Tunnel safety relies on accurately measuring luminance – the perceived light available for drivers to drive safely – the main control variable for the tunnel lighting.
The requirements for tunnel lighting are determined by the nature of the human eye. How well the eye recognises vehicles and other obstacles in a tunnel depends on the lighting and visibility as well as the reflection characteristics of the road surface and the tunnel walls. Tunnel lighting needs to be adapted to these environmental conditions.
The tunnel lighting must be controlled so that users, both during the day and by night, can approach, pass through and exit the tunnel without changing direction or speed with a degree of safety equal to that on the approach road. Especially the lighting of a tunnel entrance should be adequate to avoid the “black hole effect” when a driver enters the tunnel.
Luminance is the measure representing what a human being perceives as brightness and as such is the main control variable for the tunnel lighting.
The luminance photometer comes with a zoom lens that is focused to measure the relevant area. Light from this area through the lens is directed to the photo element detecting its intensity. The integrated evaluation unit then calculates the luminance and provides it through the analogue output(s).