The United States Department of Energy had a recent article on Led Lights and Luminous Efficacy. The article’s emphasis is on how certain applications such as recessed lighting benefit from what the department of energy terms ” Application Efficiency”
Here is the article:
“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, like an undercabinet light can deliver light more efficiently to the intended location.
While there is no standard definition of application efficiency, we use the term here to denote an important design consideration: that the desired illuminance level and lighting quality for a given application should be achieved with the lowest practicable energy input. Light source directionality and intensity may result in higher application efficiency even though luminous efficacy is lower relative to other light sources.”