(Abbr. CU) Portion of rated bare-lamp lumens that exit the fixture and reach the work plane. The CU accounts for the light directly from the luminaire as well as light reflected directly from the luminaire as well as light reflected off the room surfaces. The CU value is used in lighting calculations to estimate light levels or the number of luminaires needed. The CU is determined from a photometric test and is typically published on product catalog sheets in tabular form.

A term used for lighting appliances; the ratio of lumens received on a flat surface to the light output, in lumens, from a lamp; used to evaluate the effectiveness of luminaries in delivering light.

Ratio of luminous flux (lumens) from a luminaire received on the "work plane" [the area where the light is needed] to the lumens emitted by the luminaire.

The ratio of lumens from a luminaire received on the work plane to the total quantity of lumens emitted by the lamps of that luminaire.

In general lighting calculations, the fraction of initial lamp lumens that reach the work plane. CU is a function of luminaire efficiency, room surface reflectances and room shape.

The ratio of lumens from a luminaire received on the work plane to the lumens produced by the lamps alone. (Also called "CU")

A percent of initial lamp lumens that reaches the work plane as determined by surface reflectances, room shape (RCR), and fixture efficiency.

A ratio representing the portion of light emitted by a luminaire in any particular installation that actually gets down to the work plane. The coefficient of utilization thus indicates the combined efficiency of the luminaire, room proportions and room finish reflectances. The ratio of the luminous flux (lumens) from a luminaire is calculated as received on the work-plane to the luminous flux emitted by the luminaire's lamps alone

A coefficient of utilization (CU) is a measure of the efficiency of a luminaire in transferring luminous energy to the working plane in a particular area.