Photo cell going bad?

[galighting]

I have a customer that states her landscape lighting comes on and off during the day. I've checked for anything that may be "faking" the photo cell and found nothing. This trany has a PC/timer combination. Think I should replace the PC and go from there?

Thanks, BD

[sitelights]

The simple answer is: replace the p/c but you may want to read below for some possible causes of the anomaly you describe. Also, the site search engine can be queried by using a keyword or keywords (they must be at least 4 characters long) such as "dusk", "dawn", "photocontrol"; and so on which will take you to numerous posts on this topic.


A photocell/timer combination addresses the problem of correcting the ON-at-dusk variables; the system is turned ON by energizing the the p/c prior to dusk, allowing actual dusk (which varies + or - about 2 minutes a day) to trigger the p/c to switch the transformer ON each evening.

In my latitude I set the timing device to turn the p/c ON at 3 PM which is about an hour before actual dusk occurs on the shortest day of the year. Thus dusk is "sensed" rather than timed.

Since p/c operation requires some time after it is energized (the instructions state "up to five minutes" depending on make/model) to switch it is possible for the system to turn ON briefly at, in my example, 3 PM or any day after 3 PM during dark periods caused by stormy, cloudy weather. The lights will switch OFF as the dark day again becomes bright.

Since the lights will go OFF when the sky becomes bright enough to trigger the p/c it may be that your client is noticing this "glitch".

Apparently you have checked for improper aim of the p/c (which should "see" the northern sky) or the possibilty of the p/c being shadowed by shrubs, etc. so the problem is either "phantom" ON (dark sky during the day) or a failed p/c.

Depending on the brand, some fail OFF and some fail ON. In the failed ON mode the lights revert to timer-only setting; failed OFF results in no lights at any time. Most common brands "drift" after about 5-8 years or sooner and are slow (and slower) to switch.