Do you dim your traffic signals?

In our role as Meter Administrator we have visibility of the different PECUs used on traffic signal installations by our customers to switch between bright (daytime) and dim (night time). But what is the optimum lux level range for a set of traffic signals?

The higher lux photocells 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 ensuring they are bright enough to be seen in sunlight whilst not dazzling the driver by being too bright during the night.

Is there any official industry guidance or advice on the appropriate lux levels to use?  Please contact us with any insight