Total luminous flux is the spatially integrated, photopically weighted, total light output from a lamp. Total luminous flux is the most important parameter for non-directional, general lighting products.
For directional lamps, such as reflector lamps, intensity and beam angle are the most important parameters. The lamp total luminous flux divided by the lamp electrical power is the luminous efficacy (lm/W) of a lamp.
The most common method for measuring the total luminous flux of lamps is using an integrating sphere photometer employing V (lambda) corrected photometer or spectrometer. The reading from the detection system is compared to a similar reading obtained from a calibrated standard lamp of known output, commonly referred to as the “comparison method”. The results of this comparison determine the light output of the test lamp.