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I need a way to detect if the lights go off ? Answered

To make it simple I have a sealed box in the box are 2 screw-in fluorescent light bulbs 25-26 watts each ..I need to have a way to detect if one or both of the lights go off !?

The lights are used to keep my plants worm in the winter. the boxes are sealed for the most part but if one of the lights go out the temp will drop and my plants will die! So I thought if I could some how add back-up lights that would come on.. if one or both lights went out.
Sorry question sounds good in my head but don't know if Am asking the question right. thank you!!


How about cutting a small panel out of the box and covering it with glass or plexiglass? That way you can see if the lights have gone out; and the small panel shouldn't have any major effect on the temperature inside the box. You can also keep an eye on your plants that way.

On a side note, I would also be concerned if the box is completely sealed, as plants (as do all living things) require oxygen to live...

Sorry didn't give all of the info I do have a small viewing area in the box

As for the plants I have been doing this for years the plants go dormant in the winter so there is no problems.. just have to make sure they don't freezes :)

What I need is for some back lights to come on if the other lights go out!

What would work well is a thermostatically controlled outlet. Plug your backup light (or heater) into the outlet, and put the thermostat into the greenhouse box. When the temperature reaches a certain level (meaning your main lights went out), the backup will then turn on.

Here's a link to a variety of options. It just depends on what you think you need (temperature wise) and how much you want to spend. If you search "thermostatically controlled outlets" you should find other options at Amazon.com and from other websites. A similar DIY method can be achieved with the thermostat on a baseboard heater.

Hum very interesting site thank you.

You know I started thinking after looking at of the ansers why not just add two more screw-in light bulbs each one having a light socket with Photo Control...you know the ones that Automatically turns lights On at dusk, Off at dawn. Then add a small tube that covers the photocell to help direct the light from each bulb. The tube will dect that one light has gone out and then it will turn on only one of the bulbs...hum this might work what do you think!!

That should work also. Just direct the tube onto your main lights, and if they go out, then the backups should think its night and come on automatically. You just have to make sure that no daylight can reach the sensor (in case the bulbs go out during the day).

You're welcome.

BTW, whenever you've got the answer you need, you can mark your question as "answered" by clicking on one of the blue buttons (but there's no rush). ;-)

Strap or glue an LDR to the bulb and measure it's resistance - you will see the change when the bulb goes out.


This may a good idea for another idea I have thanks!

Do you need the light., or just the heat ?

Heat can be made failure free with some resistors - they'll last indefinitely.

If you buy some 4 power resistors like these:


And wire them in series, you will have close to 50 Watts of heating, which can't burn out.


either. If you have mains, you can run them directly on mains, if you have high voltage DC, it doesn't change, if you have low voltage DC, come back and tell me what voltage.

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6 years ago

It sounds like the issue is temperature and not if the lights are on. A simple solution for that would be to get a remote temperature sensor. They have wireless ones that can transmit for a pretty good distance and they are not expensive anymore.

I do have a remote temperature sensor sorry should have put that in question.
What I need is for some back up lights to come on if the other lights go out!
just in case I am not at home are when sleeping.