In our role as Meter Administrator we have visibility of the different PECUs used on the traffic signal installations by our customers. These codes identify the type of photocell used to control the bright/dim function in traffic signals. I have never really understood if there is an optimum lux level range for a set of traffic signals, we have a very wide variation across our customer base:
The higher lux cells mean that the traffic signals are dim for longer (=lower annual energy use) than the lower lux cells that turn to bright earlier in the morning. But energy is probably not the key driver, the key driver is safety to ensure they are bright enough to be seen at dawn/dusk whilst not dazzling the driver by being bright too late into dusk.
Is there any official industry guidance or advice on the appropriate lux levels to use?