This test unit has been designed to generate a wide range of optical output signals. Flame sensors for fire detection and flame monitoring applications can be activated and tested. Most optical flame sensors respond to Ultra Violet (UV) and or InfraRed (IR) radiation emitted from flames during combustion. Many sensors also use flame flicker techniques to distinguish between flames and other optical false sources. The test unit simulates the flickering flame signal by modulating the output of a filament lamp. The thermal time constant of a filament lamp prevents the generation of a perfect flame flicker signal. The slow response of the filament lamp will mean that some flame sensors many require more time to activate under test than they would with a real flame. The unit is intended for service engineers to use, when performing commissioning and routine maintenance.