TE Enriched Sample (E)

Lighting 1 30 Summary Key Ideas Light power and emission • Luminous flux Φ measures the brightness of a source. Its unit is the lumen (lm). • Luminous efficacy input power luminous flux = • Emission of light is the result of atom transitions from higher energy levels to lower energy levels. energy energy absorption EM waves energy End-use energy efficiency • Definition: E E 100 in out # h = • An electrical appliance with higher end-use energy efficiency can convert more electricity into useful energy. • Energy labels can tell us about the efficiency of some electrical appliances. • Energy saving devices can cut down unnecessary electricity usage. E out E in heat Types of lighting • Comparison of various lighting devices incandescent lamp gas discharge lamp LED lamp size medium large small light source hot filament phosphor (fluorescent coating) two layers of semiconductors working temperature high medium low price low medium high lifetime short medium long efficacy low medium high major advantage cheap price–efficacy balance high efficacy major disadvantage low efficacy mercury content heavy-metal content Illuminance • Measures how much light is incident on a surface • Illuminance E A U = • Unit: lux (lx, 1 lx = 1 lm m −2 ) Inverse-square law • Illuminance on a spherical surface E r 4 0 2 r U = 2 r 3 r r S DSE Level-up Companion A revision exercise is provided for helping Ss to grip the key points. See Level-up Task 81A . 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.