A LED light fixture and a luminous flux monitoring system for a light fixture. The light fixture includes a housing defining an interior space including an interior surface and a transmissive panel. A light source is coupled to the interior surface. The system includes a light sensor coupled to the interior surface and aligned to receive light from the transmissive panel, light source, and/or interior surface. The light sensor is configured to measure luminous flux in the interior space. A controller is coupled to the light source and the light sensor. The controller is configured to determine if a light sensor measurement of luminous flux in the interior space is more or less than a reference value of the luminous flux. If the measurement of luminous flux is less than the reference value, the controller is configured to activate an end-of-life indicator. The reference value equals (total flux−internal ambient flux)×depreciation factor.