Two aspects of energy efficiency are important to consider: the efficiency of the LED device itself (source efficacy); and how well the device and fixture work together in providing the necessary lighting (luminaire efficacy). How much electricity is used to provide the intended lighting service depends not only on the LED device, but on the lighting fixture design. Because they are sensitive to thermal and electrical conditions, LEDs must be carefully integrated into lighting fixtures. Poorly designed fixtures using even the best LEDs may be no more efficient than incandescent lighting. Conversely, a well-designed LED-based refrigerated display case light that takes advantage of the directional nature of LEDs may use only about half the total watts of a linear fluorescent system to provide the necessary lighting, even though the LEDs have lower source efficacy than the linear fluorescent lamps.

Conventional Lighting Compared to Typical LED Efficacy in 2010
Product Type Typical Luminous Efficacy (in lm/W)
LED cool white package 130
LED warm white package 93
LED A19 lamp (warm white) 64
LED PAR38 lamp (warm white) 52.5
High intensity discharge (high watt)
Lamp and ballast
Linear fluorescent
Lamp and ballast
High intensity discharge (low watt)
Lamp and ballast
Compact fluorescent lamp 63
Halogen 20
Incandescent 15

Source: 2011 DOE SSL Multi-Year Program Plan