The coefficient of utilization (CU) is a measure used to assess the efficiency of a luminaire in delivering light to a specific area, such as a work plane or canopy. It is expressed as a ratio, representing the amount of light that reaches the desired area compared to the total light emitted by the lamps within the luminaire. To calculate the coefficient of utilization, various factors are taken into account. These include the room utilization factor (utilance), which considers the reflective properties of the room surfaces, and the luminaire efficiency, which accounts for the effectiveness of the luminaire in directing light towards the desired area.