LED Technology — Revision Notes

⚡ 30-Second Revision

W: power; lm: flux; lux: flux/area. Efficacy = lm/W. Nine watts for 900 lumens gives 100 lm/W. Six watts saved for 1,000 hours gives 6 kWh. Blue-LED Nobel: 2014.

2-Minute Revision

An LED emits through semiconductor processes, while a luminaire includes drivers, optics and thermal design. White lighting can use spectral combinations, including blue emission with phosphor conversion.

Source and whole-unit efficacy differ. Colour temperature describes appearance; colour rendering concerns objects under the light. Equal 900-lumen lamps at nine and fifteen watts have efficacies of 100 and sixty lm/W.

Under equal operating time, their energy difference follows power multiplied by hours, not wattage alone.

5-Minute Revision

Calculate efficacy for 900 lumens at nine and fifteen watts. Then calculate average illuminance when 600 lumens actually reach two square metres. For five hours daily over 200 days, calculate each lamp's energy use and the difference. Explain why the result does not establish a money saving without a tariff. Finish by distinguishing colour temperature from physical temperature and emitter performance from complete-unit performance.

Vyyuha Quick Recall

Power, flux, surface, time: watts, lumens, lux and kilowatt-hours describe different parts of the lighting service.