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A complete lighting unit including lamp(s), ballast(s) (when applicable), and the parts designed to distribute the light, position and protect the lamps, and connect to the power supply.

Luminaire efficiency is the ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein; expressed as a percentage.

Luminaire efficacy is the total light output (lm) provided by the luminaire divided by the total wattage (W) drawn by the fixture, expressed in lumens per watt (lm/W).

Directionality of luminaires

Luminaires designed to take advantage of LED directionality (see solid state lighting) can be more energy efficient than those using traditional light sources. For example, most incandescent and fluorescent lamps emit light in all directions. In a typical kitchen undercabinet fixture, for example, only about half the light produced by the lamp actually comes out of the fixture. LED undercabinet luminaires can be designed to direct light to the horizontal countertop and vertical backsplash surfaces, using less total energy than other sources.

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