The Logic Behind Shielded Light Sources

In most cases we automatically shield a light source from view so that we may see the foreground clearly. We dim our car headlights for approaching vehicles. We wear hats or sunglasses in the sun. We use lamp shades on desk lamps. In the year 2014, NASA plans to launch a space based observatory called the Terrestrial Planet Finder, which will search for small planets by blocking the light of the parent sun. Why then, do we not automatically shield outdoor security lights?