TE Enriched Sample (E)

Summary 31 Point light source and oblique incidence • At X , cos E r 4 X 2 $ r i U = ; ; Ö spreading Ö oblique incidence where i is the angle of incidence and cos i = d / r . d r X θ point light source θ Lambert’s cosine law • For a light beam shining on the surface at an angle θ , E = E 0 cos i A 0 θ A 0 A 0 cos θ a b A 0 Keywords compact fluorescent lamp 緊湊式熒光燈 end-use energy efficiency 最終能源效益 energy level 能階 fluorescent tube lamp 熒光燈 gas discharge lamp 氣體放電燈 illuminance 照明度 incandescent lamp 白熾燈 inverse-square law 平方反比定律 Lambert ’ s cosine law 朗伯餘弦定律 light emitting diode 發光二極管 lumen 流明 luminous efficacy 發光效率 luminous flux 光通量 lux 勒克斯 p–n junction p–n 結 Common Mistakes • 4 wavelength / 10 –7 m wavelength / 10 –7 m intensity intensity incandescent lamps gas discharge lamps similar for all lighting devices 5 6 7 4 5 6 7 Incandescent lamps produce a continuous spectrum, but gas discharge lamps and LED lamps do not. • quantity luminous flux illuminance quantity luminous flux illuminance unit lux (lx) lumen (lm) unit lumen (lm) lux (lx) Do not confuse the units of luminous flux, luminous efficacy and illuminance. Luminous flux is measured in lumens (lm). Luminous efficacy is measured in lm W −1 . Illuminance is measured in lux (lx). Sample © United Prime Educational Publishing (HK) Limited, Pearson Education Asia Limited 2023 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publishers.