In this tutorial the term photosensor refers to a device that contains the following elements:
- a light-sensitive photocell,
- input optics,
- an electronic circuit needed to convert the photocell signal into an output control signal, and
- a device housing and mounting hardware.
The actual device might be a photodiode, a phototransistor, or a photoconductive cell. It is important to make a distinction between a photocell and a complete photosensor device. The term photocell is defined in this tutorial
as the light-sensitive component within the photosensor.
Although many of the principles of operation and performance characteristics of photosensors are relevant for all types of photosensor lighting control, the emphasis of this tutorial is on closed loop systems with fluorescent lamp luminaires.