2018-05-26

K4221C Photo Cell Adjustment

I just replaced a K4221 Photocell with a new one.

The old photo cell failed in the "on" position, which is actually a great failure mode - I use the photocell to control indoor and outdoor lighting, and for safety reasons its important that it works.  So the lights being stuck "on" is a decent failure mode.

But the photocell was stuck on for, um, many years.  I didn't really notice that there was a photocell, and was just accepting that the lights were on 24x365.

Now with the photocell, my lights will be on roughly 16 hours a day. That saves a third off of my lighting bill.  In the scheme of things it will only save me a couple hundred bucks, but hey, rather I get it than OPEC.

My photocell has a tough job.  It is to turn on necessary indoor and outdoor lighting when it starts to get dark outside.  But the challenge is that the photocell is positioned so it receives a lot of artificial light from the urban street, and it is unreasonably complex for me to move it.

My goal is to get it to trigger the lights acceptably, and that means have it be "on" when it needs to be "on".

In the worst case, I can just disable it.  I can just leave the lights on 24x365 and be done with it.  And that might be the solution I go with.  But for now, I'll fiddle with it.

I oriented the sensor so it faces away from direct lights, in hope that will help.  I also used the metal shutter and some handy electrical tape in order to shield the sensor as much as possible.

The fortunate part of it all is that I can adjust the sensor from the ground.  There is no need for me to climb ladders or other nonsense.

I figure it will take a few weeks to get it just right.

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