Screen brightness is measured in NITs, so 1 Nit = 1 Candela per sqm. Typically, the minimum requirement would be 5000 Nits for outdoor and 800 Nits for indoor. However it’s not always about the brightness, it can also be about getting the contrast right. An Auto-brightness (ABC) controller is important for all outdoor and increasingly for indoor screens. If we can fit a sensor it will be linked back to the LED controller which will automatically control the brightness. It is often a requirement made by planning offices these days, and they will usually specify brightness levels.
ABCs work over time, so it won’t adjust if car temporarily points its headlights directly at it. There will be an average reading over say 10 minutes.
Every screen in Piccadilly Circus has an ABC controller too, but there is an element of competitiveness whereby none of the displays wanted to be duller than its neighbour, so the recommended readings are not usually adhered to. The screen owners/operators are allowed to do this because Piccadilly Circus is one of the few areas that are exempt from the usual lighting regulations. If you ever fly over London on a clear night you will see the Piccadilly Circus screens lighting up the skies.