Light Output Ratio (LOR) is the ratio of the luminous flux leaving a luminaire to the luminous flux produced by its lamp or light source, expressed as a percentage. It describes optical losses within the luminaire. For integrated LED products, operational lumens and luminous efficacy are often more useful comparison values. An LOR of 100% would mean that all source lumens leave the luminaire, while a lower value indicates losses in reflectors, lenses, diffusers, or other components. LOR does not show where the outgoing light is directed or whether it is useful for the task. Light distribution and operational conditions remain essential to product comparison.