Fixture efficiency measures how effectively a lighting fixture converts electrical energy into visible light. It is a crucial metric used in the lighting industry to evaluate the efficiency of a lighting fixture in terms of its ability to produce light output while minimizing energy losses. This efficiency is typically calculated by dividing the luminous efficacy, which is a measure of how efficiently a light source produces visible light, by 683 lm/W, representing the maximum value of luminous efficacy that a light fixture can achieve.