JGJ / t119-2008, the terminology standard for building lighting, gives the definition of utilization coefficient, that is, the ratio of the luminous flux projected onto the reference plane to the luminous flux of the light source in the lighting device. It can be expressed by formula:
U= φ 1/ φ 2=（ φ 1d+ φ 1r）/ φ two


Where,
φ 1 -- luminous flux projected onto the reference plane, including direct luminous flux φ 1D and reflected luminous flux φ 1r；


φ 2 -- luminous flux of light source.


The LED has good directivity, and its luminous flux projected onto the reference plane (generally the working surface) is relatively large, which is not as large as the loss of traditional light sources and lamps in the process of light transmission, and meets certain conditions φ 1D approach φ 2. Therefore, there is a case where u > 1.


The necessary conditions for the utilization factor to be greater than or equal to 1 are as follows:


1) Direct lamp, downward luminous flux up to 100%, lamp efficiency is high;


2) It is difficult for narrow beam and wide beam to have high utilization coefficient;


3) The ceiling, wall and ground have good reflection performance;


4) The room space ratio is small, or the room shape index is large, and the installation height of lamps is not high.


Therefore, the utilization coefficient of LED lamp is greater than 1. Therefore, LED lamp is more energy-saving than traditional lighting source and lighting device.