Apparatus, method and system for monitoring and maintaining light levels at target area for lighting system

An apparatus for sensing lumen depreciation from a plurality of lighting fixtures comprising:

• a. a light quantity sensor adapted to measure light quantity of the plurality of lighting fixtures externally of the lighting fixtures;
• and
• b. a light quantity sensor circuit operatively connected to the light quantity sensor adapted to generate a signal or alarm if measured light quantity by the light quantity sensor falls below a reference quantity for a predefined period of time.

A system of sensing lumen depreciation from a plurality of lighting fixtures adapted to collectively illuminate a target area comprising:

• a. a plurality of light sources in the lighting fixtures, each light source having an LLD characteristic and each fixture having at least one optical surface;
• b. at least one light quantity sensor external of the lighting fixtures adapted to measure light quantity of at least one of the lighting fixtures relative to a reference quantity, the at least one light quantity sensor configured to restrict the light quantity measurement to a predetermined range of wavelengths and to a predetermined field of view relative to the target area;
• c. a circuit operatively connected to each light quantity sensor adapted to generate a signal if the measured light quantity differs from the reference quantity by a predetermined amount or more.