Electric Light Sources You likely won’t be able to illuminate a space through daylight alone all the time, so you’ll have to learn to efficient artificial light design. Light sources are the different kinds of lamps, bulbs, or other devices used to create artificial light. The choice of light source is v ery important, both for visual comfort and for energ y efficiency. Roughly 1/3 of an average US commercial building' s energy use is lighting . Artificial light sources are measured not only by their visual comfort characteristics (brightness, color temperature, color rendering index, and light distribution), but also their efficacy--that is, their effectiveness at converting electricity into light. Lighting EfficiencyCommon Light Sources Selecting a LampLighting Efficiency The energy efficiency of artificial lights are measured b y "luminous efficacy", the ratio of luminous flux coming out (in Lumens) to electricity and/or heat going in (in Watts). Energy that does not emerge as light emerges as h eat. Note that lighting efficiency is a function of b oth light source itselfand the fixture housing it. CategoryType Combustioncandlegas mantleIncandescent tungsten incandescenttungsten glass halogenFluorescent Compact fluorescentT8 tubeT5 tubeLight-emitting diodeLED screw base lamp (120 V) Gas dischargemetal halidelow pressure sodiumLuminous efficacy of various light sources (from Wikipedia )