Assuming a suitable space- height ratio, a utilization factor of 0.5, a lamp efficiency of 14 lumens per watt and a candle power depreciation of 20%, estimate the number, rating and disposition of lamps.Īrea to be illuminated, A = 72 x 15 = 1,080 m 2 The lamps are required to be hung 4 m above the work bench. 7.45.Īn illumination on the working plane of 75 lux is required in a room 72 m x 15 m in size. Total lumens required = A x E = 1,000 x 80 = 80,000Ĥ2 lamps of 150 W rating in 2 rows, each row having 21 lamps, can be used giving spacing of 4.76 m in length and 5 metres in width.ĭisposition of lamps is shown in Fig. Assume that the depreciation factor is 0.8, coefficient of utilization is 0.4 and efficiency of the lamp is 40 lumens/watt.Īrea to be illuminated, A = 100 x 10 = 1,000 m 2 Calculate the number, location and the wattage of the units to be used. Total lumens required = E x A = 200 x 160 = 32,000 lumensĪ minimum illumination of 80 lumens/m 2 is required in a factory shed of 100 m x 10 m. Calculate the number of lamps required to illuminate the whole area if the lumen output of the lamp selected is 3,000 lumens. The utilization and maintenance factors are 0.74 and 0.8 respectively. It is employed only in some special problems, such as flood lighting, yard lighting etc.Ī small assembly shop 16 m long, 10 m wide and 3 m up to trusses is to be illuminated to a level of 200 lux. This method is not much used because of its complicated and cumbersome applications. If two and more than two lamps are illuminating the same working plane, the illumination due to each can be calculated and added. If a polar curve of lamp and its reflector giving candle powers of the lamp in different directions is known, the illumination at any point within the range of the lamp can be calculated from the inverse square law. This method is applicable where the illumination at a point due to one or more sources of light is required, the candle powers of the sources in the particular direction under consideration being known. Point to Point or Inverse-Square Law Method: This is merely the inverse of the maintenance factor and is defined as the ratio of the initial metre- candles to the ultimate maintained metre-candles on the working plane.
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