16Lighting

16.1.1 Conversion Factors of Units of Illumination16.1.2 U.S. and Canadian Standards for Ballast Efficacy Factor16.1.3 Starting and Restrike Times among Different HID Lamps16.1.4 How Light Affects Color16.1.5 Summary of Light-Source Characteristics and Effects on Color16.2.1 Determination of Illuminance Categories16.3.1 Zonal Cavity Method of Calculating Illumination16.3.2 Coefficients of Utilization for Typical Luminaires16.3.3 Light-Loss Factor (LLF)16.3.4 Light-Loss Factors by Groups16.3.5 Light Output Change Due to Voltage Change16.3.6 Lumen Output for HID Lamps as a Function of Operating Position16.3.7 Lamp Lumen Depreciation16.3.8 Procedure for Determining Luminaire Maintenance Categories16.3.9 Evaluation of Operating Atmosphere16.3.10 Five Degrees of Dirt Conditions16.3.11 Luminaire Dirt Depreciation (LDD) Factors for Six Luminaire

Categories (I through VI) and for the Five Degrees of Dirtiness asDetermined from Figure 16.3.8 or Table 16.3.9

16.3.12 Room Surface Dirt Depreciation (RSDD) Factors16.3.13 Step-by-Step Calculations for the Number of Luminaires Required for a

Particular Room16.3.14 Reflectance Values of Various Materials and Colors16.3.15 Room Cavity Ratios16 3.16 Percent Effective Ceiling or Floor Cavity Reflectances for Various

Reflectance Combinations16.3.17 Multiplying Factors for Effective Floor Cavity Reflectances Other than

20 Percent (0.2)16.3.18 Characteristics of Typical Lamps16.3.19 Guide to Lamp Selection16.3.20 Recommended Reflectances of Interior Surfaces16.3.21 Recommended Luminance Ratios16.3.22 Average Illuminance Calculation Sheet

Section

16.1

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16.1.1 Conversion Factors of Units of Illumination

16.2 Section Sixteen

TABLE 16.1.1

16.1.2 U.S. and Canadian Standards for BallastEfficacy Factor

TABLE 16.1.2

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000,Courtesy of the Illuminating Engineering Society of North America.)

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Lighting 16.3

16.1.3 Starting and Restrike Times among DifferentHID Lamps

16.1.3

16.1.4 How Light Affects Color

Relationship of Light and Color. Light is the radiant energy produced by a lightsource. It may come to your eye directly from the source or be reflected or trans-mitted by some object.

Color is the interaction of the light source, the reflector or transmitter, and ourown ability to detect the color of light. Remember, you cannot perceive color with-out light. Different light sources radiate different wavelengths of light, influencingthe appearance of colored objects or surfaces.

Color Temperature. Color temperature describes how the lamp itself appearswhen lit. Color temperature is measured by Kelvin degrees, ranging from 9000 K(which appears blue) down to 1500 K (which appears orange-red). Light sourceslie somewhere between the two, with those of higher color temperature—4000 Kor more—being “cool” and those of lower color temperature—3100 K or less—being

(Reprinted from the IESNA Lighting Handbook, 9thEdition, 2000, Courtesy of the Illuminating EngineeringSociety of North America.)

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16.4 Section Sixteen

“warm.” Certain fluorescent lamps are intermediate types, lying somewherebetween cool and warm.

Color Rendition. Color rendition describes the effect a light source has on theappearance of colored objects. The color rendering capability of a lamp is measuredas the color rendering index (CRI). In general, the higher the CRI, the less distortionof the object’s color there is by the lamp’s light output. The scale used ranges from 0to 100. A CRI of 100 indicates that there is no color shift as compared with a refer-ence source, and the lower the CRI, the more pronounced the shift may be.

It is important to recognize that the reference source (and thus the CRI scale) isdifferent at different color temperatures. As a result, CRI values should only becompared between lamps of similar color temperatures.

Additional Factors Affect Color Appearance. The color rendering properties of a lampare an important influence on the color appearance of an object. However, manyother factors also affect color appearance, such as the finishes used on walls, floors,and furnishings; the intensity level of the lighting; and the presence of daylight in theroom. All these factors should be considered in selecting the appropriate light source.Additionally, the room decor is a critical consideration in selecting a light source. Ifcolors such as reds and oranges are the main element, a warm light source (color tem-perature below 3200 K) would be the best choice. Conversely, if blues and violets arebeing used, cool lamps (color temperature above 4000 K) should be used. Forareas with mixed cool and warm elements, or where neutral colors such as graypredominate, an intermediate color temperature source (3400 to 3600 K) shouldbe considered.

16.1.5 Summary of Light-Source Characteristicsand Effects on Color

TABLE 16.1.5

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Lighting 16.5

16.2.1 Determination of Illuminance Categories

TABLE 16.2.1

16.3.1 Zonal Cavity Method of CalculatingIllumination

The number of luminaires required to light a space to a desired illumination level(footcandles) can be calculated knowing certain characteristics of the room and lightsource. The following method is the zonal cavity method of calculating illumination.

�

where N � number of lampsCU � coefficient of utilization

LLF � light-loss factorE � recommended illumination (maintained)

N � lumens per lamp � CU � LLF�����

Footcandles required (E)Area

��Luminaire

(Reprinted from the IESNA Lighting Handbook, 9th Edition,2000, Courtesy of the Illuminating Engineering Society ofNorth America.)

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16.6 Section Sixteen

This formula can be rewritten to find the number of luminaires or to determine themaintained footcandle level:

Number of luminaires �

Footcandles �

The coefficient of utilization (CU) is a factor that reflects the fact that not all thelumens produced by a luminaire reach the work surface. It depends on the particularlight fixture used as well as the characteristics of the room in which it is placed,including the room size and the surface reflectances of the room. If you know thespecific luminaire you want to use, obtain CU factors from the manufacturer. Theyare usually included in product catalogs.

If you do not know specifically what fixture you will be selecting, you can use generalCU tables based on luminaire types (see Table 16.3.2).

16.3.2 Coefficients of Utilization forTypical Luminaires (pages 16.7–16.17)

16.3.3 Light-Loss Factor (LLF)

The light-loss factor (LLF) is a fraction that represents the amount of light thatwill be lost due to things such as dirt on lamps, reduction of light output of a lampover time, and similar factors. The following items are the individual componentsof the LLF. The total LLF is calculated by multiplying all the individual factorstogether. No factor should be ignored (set equal to 1) until investigations justifydoing so. Lighting calculations should not be attempted until all light-loss factorsare considered.

16.3.4 Light-Loss Factors by Groups (page 16.18)

Light-loss factors are divided into two groups: recoverable and nonrecoverable.Recoverable factors are those which can be changed by regular maintenance, suchas cleaning and relamping luminaires and cleaning or painting room surfaces.Nonrecoverable factors are those attributed to equipment and site conditions andcannot be changed with normal maintenance.

Nonrecoverable Factors

1. Luminaire ambient temperature factor. For normal indoor temperatures, use afactor of 1.

2. Heat-extraction thermal factor. For air-handling luminaires, use a factor of 1.10.

3. Voltage-to-luminaire factor. Assuming operation at rated nominal voltage, a factorof 1 can be used. For other conditions, refer to Figure 16.3.5.

4. Ballast factor. In general, refer to the manufacturer’s data. In the absence of that,the ballast factor depends on the lamp as well as on the ballast, so a ballast factordeveloped for a standard lamp does not apply when, for example, an energy-conserving lamp is used, even though the ballast is the same. Magnetic bal-lasts bearing the label of certified ballast manufacturers (CBM) have a ballastfactor that is not less than 0.925 for standard 30- and 40-W rapid-start lamps;the ballast factor for such ballasts is frequently estimated at between 0.94 and

N � lumens per lamp � CU � LLF�����

Area per luminaire

Footcandles required � area of room�����N � lumens per lamp � CU � LLF

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Lighting 16.7

TABLE 16.3.2

(continued)

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16.8 Section Sixteen

TABLE 16.3.2 (Continued)

(continued)

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Lighting 16.9

TABLE 16.3.2 (Continued)

(continued)

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16.10 Section Sixteen

TABLE 16.3.2 (Continued)

(continued)

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Lighting 16.11

TABLE 16.3.2 (Continued)

(continued)

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16.12 Section Sixteen

TABLE 16.3.2 (Continued)

(continued)

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Lighting 16.13

TABLE 16.3.2 (Continued)

(continued)

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16.14 Section Sixteen

TABLE 16.3.2 (Continued)

(continued)

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Lighting 16.15

TABLE 16.3.2 (Continued)

(continued)

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16.16 Section Sixteen

TABLE 16.3.2 (Continued)

(continued)

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Lighting 16.17

TABLE 16.3.2 (Continued)

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of NorthAmerica.)

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16.18 Section Sixteen

0.95. The ballast factor for highly loaded rapid-start lamps is 0.95 and for variouslow-wattage lamps is 0.90. A conservative estimate for a CBM-certified ballastwould be 0.93.

5. Ballast-lamp photometric factor. In general, refer to the manufacturer’s data oruse a factor of 1.

6. Equipment operating factor. For HID lamp-ballast-luminaire combination only,refer to the manufacturer’s data or use a factor of 1.

7. Lamp-position (tilt) factor. Part of the equipment operating factor. Refer to Figure16.3.6 for typical average data and to manufacturers for specific lamp types.

8. Luminaire surface depreciation factor. Over time, the various surfaces of a lightfixture will change (some plastic lenses yellow, for example). In the absence ofdata, use a value of 1.

Recoverable Factors

1. Lamp lumen depreciation factor. All lamps put out less light as they age.Specific information is available from each manufacturer, or you can use thefigures in Table 16.3.7 for preliminary calculations.

2. Luminaire dirt depreciation (LDD) factor. The accumulation of dirt on lumi-naires results in a loss of light output and therefore a loss of light on the work-plane. This loss is known as the luminaire dirt depreciation LDD factor and isdetermined as follows:a. The luminaire maintenance category is selected from the manufacturer’s data

or by using Table 16.3.8.b. The atmosphere (one of five degrees of dirt conditions) in which the lumi-

naire operates is found as follows. Dirt in the atmosphere comes from twosources—that passed from adjacent air and that generated by work done inthe vicinity. Dirt may be classified as adhesive, attracted, or inert, and it maycome from intermittent or constant sources. Adhesive dirt clings to luminairesurfaces by its stickiness, whereas attracted dirt is held by electrostatic force.Inert dirt varies in accumulation from practically nothing on vertical surfacesto as much as a horizontal surface holds before the dirt is dislodged by gravityor air circulation. Examples of adhesive dirt are grease from cooking, particles

TABLE 16.3.4 Light-Loss Factors by Groups

(Reprinted from the IESNA LightingHandbook, 9th Edition, 2000, Courtesyof the Illuminating Engineering Societyof North America.)

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Lighting 16.19

from machine operation borne by oil vapor, particles borne by water vapor asin a laundry, and fumes from metal-pouring operations or plating tanks.Examples of attracted dirt are hair, lint, fibers, and dry particles that areelectrostatically charged from machine operations. Examples of inert dirtare nonsticky, uncharged particles such as dry flour, sawdust, and fine cin-ders. Tables 16.3.9 and 16.3.10 may be useful for evaluating the atmosphere.Table 16.3.10 is intended to evaluate the atmosphere-dirt category. Factors1 to 5 should be assessed and inserted into the spaces in Table 16.3.9because they are required to describe the conditions of the space. The “AreaAdjacent to Task Area” column represents the area separated from but adja-cent to the area in which the luminaire operates (which is the “AreaSurrounding Task”). The “Filter Factor” column contains the percentages ofdirt allowed to pass from the adjacent atmosphere to the surrounding atmos-phere. The “From Adjacent” column indicates the net amount of such dirtthat can pass through. This category might include, for example, an openwindow with a filter factor of 1.0 (no filtering at all) or an air-conditioningsystem with a filter factor of 0.1 (90 percent of the dirt is filtered out). Thetotal of all the numbers in the “Subtotal” column is a number up to 60 andcan be translated into the applicable atmosphere-dirt category listed at thebottom of the table.

c. From the appropriate luminaire maintenance category curve of Figure16.3.11, the applicable dirt condition curve, and the proper elapsed time inmonths of the planned cleaning cycle, the LDD factor is found. For example,if the category is I, the atmosphere is dirty, and the cleaning occurs every 20months, the LDD is approximately 0.80.

3. Room surface dirt depreciation (RSDD) factor. The accumulation of dirt onroom surfaces reduces the amount of luminous flux reflected and interreflectedto the workplane. To take this into account, Figure 16.3.12 has been developedto provide RSDD factors for use in calculating maintained average illuminancelevels. These factors are determined as follows:a. From one of the five curves in Figure 16.3.12, find the expected dirt depreci-

ation using Table 16.3.9 or 16.3.10 as a guide to atmospheric dirt conditions,together with an estimate of the time between cleanings. For example, if theatmosphere is dirty and room surfaces are cleaned every 24 months, theexpected dirt depreciation is 30 percent.

b. Knowing the expected dirt depreciation (step a), the type of luminaire distri-bution, and the room cavity ratio (RCR), determine the RSDD factor fromFigure 16.3.12. For example, for a dirt depreciation of 30 percent, a directluminaire, and a room cavity ratio of 4, the RSDD would be 0.92.

4. Lamp burnout (LBO) factor. If lamps are replaced as they burn out, use a factor of0.95. If a group replacement maintenance program is employed, use a factor of 1.

16.3.5 Light Output Change Due to Voltage Change(see page 16.20)

16.3.6 Lumen Output for HID Lamps as a Functionof Operating Position (see page 16.20)

16.3.7 Lamp Lumen Depreciation (see page 16.20)

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16.20 Section Sixteen

16.3.6

0 10 20 30 40 50 60 70 80 90Operating angle from vertical in degrees

Per

cent

of v

ertic

al lu

men

s 100

90

80

70

TABLE 16.3.7

16.3.5

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000,Courtesy of the Illuminating Engineering Society of NorthAmerica.)

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000,Courtesy of the Illuminating Engineering Society of NorthAmerica.)

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Lighting 16.21

16.3.8

16.3.8 Procedure for Determining LuminaireMaintenance Categories

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the IlluminatingEngineering Society of North America.)

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16.22 Section Sixteen

16.3.11 Luminaire Dirt Depreciation (LDD) Factorsfor Six Luminaire Categories (I through VI) and forthe Five Degrees of Dirtiness as Determined fromFigure 16.3.8 or Table 16.3.9 (see page 16.23)

16.3.12 Room Surface Dirt Depreciation (RSDD)Factors (see page 16.23)

TABLE 16.3.10

16.3.9 Evaluation of Operating Atmosphere

16.3.10 Five Degrees of Dirt Conditions

TABLE 16.3.9

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of NorthAmerica.)

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of NorthAmerica.)

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Lighting 16.23

TABLE 16.3.12

16.3.11

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of NorthAmerica.)

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of NorthAmerica.)

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16.24 Section Sixteen

16.3.13 Step-by-Step Calculations for the Numberof Luminaires Required for a Particular Room

1. Compile the Following Information:

� Length and width of room.� Height of floor cavity; the distance from the floor to the work surface (usually

taken as 2.5 ft).� Height of the ceiling cavity; the distance from the ceiling to the light fixture. If

the fixture is recessed or ceiling- (surface-) mounted, the value is zero.� Height of the room cavity; the distance from the work surface to the light fixture.� Surface reflectances of the ceiling, the walls, and the floor. If the wall surface of

the floor cavity is different from the room cavity wall surface (as with a wainscot,for example) obtain both figures. Surface reflectances are usually available frompaint companies, ceiling tile manufacturers, and manufacturers of other finishes.If these are not readily available, use the values in Table 16.3.14.

2. Determine Cavity Ratios.

CR � 2.5 �

For rectangular spaces, the formula becomes

CR � 5h �

where h � height of the cavityl � length of the room

w � width of the room

Note that if the work surface is the floor, or if the luminaires are surface-mounted,the floor cavity ratio and ceiling cavity ratio, respectively, are zero. Also, since thethree cavity ratios are related, after finding one, you can find the other two ratios by:

CCR � RCR � �

FCR � RCR � �where CCR � ceiling cavity ratio

FCR � floor cavity ratioRCR � room cavity ratio

hcc � height of ceiling cavityhfc � height of floor cavityhrc � height of room cavity

You can find the cavity ratios by calculation or use the values given in Table16.3.15. First, find the RCR, and then use the ratios to find the values of the CCRand FCR.

hfc�hrc

hcc�hrc

l � w�l � w

Area of cavity wall���Area of base of cavity

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Lighting 16.25

3. Determine the Effective Ceiling Cavity Reflectance and the Effective Floor CavityReflectance. These are values of the imaginary planes at the height of the luminaireand the work surface that will be used in finding the coefficient of utilization of aparticular light fixture. If the luminaires are recessed or surface-mounted, theeffective ceiling cavity reflectance is the same as the reflectance of the ceiling itself.Use Table 16.3.16 to find the effective reflectances, knowing the cavity ratios youdetermined in step 2.

4. Determine the Coefficient of Utilization of the Fixture under Consideration by Using theCU Tables from the Manufacturer’s Literature or Table 16.3.2. Straight-line interpolationprobably will be necessary. Most tables are set up for a floor reflectance of 20 percent.If the effective floor reflectance varies significantly from this, use the correctionfactors given in Table 16.3.17 and multiply by the CU for the fixture.

5. Determine the Recommended Illumination for the Space Being Designed. Refer toTable 16.2.1.

6. Determine the Lumen Output of the Lamps That Will Be Used in the Luminaire YouHave Selected. Values for lumen output for some representative lamps are givenin Table 16.3.18. More accurate data can be obtained from the fixture manufactur-er or a lamp manufacturer. Determine the number of lamps that will be used ineach luminaire.

7. With the Information Compiled in the Previous Steps and with the Light-Loss Factor(LLF), Use the Following Formula:

Number of luminaires �

You also can determine the area per luminaire using the formula given at thebeginning of this section.

Footcandles required � area of room�����N � lumens per lamp � CU � LLF

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16.26 Section Sixteen

16.3.15 Room Cavity Ratios (see page 16.27)

TABLE 16.3.14

16.3.14 Reflectance Values of VariousMaterials and Colors

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Lighting 16.27

TABLE 16.3.15

16.3.16 Percent Effective Ceiling or Floor CavityReflectances for Various Reflectance Combinations(see pages 16.28 –16.29)

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TABLE 16.3.16 Percent Effective Ceiling or Floor Cavity Reflectances for Various Reflectance Combinations*

(continued)

16.28

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TABLE 16.3.16

16.29

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)

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16.30 Section Sixteen

16.3.17 Multiplying Factors for Effective FloorCavity Reflectances Other than 20 percent (0.2)

TABLE 16.3.17

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of NorthAmerica.)

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Lighting 16.31

16.3.18 Characteristics of Typical Lamps

TABLE 16.3.18

(continued)

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16.32 Section Sixteen

16.3.19 Guide to Lamp Selection(see pages 16.33–16.34)

TABLE 16.3.18 (Continued)

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TABLE 16.3.19

(continued)

16.33

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TABLE 16.3.19 (Continued)

16.34

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Lighting 16.35

16.3.20 Recommended Reflectances of InteriorSurfaces

TABLE 16.3.20

TABLE 16.3.21

16.3.21 Recommended Luminance Ratios

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16.36 Section Sixteen

16.3.22 Average Illuminance Calculation Sheet

16.3.22

(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of NorthAmerica.)

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