With this type of flame supervision, the radiation of oil flames in the visible light spectrum is used for generating the flame signal.

The light-sensitive element is a photoresistor.

When there is no light, the detector′s resistance is in the MΩrange.

The resistance drops as the intensity of illumination increases (kΩrange).

In contrast to the selenium photocell of the RAR... detectors, glowing firebrick in the combustion chamber can be detected.