> Given that there was no light present
> except that coming from the signal

There's plenty of light present. If there hadn't been, only the area in front of the signal would have been illuminated, right? Look behind the signal, you can still clearly see the snow and trees etc. Granted, the snow in front is brighter, due to the signal, but there's lot of light outside at night in the Seattle area, especially when it's cloudy.

We have so much light pollution it's pitiful. The night sky is so bright you can barely see the stars. When it's cloudy, it's often bright enough to read a newspaper. All that wasted light also uses lots of energy, so why aren't these "green" companies doing something about it?

Lots more info here: [www.darkskysociety.org]