4. OUTSIDE THE CONTROL

Up to this point we have talked about what is inside, or part of, the photocontrol. Now let us look at some of the external considerations.

4.1 Orientation

Conventional wisdom and ANSI state that controls should have the sensor facing north. This direction provides the most uniform light at the critical dawn and dusk times. If north is impractical due to obstructions, south facing is almost as good. Facing a control west will delay the turn-ON, possibly to the point of compromising safety, particularly if the control has an unfiltered silicon sensor. East facing gives earlier turn-ON and earlier turn-OFF. It is the same result as using an Inverse Ratio (see section 3.10) control facing north. This may be very desirable to improve visibility at dusk and to save burning hours at dawn. (If the control is installed south of the equator, best overall direction is south).

If you remember the first moonwalk in 1969, you may recall that a TV camera was destroyed when an astronaut briefly pointed it directly at the sun. A similar phenomenon occurred years ago with the early cadmium sulfide photocells. Prolonged exposure to direct sunlight deteriorated the cadmium sulfide layer and the plastic coatings. Hence, north was the only safe direction to face a photocontrol. Now, years later, the "north-facing" practice continues although it is technically out of date. The life of electronic controls is not reduced by non-north facing.