I've got a RAB LOS800I/120 occupancy switch that has been installed in the basement for 17 months. It controls a CFL bulb in a ceiling fixture. Note that this switch is OK for fluorescents (has a neutral).
Until about 6 months ago, it was working fine, but after that, the time it takes to detect occupancy as someone comes down the stairs has increased, and become erratic.
I have determined that the problem is with the switch, and not with the light fixture or the wiring. I can always hear the switch close when it does, so I know when it has and has not been activated. I also know that the problem is not the switch contact, since the light always comes on when I hear the switch "click". Once the switch has closed, it remains closed until the time delay has expired with no occupancy.
When the switch was new, a person would have to be about halfway down the stairway before the switch would activate. Now, I frequently get all the way down the stairs before it turns on, and today, I went right past the switch and it did not turn on, but finally did after I had passed it.
I thought that maybe the color of clothing I am wearing affects the sensitivity, but after studying the specs on the switch, and observing it, I no longer believe this.
It is possible that humidity affects the sensitivity, but the operation does not seem to follow ambient humidity levels either, and there is a dehumidifier in a nearby part of the basement.
Could this be something as simple as the plastic window being dirty ?
Is there anything I can do with this switch other than replace it (ie; can I open it up without destroying it)?