...But does it work with The Clapper?

Digital billboards deliver advertisements using thousands of tiny lights which must burn at different intensities throughout the course of a day. In broad daylight, the lights are cranked up to about 95% of their capacity, and at night they are dimmed down to about 5% so as not to distract drivers.

Some billboard companies control the brightness of their displays using time tables- specific intensities are assigned to specific times of day. What this doesn't take into account is that the orbit of the earth causes sunrise and sunset to happen at different times throughout the year. Not to mention factors such as cloud cover, rainstorms, etc. Furthermore, highway safety laws require that signage should not increase the level of ambient light in an area by more than a few footcandles.

To ensure that these laws are strictly adhered to, and that advertisers messages are clearly visible at all times of day, Clear Channel Outdoor has invested in dimming probes for each of their digital billboards. Seen below, these sensors are mounted to the top of the display, and measure the changing level of ambient light. The PC inside the board then adjusts the brightness accordingly. Though these devices aren't cheap, they are well worth the investment to make sure advertisers are getting what they pay for.