Measuring the Luminous Flux

The flux of a lamp or luminaire can only be measured in specially equipped lighting labs. Since the flux is the total of the lamp's or luminaire's output, an integrating sphere is used that catches all of the emitted light. It's inner surface is painted with a highly reflective, diffuse paint based on Barium Sulphate.

The luminous flux of a lamp will have to be compared to a standard source in order to get an accurate and absolute result. For luminaires, on the other hand, the light output ratio LOR is usually of interest. For this, the measurements are a two-step process: First, the fitting is put in the sphere and the output measured. The result is then compared to the lamp without the fitting.