Excess Gain (function reserve) in photo electric sensors
Excess gain is a unitless factor which indicates how much more light reaches the receiver than is necessary for function of the sensor.
Generally, it is expressed as a relative amount, with the required light level = 1.
The higher the excess gain is, the more reliable is the object detection. The reference material is white, with 90% remission.
If the target is darker, e.g. gray or black, the excess gain is lower and the curve will be different.
Higher excess gain is recommended for contaminated environments.