A hall of 30 metres by 15 metres with a ceiling height of 5 metres is to be provided with a general illumination of 120 lumens/m2. Taking a coefficient of utilisation of 0.5 and depreciation factor of 1.4 , determine the number of fluorescet tubes required, their spacing, mounting height and total wattage.Take luminous efficiency of fluorescent tube as 40 lumens per watt for 80 watt tubes.
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Given A hall of 30 metres by 15 metres with a ceiling height of 5 metres is to be provided with a general illumination of 120 lumens/m2. Taking a coefficient of utilisation of 0.5 and depreciation factor of 1.4 , determine the number of fluorescet tubes required, their spacing, mounting height and total wattage.Take luminous efficiency of fluorescent tube as 40 lumens per watt for 80 watt tubes.
- Given area A = 30 x 15 = 450 m^2, E = 120 lm/m^2, ƞ = 0.5, p = 1.4
- So φ = EA / ƞ p
- = 120 x 450 / 0.5 x 1.4
- = 54000 / 0.7
- Or φ = 77142.8 lm
- Now flux emitted per tube will be 80 x 40 = 3200 lm
- Therefore number of tubes required will be 77142.8 / 3200
- = 24
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