In Part One of this blog, I described a common explanation for photosensor  failure – being mounted too high in a space.  When I ask why the sensor won’t work properly because it’s too high, the inevitable answer is “the inverse square law, of course!”  A look of smug satisfaction usually accompanies the recall of this tidbit from high school physics.  Case closed!  Everybody knows there is no defense against the infallible inverse square law of photosensor failure.  It’s as good as the Latvian Gambit in chess.  Or for you Trekkies, the Corbomite Maneuver.

Having taught Daylighting at the University of Colorado for many years, I’ve had the opportunity to ponder this control challenge.  And I don’t buy the ISL explanation for a nanosecond (as we’re talking about photons, a minute would be entirely inappropriate).  Here’s why.

It’s true that our most common light sources, whether the sun, an incandescent bulb, or a fluorescent lamp, emit light that weakens as the inverse square of the distance from the light source.  Twice as far from the light source, one fourth the light.  Three times as far, one ninth the light.  Pretty basic stuff.

Oops, that’s all for Part Two.  Continue on to Part Three for the conclusion.