Lumen Method Details. Because of the ease of application of the lumen method which yields the average The lumen method is based on the definition of a footcandle, which equals one lumen per square fg Form. illumination in a room, it is usually employed for larger areas, where the illumination is substantially ur footcandle lumen striking an area (107.2) quare feet of area In order to take into consideration such factors as dirt on the luminaire, general depreciation in lume output of the lamp, and so on, the above formula is modified as follows footcandle lamps/ luminaire× lumens/p×CU×LLF (1073) area/luminaire ethod, the following key steps should be taken a. Determine the required level of illuminance. b. Determine the coefficient of utilization(CU)which is the ratio of the lumens reaching the working plane to the total lumens generated by the lamps. This is a factor that takes into account the efficiency and the distribution of the luminaire, its mounting height, the room proportions, and the reflectances of the walls, ceiling, and floor. Rooms are classified according to shape by 10 room cavity numbers. The cavity ratio can be calculated using the formula given in Eq. (107. 1). The coefficient of utilization is selected from tables prepared for various luminaires by manufacturers C. Determine the light loss factor (LLF). The final light loss factor is the product of all the contributing loss factors. Lamp manufacturers rate filament lamps in accordance with their output when the lamp is new; vapor discharge lamps(fluorescent, mercury, and other types )are rated in accordance with their output after 100 hr of burning d. Calculate the number of lamps and luminaires required: footcandles×area no of lamps (1074) lumens/p× CU x LLF no of lamps no of luminaires- lamps/luminair (1075) e. Determine the location of the luminaire--luminaire locations depend on the general architecture, size ys, type of luminaire, posi Point-by-Point Method. Although currently light computations emphasize the zonal cavity method, there is still considerable merit in the point-by-point method. This method lends itself especially well to calculating the illumination level at a particular point where total illumination is the sum of general overhead lighting and supplementary lighting. In this method, information from luminaire candlepower distribution curves must be applied to the mathematical relationship. The total contribution from all luminaires to the illumination level on the task plane must be summed. Direct Illumination Component. The angular coordinate system is most applicable to continuous rows of fluorescent luminaires. Two angles are involved: a longitudinal angle a and a lateral angle B. Angle a is the angle between a vertical line passing through the seeing task (point P)and a line from the seeing task to the end of the rows of luminaires. Angle a is easily determined graphically from a chart showing angles a and p e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Lumen Method Details. Because of the ease of application of the lumen method which yields the average illumination in a room, it is usually employed for larger areas, where the illumination is substantially uniform. The lumen method is based on the definition of a footcandle, which equals one lumen per square foot: (107.2) In order to take into consideration such factors as dirt on the luminaire, general depreciation in lumen output of the lamp, and so on, the above formula is modified as follows: (107.3) In using the lumen method, the following key steps should be taken: a. Determine the required level of illuminance. b. Determine the coefficient of utilization (CU) which is the ratio of the lumens reaching the working plane to the total lumens generated by the lamps. This is a factor that takes into account the efficiency and the distribution of the luminaire, its mounting height, the room proportions, and the reflectances of the walls, ceiling, and floor. Rooms are classified according to shape by 10 room cavity numbers. The cavity ratio can be calculated using the formula given in Eq. (107.1). The coefficient of utilization is selected from tables prepared for various luminaires by manufacturers. c. Determine the light loss factor (LLF). The final light loss factor is the product of all the contributing loss factors. Lamp manufacturers rate filament lamps in accordance with their output when the lamp is new; vapor discharge lamps (fluorescent, mercury, and other types ) are rated in accordance with their output after 100 hr of burning. d. Calculate the number of lamps and luminaires required: (107.4) (107.5) e. Determine the location of the luminaire—luminaire locations depend on the general architecture, size of bays, type of luminaire, position of previous outlets, and so on. Point-by-Point Method. Although currently light computations emphasize the zonal cavity method, there is still considerable merit in the point-by-point method. This method lends itself especially well to calculating the illumination level at a particular point where total illumination is the sum of general overhead lighting and supplementary lighting. In this method, information from luminaire candlepower distribution curves must be applied to the mathematical relationship. The total contribution from all luminaires to the illumination level on the task plane must be summed. Direct Illumination Component. The angular coordinate system is most applicable to continuous rows of fluorescent luminaires. Two angles are involved: a longitudinal angle a and a lateral angle b. Angle a is the angle between a vertical line passing through the seeing task (point P) and a line from the seeing task to the end of the rows of luminaires. Angle a is easily determined graphically from a chart showing angles a and b footcandle lumen striking an area square feet of area = footcandle lamps/luminaire lumens/lp CU LLF area/luminaire = ¥ ¥ ¥ no. of lamps footcandles area lumens/lp CU LLF = ¥ ¥ ¥ no. of luminaires no. of lamps lamps/luminaire =
for various combinations of V and H. Angle B is the angle between the vertical plane of the row of luminaires and a REFERENCE tilted plane containing both the seeing task and the luminaire or row of luminaires. Figure 107.2 shows how angles a and B are defined. The direct illumination component for each luminaire or row of luminaires is determined by referring to the table of direct illumination components for the specific luminaire. The direct illumination components are based on the assumption that the luminaire is mounted 6 ft above the seeing task. If this mounting height is other than 6 ft, the v rect illumination component shown in Table 107.5 must be multiplied by 6/V where Vis the mounting height above the task. Thus the total direct illumination component would VERTICAL PLANE be the product of 6/V and the sum of the individual direct illumination components of each row. Reflected Illumination Components on the Horizontal FIGURE 107.2 Definition of angular coordinate sys- Surfaces. This is calculated in exactly the same manner as tems for direct illumination component. ne average illumination using the lumen method, except that the reflected radiation coefficient(rrc) is substituted for the coefficient of utilization. lamps/ uminaire x lumens/lp×RRC×LLF RH (1076) area/luminaire where RRC= LCw RPM(LCcc -LCw), LCw=wall luminance coefficient, LCac= ceiling cavity luminance coefficient, and RPM room position multiplier. The wall luminance coefficient and the ceiling cavity luminance coefficient are selected for the appropriate room cavity ratio and proper wall and ceiling cavity reflectances from the table of luminance coefficients in the same manner as the coefficient of utilization. The room position multiplier is a function of the room cavity ratio and of the location in the room of the point where the illumination is desired. Table 107. 6 lists the value of the RPM for each possible location of the part in the rooms of all room cavity ratios Figure 107.3 shows a grid diagram that illustrates the method of designating the location in the room by a Reflected Illumination Components on the Vertical Surfaces. To determine illumination reflected to vertical surfaces, the approximate average value is determined using the same general formula, but substituting WRRC all reflected radiation coefficient) for the coefficient of utilization lamps/ luminaire x lumens/lp×WRRC×LLF area/luminaire(on work plane) (107.7) WRRC E all luminance coefficient WDRC (1078) average wall reflectance where WDRC is the wall direct radiation coefficient, which is published for each room cavity ratio together with a table of wall luminance coefficients(see Table 107.5 for a specific type of luminance) e 2000 by CRC Press LLC
© 2000 by CRC Press LLC for various combinations of V and H. Angle b is the angle between the vertical plane of the row of luminaires and a tilted plane containing both the seeing task and the luminaire or row of luminaires. Figure 107.2 shows how angles a and b are defined. The direct illumination component for each luminaire or row of luminaires is determined by referring to the table of direct illumination components for the specific luminaire. The direct illumination components are based on the assumption that the luminaire is mounted 6 ft above the seeing task. If this mounting height is other than 6 ft, the direct illumination component shown in Table 107.5 must be multiplied by 6/V, where V is the mounting height above the task. Thus the total direct illumination component would be the product of 6/V and the sum of the individual direct illumination components of each row. Reflected Illumination Components on the Horizontal Surfaces. This is calculated in exactly the same manner as the average illumination using the lumen method, except that the reflected radiation coefficient (RRC) is substituted for the coefficient of utilization. (107.6) where RRC = LCW + RPM (LCCC – LCW), LCW = wall luminance coefficient, LCCC = ceiling cavity luminance coefficient, and RPM = room position multiplier. The wall luminance coefficient and the ceiling cavity luminance coefficient are selected for the appropriate room cavity ratio and proper wall and ceiling cavity reflectances from the table of luminance coefficients in the same manner as the coefficient of utilization. The room position multiplier is a function of the room cavity ratio and of the location in the room of the point where the illumination is desired. Table 107.6 lists the value of the RPM for each possible location of the part in the rooms of all room cavity ratios. Figure 107.3 shows a grid diagram that illustrates the method of designating the location in the room by a letter and a number. Reflected Illumination Components on the Vertical Surfaces. To determine illumination reflected to vertical surfaces, the approximate average value is determined using the same general formula, but substituting WRRC (wall reflected radiation coefficient) for the coefficient of utilization: (107.7) where (107.8) where WDRC is the wall direct radiation coefficient, which is published for each room cavity ratio together with a table of wall luminance coefficients (see Table 107.5 for a specific type of luminance). FC lamps/luminaire lumens/lp RRC LLF area/luminaire RH = ¥ ¥ ¥ FC lamps/luminaire lumens/lp WRRC LLF area/luminaire (on work plane) RV = ¥ ¥ ¥ WRRC wall luminance coefficient average wall reflectance = – WDRC FIGURE 107.2 Definition of angular coordinate systems for direct illumination component
TABLE 107.5 Direct Illumination Components for Category III Luminaire(Based on F40 Lamps Producing 3100 Lumer Direct Illumination Components 515253545556575515253545556575 Vertical Surface Illumination Footcandles at a Vertical Surface Illumination Footcandles at a Point on a plane parallel to luminaires Point on a Plane Perpendicular to Luminaires 93.3 1.85.07.07.76.63.81.52 84.3271.13 1297.7 3.2.512.6 92.1.6 3019,5a212121m5112 76.81.4 232267 17 352 26.723.819.714.98.74.3 1941347.5 27.124.220.115.39.14.71.1 FC. at a Point on Work plane Category Ill 10.69.57.6 1.616.0984.01.1 9541.5 41.838.1 .76.72.0 45.241.334.8 6792.62 46.943.036.428318.98.93.23 43 47.543.737.028.8194933.54 For T-10 Lamps.=CU×1.02 Luminance Coefficients for 20% Effective Floor Cavity Reflectance Ceiling Cavity WDRC RCR Wall Luminance coefficients eiling Cavity Luminance Coefficients 127 115182 .115 .202 161088 .158077145 72.130066.190.139113085021016 072 35110082021 14910 .141068130064116059 18013 107080020 107.2 Factors Affecting industrial illumination asic definitions Illuminance. luminance is the density of luminous lux on a surface expressed in either footcandles Luminance(or photometric brightness). Luminance is the luminous intensity of a surface in a given direction of projected area of the sur candelas per unit area or in lumer unit area Reflectance. Reflectance is the ratio of the light reflected from a surface to that incident upon it. Reflection may be of several types, the most common being specular, diffuse, spread, and mixed Glare. Glare is any brightness that causes discomfort, interference with vision, or eye fatigue e 2000 by CRC Press LLC
© 2000 by CRC Press LLC 107.2 Factors Affecting Industrial Illumination Basic Definitions Illuminance. lluminance is the density of luminous lux on a surface expressed in either footcandles (lumens/ft2 ) or lux (lx) (lux = 0.0929 fc). Luminance (or photometric brightness). Luminance is the luminous intensity of a surface in a given direction per unit of projected area of the surfaces, expressed in candelas per unit area or in lumens per unit area. Reflectance. Reflectance is the ratio of the light reflected from a surface to that incident upon it. Reflection may be of several types, the most common being specular, diffuse, spread, and mixed. Glare. Glare is any brightness that causes discomfort, interference with vision, or eye fatigue. TABLE 107.5 Direct Illumination Components for Category III Luminaire (Based on F40 Lamps Producing 3100 Lumens) Direct Illumination Components 8 5 15 25 35 45 55 65 75 5 15 25 35 45 55 65 75 Vertical Surface Illumination Footcandles at a Vertical Surface Illumination Footcandles at a µ Point on a Plane Parallel to Luminaires Point on a Plane Perpendicular to Luminaires 0–10 .9 2.6 3.6 3.9 3.3 1.9 .7 .1 .9 .8 .7 .5 .3 .1 — — 0–20 1.8 5.0 7.0 7.7 6.6 3.8 1.5 .2 3.6 3.2 2.7 1.9 1.2 .5 .1 — 0–30 2.6 7.2 10.1 11.3 9.8 5.7 2.3 .3 7.7 7.0 5.8 4.3 2.7 1.1 .3 — 0–40 3.2 9.0 12.8 14.5 12.9 7.7 3.2 .5 12.6 11.6 9.7 7.5 4.9 2.1 .6 — 0–50 3.7 10.3 14.9 17.1 15.7 9.6 4.3 .7 17.8 16.6 14.2 11.2 7.7 3.4 1.1 .1 0–60 4.0 11.2 16.3 18.8 17.6 11.3 5.5 1.0 22.6 21.2 18.4 14.7 10.4 5.1 1.9 .2 0–70 4.1 11.6 17.0 19.8 18.9 12.7 6.8 1.4 26.2 24.7 21.8 17.8 13.1 7.2 3.2 .3 0–80 4.1 11.7 17.3 20.2 19.4 13.3 7.4 1.9 28.2 26.7 23.8 19.7 14.9 8.7 4.3 .8 0–90 4.1 11.7 17.3 20.2 19.4 13.4 7.5 2.0 28.6 27.1 24.2 20.1 15.3 9.1 4.7 1.1 F.C. at a Point on Work Plane Category III 0–10 10.6 9.5 7.6 5.5 3.3 1.3 .3 — 0–20 20.6 18.5 14.9 10.9 6.6 2.6 .7 — 0–30 29.4 26.5 21.6 16.0 9.8 4.0 1.1 — 0–40 36.5 33.1 27.4 20.6 12.9 5.4 1.5 — 0–50 41.8 38.1 31.9 24.3 15.7 6.7 2.0 .1 0–60 45.2 41.3 34.8 26.8 17.6 7.9 2.6 .2 0–70 46.9 43.0 36.4 28.3 18.9 8.9 3.2 .3 0–80 47.4 43.6 36.9 28.8 19.4 9.3 3.5 .4 2 T-12 Lamps—Any Loading 0–90 47.5 43.7 37.0 28.8 19.4 9.3 3.5 .4 For T-10 Lamps—CU 3 1.02 Luminance Coefficients for 20% Effective Floor Cavity Reflectance Reflectances Ceiling Cavity 80 50 10 80 50 10 Walls 50 30 50 30 50 30 50 30 50 30 50 30 WDRC RCR Wall Luminance Coefficients Ceiling Cavity Luminance Coefficients .281 1 .246 .140 .220 .126 .190 .109 .230 .209 .135 .124 .025 .023 .266 2 .232 .127 .209 .115 .182 .102 .222 .190 .130 .113 .024 .021 .245 3 .216 .115 .196 .105 .172 .095 .215 .176 .127 .105 .024 .020 .226 4 .202 .102 .183 .097 .161 .088 .209 .164 .124 .099 .023 .019 .212 5 .191 .097 .173 .090 .154 .082 .204 .156 .121 .094 .023 .018 .196 6 .178 .090 .163 .084 .145 .076 .200 .149 .118 .090 .022 .017 .182 7 .168 .083 .153 .078 .136 .071 .194 .144 .115 .087 .022 .017 .170 8 .158 .077 .145 .072 .130 .066 .190 .139 .113 .085 .021 .016 .159 9 .150 .072 .138 .068 .123 .062 .185 .135 .110 .082 .021 .016 .149 10 .141 .068 .130 .064 .116 .059 .180 .131 .107 .080 .020 .016