Question

It is required to provide an illumination of 100 lux in a workshop hall 40 m x 10 m and efficiency of lamp is 14 lm/W for 750 W lamp. Calculate the number and rating of lamps when trusses are provided at mutual distance of 5 m. Take coefficient of utilization as 0.4 and maintenance factor as 0.8.

ANS [12 lamps]

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Answer 1

Answer -

   Area of workshop Hall A = 40 x 10 = 400 m²

   Illumination E = 100 lux

   Total lumens = A x E = 400 x 100 = 40000

Coefficient of Utilization = 0.4

   Maintenance factor = 0.8

Now,

   Gross lumens required = Total lumens / (Coefficient of Utilization) x (Maintenance factor)

     Gross lumens required = 40000/ (0.4 x 0.8)

     Gross lumens required = 125000

Now,

Total Wattage required = Gross lumens required / Efficiency of lamp

     Total Wattage required = 125000 / 14

     Total Wattage required = 8928.57 W

Now,

Number of lamps required = Total wattage required / Rating of lamp

Number of lamps required = 8928.57 / 750

Number of lamps required = 11.9 12

Hence, total number of lamps required is 12 each of 750 W.