percentage of the luminous flux of the lamps that falls on the working plane i.e the “useful” luminous flux
lampsthebyproducedfluxousLu
planeworkingtheonfluxousLuUF
min
min
• In Europe: Utilization Factor (UF)
• In USA: Coefficient of Utilization (CU)
• Example
– UF=0.68
– The luminous flux falling on the working plane is 68% of the total luminous flux of the luminaire lamps
Utilization Factor depends on:
• the room dimensions
• the reflectance of the room surfaces
• the height of luminaires from the working plane
• the spacing between luminaires
The influence of the dimensions of the room is integrated in one size: the room index Κ
( )m
L WK
h L W
Working plane
Συντελεστής χρησιμοποίησης (παράδειγμα)
Utilization factors
Nominal spacing-to-height ratio (SHRNOM) = 1
Reflectance
Suspension ratio J=0 Suspension ratio J=1/4
ρ-ceiling 0.80 0.80 0.80 0.70 0.70 0.70 0.50 0.50 0.50 0.80 0.80 0.80 0.70 0.70 0.70 0.50 0.50 0.50
ρ-walls 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30
ρ-working
plane 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20
Room
index
K
0.60 0.31 0.24 0.20 0.30 0.24 0.20 0.29 0.23 0.20 0.30 0.23 0.20 0.29 0.23 0.20 0.28 0.23 0.20
0.80 0.36 0.29 0.25 0.35 0.29 0.25 0.33 0.28 0.24 0.34 0.28 0.24 0.34 0.28 0.24 0.33 0.28 0.24
1.00 0.40 0.34 0.29 0.39 0.33 0.29 0.37 0.32 0.28 0.38 0.32 0.29 0.38 0.32 0.28 0.36 0.31 0.28
1.25 0.43 0.38 0.33 0.42 0.37 0.33 0.40 0.36 0.32 0.42 0.36 0.33 0.41 0.36 0.32 0.40 0.35 0.32
1.50 0.46 0.40 0.37 0.44 0.40 0.36 0.42 0.38 0.35 0.45 0.39 0.36 0.44 0.39 0.35 0.42 0.38 0.35
2.00 0.49 0.45 0.41 0.48 0.44 0.41 0.46 0.42 0.40 0.48 0.44 0.41 0.47 0.43 0.40 0.45 0.42 0.39
2.50 0.51 0.47 0.44 0.50 0.46 0.44 0.47 0.45 0.42 0.50 0.46 0.43 0.49 0.46 0.43 0.47 0.44 0.42
3.00 0.53 0.49 0.46 0.51 0.48 0.46 0.49 0.46 0.44 0.52 0.48 0.46 0.51 0.48 0.45 0.49 0.46 0.44
4.00 0.54 0.52 0.49 0.53 0.51 0.49 0.51 0.49 0.47 0.54 0.51 0.49 0.53 0.50 0.48 0.50 0.48 0.46
5.00 0.55 0.53 0.51 0.54 0.52 0.50 0.52 0.50 0.49 0.55 0.53 0.51 0.54 0.52 0.50 0.51 0.50 0.48
Indoor luminaire
• Length: 15 m
• Width: 5 m
• Height: 3 m
• Thus: ( )
15 5
3 (15 5)
1.25
m
L WK
h L W
K
K
The Maintenance Factor (MF)
113
• The lighting installation is depreciated over the time
(ageing of lamps, depreciation of optical materials, dirt
over the reflecting surfaces etc)
• The lighting designer estimates that depreciation
quantitevely (MF) and increases respectively the initial
lighting level
• Over the time, that lighting level will be decreased due
to the ageing and the dirt.
• Thus, the initially high lighting level will be decreased,
over the time, to a level not lower than the required.
An example
114
• Required illuminance revel: 500 lux
• Estimated depreciation: 20%
• Maintenance factor (MF): 0.80 (80%)
• Initial illuminance level: 500/0.80=625 lux
• The initial 625 lux will be gradually decreased due to
the ageing and the accumulation of dirt to:
625X0.80=500 lux i.e. at the required level
MF sums the depreciation of the
lighting system due to the factors:
• Lamp lumen maintenance factor (LLMF)
• Lamp survival factor (LSF)
• Luminaire maintenance factor (LMF)
• Room surface maintenance factor (RSMF)
MF = LLMF Χ LSF Χ LMF Χ RSMF
The depreciation factors depend on the
maintenance interval
Luminaire maintenance factor (LMF)
Lamp lumen maintenance factor
(LLMF)
Lamp survival factor (LSF)
A fast method to determine MF
Description of the room & equipment Maintenance factor
Very clean room, cleaning of luminaires once per year, burning of lamps 2000
hours/year, type of luminaires of direct lighting with protection from the
accumulation of dust
0.80
Typically clean room, cleaning of luminaires once per 3 years, burning of lamps
2000 hours/year, type of luminaires of direct/indirect lighting without protection
from the accumulation of dust
0.70
Room with pollution, cleaning of luminaires once per 3 years, burning of lamps
8000 hours/year, grouped replacement of lamps every 8000 hours, luminaires
without protection from the accumulation of dust
0.50
CIE Flux Code
Examples: CIE 30 40 50 100 65, CIE 48 78 95 99 70
2
2/1001
N
2
1002
N
2
2/31003
N
lum
N
2100
4
21004
lamp
lumN
100
5
LORN 5
An example of the CIE Flux Code of a luminaire
CIE 48 78 95 99 70
Φπ/2=0,48· Φ2π: 48% of the downward flux is emitted in the solid angle Ω=π/2
Φπ=0,78·Φ2π: 78% of the downward flux is emitted in the solid angle Ω=π
Φ3π/2=0,95·Φ2π: 95% of the downward flux is emitted in the solid angle Ω=2π/3
Φ2π=0,99Φlum: 99% of the total flux of the luminaire is emitted downwards.
Thus only 1% of the total flux of the luminaire is emitted upwards.
Φlum=0,70·Φlamp: The luminaire emits in the room 70% of the total flux of the
lamps. Thus LOR = 70%