Luminous efficacy is an important indicator of energy efficiency, but it doesn’t tell the whole story, particularly with regard to directional light sources.

Due to the directional nature of their light emission, LEDs potentially have higher application efficiency than other light sources in certain lighting applications. Fluorescent and standard “bulb” shaped incandescent lamps emit light in all directions. Much of the light produced by the lamp is lost within the fixture, reabsorbed by the lamp, or escapes from the fixture in a direction that is not useful for the intended application. For many fixture types, including recessed downlights, troffers, and under-cabinet fixtures, it is not uncommon for 40-50% of the total light output of the lamp(s) to be lost before it exits the fixture.

LEDs emit light in a specific direction, reducing the need for reflectors and diffusers that can trap light, so well-designed fixtures and systems using LEDs can potentially deliver light more efficiently to the intended location.

For example, several manufacturers have introduced LED systems for lighting refrigerated display cases in grocery stores. These products are currently based on white LEDs with lower luminous efficacy than the fluorescent lamps they are designed to replace. But because the system design takes advantage of the directional nature of LEDs and their especially good performance under low temperatures, they are demonstrating energy savings of 50% or more compared to standard fluorescent case lights.

Source: EERE