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Coefficient of utilization
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<p>A coefficient of utilization (CU) is a measure of the efficiency of a <a href="/facts/Luminaire/vjgU4z1f">luminaire</a> in transferring <a href="/facts/Luminous_energy/hlWJ3tRy">luminous energy</a> to the working plane in a particular area. The CU is the ratio of <a href="/facts/Luminous_flux/Sfya3RXh">luminous flux</a> from a luminaire incident upon a work plane to that emitted by the lamps within the luminaire. As a ratio, the coefficient of utilization is unitless. </p><p>For example, some of the light emitted by a luminaire may exit away from the desired plane and is therefore wasted. A CU measures the light actually reaching the desired plane as a percentage of the total light produced by the fixture. The value for direct lighting varies from 0.2 to 0.5 while that of indirect lighting varies from 0.1 to 0.3 </p>