An unshielded lamp of 250W is hung at 2 m below the ceiling. The lamp emits light uniformly in all directions and its luminous efficacy is 70 lm/W. The height of the room is 5m. Determine:-
(i) The luminous flux emitted by the lamp
(ii) The luminous intensity of the lamp
(iii) The illuminance on the floor just down the lamp due to direct illumination from the lamp
luminous flux / luminous intensity / illuminance?
2015-10-22 5:17 pm
回答 (1)
2015-10-24 10:01 am
✔ 最佳答案
(i) The luminous flux emitted by the lamp F = 250 w * 70 lm/w = 17500 lm
(ii) The luminous intensity of the lamp
I = F/4π = 17500 / 4π = 1392.6 candles
(iii) The illuminance on the floor just down the lamp due to direct
illumination from the lamp
E = I/r^2
= 1392.6 / (5-2)^2
= 1392.6 / 9
= 154.73 lm/m^2
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