.....On a side note, towards the subject, kinda..... We use little square photo cell's, can't remember the name, on lighting control circuits for a lot of our pole lights. They only last about a year, sometimes less.
Know of a good brand or stile that would last longer?
I call 'em Ice Cubes. Not to be confused with ice cube relays.
As for longevity problems, are you controlling the lights directly with the PCs, or using it to drive a contactor?