Light Loss Factor Criteria 2b5l6e
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Page 16.6
Section Sixteen
This formula can be rewritten to find the number of luminaires or to determine the maintained footcandle level: Footcandles required area of room Number of luminaires N lumens per lamp CU LLF N lumens per lamp CU LLF Footcandles Area per luminaire The coefficient of utilization (CU) is a factor that reflects the fact that not all the lumens produced by a luminaire reach the work surface. It depends on the particular light 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 the specific luminaire you want to use, obtain CU factors from the manufacturer. They are usually included in product catalogs. If you do not know specifically what fixture you will be selecting, you can use general CU tables based on luminaire types (see Table 16.3.2).
16.3.2 Coefficients of Utilization for Typical 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 that will be lost due to things such as dirt on lamps, reduction of light output of a lamp over time, and similar factors. The following items are the individual components of the LLF. The total LLF is calculated by multiplying all the individual factors together. No factor should be ignored (set equal to 1) until investigations justify doing so. Lighting calculations should not be attempted until all light-loss factors are 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, such as cleaning and relamping luminaires and cleaning or painting room surfaces. Nonrecoverable factors are those attributed to equipment and site conditions and cannot be changed with normal maintenance. Nonrecoverable Factors
1. Luminaire ambient temperature factor. For normal indoor temperatures, use a factor 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 factor of 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 factor developed for a standard lamp does not apply when, for example, an energyconserving lamp is used, even though the ballast is the same. Magnetic ballasts bearing the label of certified ballast manufacturers (CBM) have a ballast factor 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
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16.7
TABLE 16.3.2
(continued)
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Section Sixteen
TABLE 16.3.4 Light-Loss Factors by Groups
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
0.95. The ballast factor for highly loaded rapid-start lamps is 0.95 and for various low-wattage lamps is 0.90. A conservative estimate for a CBM-certified ballast would be 0.93. 5. Ballast-lamp photometric factor. In general, refer to the manufacturer’s data or use 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 Figure 16.3.6 for typical average data and to manufacturers for specific lamp types. 8. Luminaire surface depreciation factor. Over time, the various surfaces of a light fixture will change (some plastic lenses yellow, for example). In the absence of data, 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 the figures in Table 16.3.7 for preliminary calculations. 2. Luminaire dirt depreciation (LDD) factor. The accumulation of dirt on luminaires results in a loss of light output and therefore a loss of light on the workplane. This loss is known as the luminaire dirt depreciation LDD factor and is determined 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 luminaire operates is found as follows. Dirt in the atmosphere comes from two sources—that ed from adjacent air and that generated by work done in the vicinity. Dirt may be classified as adhesive, attracted, or inert, and it may come from intermittent or constant sources. Adhesive dirt clings to luminaire surfaces by its stickiness, whereas attracted dirt is held by electrostatic force. Inert dirt varies in accumulation from practically nothing on vertical surfaces to as much as a horizontal surface holds before the dirt is dislodged by gravity or air circulation. Examples of adhesive dirt are grease from cooking, particles
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from machine operation borne by oil vapor, particles borne by water vapor as in a laundry, and fumes from metal-pouring operations or plating tanks. Examples of attracted dirt are hair, lint, fibers, and dry particles that are electrostatically charged from machine operations. Examples of inert dirt are nonsticky, uncharged particles such as dry flour, sawdust, and fine cinders. 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. Factors 1 to 5 should be assessed and inserted into the spaces in Table 16.3.9 because they are required to describe the conditions of the space. The “Area Adjacent to Task Area” column represents the area separated from but adjacent to the area in which the luminaire operates (which is the “Area Surrounding Task”). The “Filter Factor” column contains the percentages of dirt allowed to from the adjacent atmosphere to the surrounding atmosphere. The “From Adjacent” column indicates the net amount of such dirt that can through. This category might include, for example, an open window with a filter factor of 1.0 (no filtering at all) or an air-conditioning system with a filter factor of 0.1 (90 percent of the dirt is filtered out). The total of all the numbers in the “Subtotal” column is a number up to 60 and can be translated into the applicable atmosphere-dirt category listed at the bottom of the table. c. From the appropriate luminaire maintenance category curve of Figure 16.3.11, the applicable dirt condition curve, and the proper elapsed time in months 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 20 months, the LDD is approximately 0.80. 3. Room surface dirt depreciation (RSDD) factor. The accumulation of dirt on room surfaces reduces the amount of luminous flux reflected and interreflected to the workplane. To take this into , Figure 16.3.12 has been developed to provide RSDD factors for use in calculating maintained average illuminance levels. These factors are determined as follows: a. From one of the five curves in Figure 16.3.12, find the expected dirt depreciation 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 the atmosphere is dirty and room surfaces are cleaned every 24 months, the expected dirt depreciation is 30 percent. b. Knowing the expected dirt depreciation (step a), the type of luminaire distribution, and the room cavity ratio (RCR), determine the RSDD factor from Figure 16.3.12. For example, for a dirt depreciation of 30 percent, a direct luminaire, 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 of 0.95. 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 Function of Operating Position (see page 16.20) 16.3.7
Lamp Lumen Depreciation (see page 16.20)
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Section Sixteen
16.3.5
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
Percent of vertical lumens
16.3.6 100 90 80 70
0
10
20
30
40
50
60
70
80
90
Operating angle from vertical in degrees (Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
TABLE 16.3.7
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16.3.8 Procedure for Determining Luminaire Maintenance Categories 16.3.8
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
16.21
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Section Sixteen
16.3.9 Evaluation of Operating Atmosphere TABLE 16.3.9
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
16.3.10 Five Degrees of Dirt Conditions TABLE 16.3.10
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
16.3.11 Luminaire Dirt Depreciation (LDD) Factors for Six Luminaire Categories (I through VI) and for the Five Degrees of Dirtiness as Determined from Figure 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)
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16.23
16.3.11
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
TABLE 16.3.12
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
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Page 16.6
Section Sixteen
This formula can be rewritten to find the number of luminaires or to determine the maintained footcandle level: Footcandles required area of room Number of luminaires N lumens per lamp CU LLF N lumens per lamp CU LLF Footcandles Area per luminaire The coefficient of utilization (CU) is a factor that reflects the fact that not all the lumens produced by a luminaire reach the work surface. It depends on the particular light 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 the specific luminaire you want to use, obtain CU factors from the manufacturer. They are usually included in product catalogs. If you do not know specifically what fixture you will be selecting, you can use general CU tables based on luminaire types (see Table 16.3.2).
16.3.2 Coefficients of Utilization for Typical 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 that will be lost due to things such as dirt on lamps, reduction of light output of a lamp over time, and similar factors. The following items are the individual components of the LLF. The total LLF is calculated by multiplying all the individual factors together. No factor should be ignored (set equal to 1) until investigations justify doing so. Lighting calculations should not be attempted until all light-loss factors are 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, such as cleaning and relamping luminaires and cleaning or painting room surfaces. Nonrecoverable factors are those attributed to equipment and site conditions and cannot be changed with normal maintenance. Nonrecoverable Factors
1. Luminaire ambient temperature factor. For normal indoor temperatures, use a factor 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 factor of 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 factor developed for a standard lamp does not apply when, for example, an energyconserving lamp is used, even though the ballast is the same. Magnetic ballasts bearing the label of certified ballast manufacturers (CBM) have a ballast factor 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
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Page 16.7
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16.7
TABLE 16.3.2
(continued)
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Page 16.18
Section Sixteen
TABLE 16.3.4 Light-Loss Factors by Groups
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
0.95. The ballast factor for highly loaded rapid-start lamps is 0.95 and for various low-wattage lamps is 0.90. A conservative estimate for a CBM-certified ballast would be 0.93. 5. Ballast-lamp photometric factor. In general, refer to the manufacturer’s data or use 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 Figure 16.3.6 for typical average data and to manufacturers for specific lamp types. 8. Luminaire surface depreciation factor. Over time, the various surfaces of a light fixture will change (some plastic lenses yellow, for example). In the absence of data, 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 the figures in Table 16.3.7 for preliminary calculations. 2. Luminaire dirt depreciation (LDD) factor. The accumulation of dirt on luminaires results in a loss of light output and therefore a loss of light on the workplane. This loss is known as the luminaire dirt depreciation LDD factor and is determined 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 luminaire operates is found as follows. Dirt in the atmosphere comes from two sources—that ed from adjacent air and that generated by work done in the vicinity. Dirt may be classified as adhesive, attracted, or inert, and it may come from intermittent or constant sources. Adhesive dirt clings to luminaire surfaces by its stickiness, whereas attracted dirt is held by electrostatic force. Inert dirt varies in accumulation from practically nothing on vertical surfaces to as much as a horizontal surface holds before the dirt is dislodged by gravity or air circulation. Examples of adhesive dirt are grease from cooking, particles
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Page 16.19
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16.19
from machine operation borne by oil vapor, particles borne by water vapor as in a laundry, and fumes from metal-pouring operations or plating tanks. Examples of attracted dirt are hair, lint, fibers, and dry particles that are electrostatically charged from machine operations. Examples of inert dirt are nonsticky, uncharged particles such as dry flour, sawdust, and fine cinders. 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. Factors 1 to 5 should be assessed and inserted into the spaces in Table 16.3.9 because they are required to describe the conditions of the space. The “Area Adjacent to Task Area” column represents the area separated from but adjacent to the area in which the luminaire operates (which is the “Area Surrounding Task”). The “Filter Factor” column contains the percentages of dirt allowed to from the adjacent atmosphere to the surrounding atmosphere. The “From Adjacent” column indicates the net amount of such dirt that can through. This category might include, for example, an open window with a filter factor of 1.0 (no filtering at all) or an air-conditioning system with a filter factor of 0.1 (90 percent of the dirt is filtered out). The total of all the numbers in the “Subtotal” column is a number up to 60 and can be translated into the applicable atmosphere-dirt category listed at the bottom of the table. c. From the appropriate luminaire maintenance category curve of Figure 16.3.11, the applicable dirt condition curve, and the proper elapsed time in months 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 20 months, the LDD is approximately 0.80. 3. Room surface dirt depreciation (RSDD) factor. The accumulation of dirt on room surfaces reduces the amount of luminous flux reflected and interreflected to the workplane. To take this into , Figure 16.3.12 has been developed to provide RSDD factors for use in calculating maintained average illuminance levels. These factors are determined as follows: a. From one of the five curves in Figure 16.3.12, find the expected dirt depreciation 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 the atmosphere is dirty and room surfaces are cleaned every 24 months, the expected dirt depreciation is 30 percent. b. Knowing the expected dirt depreciation (step a), the type of luminaire distribution, and the room cavity ratio (RCR), determine the RSDD factor from Figure 16.3.12. For example, for a dirt depreciation of 30 percent, a direct luminaire, 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 of 0.95. 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 Function of Operating Position (see page 16.20) 16.3.7
Lamp Lumen Depreciation (see page 16.20)
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Page 16.20
Section Sixteen
16.3.5
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
Percent of vertical lumens
16.3.6 100 90 80 70
0
10
20
30
40
50
60
70
80
90
Operating angle from vertical in degrees (Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
TABLE 16.3.7
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16.3.8 Procedure for Determining Luminaire Maintenance Categories 16.3.8
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
16.21
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Page 16.22
Section Sixteen
16.3.9 Evaluation of Operating Atmosphere TABLE 16.3.9
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
16.3.10 Five Degrees of Dirt Conditions TABLE 16.3.10
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
16.3.11 Luminaire Dirt Depreciation (LDD) Factors for Six Luminaire Categories (I through VI) and for the Five Degrees of Dirtiness as Determined from Figure 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)
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Page 16.23
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16.23
16.3.11
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
TABLE 16.3.12
(Reprinted from the IESNA Lighting Handbook, 9th Edition, 2000, Courtesy of the Illuminating Engineering Society of North America.)
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