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Lightbulb choosing circuit

Lightbulb choosing circuit

Lightbulb choosing circuit

I apologize in advance if this is not the place for this question. I have zero experience with circuits and don't even know what terms to search for.

I have a bug zapper that takes two bulbs and when the switch is turned on, both of the bulbs turn on. It is not necessary to have both on at the same time though, as one bulb is bright enough to attract flies and other winged nuisances. Those bulbs can be expensive so since one is good enough, I only use one at a time. It would be nice to have that second bulb as a backup though. That way there is no downtime when a bulb burns out.

Is there a simple circuit that exists that can do this:
  • If both bulbs work, power bulb 1
  • If bulb 1 is burned out, power bulb 2
  • If bulb 2 is burned out, power bulb 1
It would be a bonus if there was an indicator that showed whether bulb 2 was burned out or not, but that might be outside the realm of "simple" and anything outside of simple might get too expensive to be worth it, I'm not sure. Or maybe there is an even better alternative that I haven't thought of.

RE: Lightbulb choosing circuit

Put a dusk-to-dawn controller on the second bulb with the detector aimed at the first bulb.

RE: Lightbulb choosing circuit

Add a single-pole double-throw switch ahead of the bulbs that directs the power to either one bulb or the other. Simple, not too expensive.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Lightbulb choosing circuit

Can you just disconnect the second bulb? Cost is nothing if it works.

RE: Lightbulb choosing circuit

Power the 2nd lamp through an normally-closed contact of a relay, power the relay coil from a current switch sensing the 1st lamp. When the 1st lamp is running the current switch is closed, powering the relay and opening the NC contact. When the 1st lamp burns out the current switch opens, closing the NC contact and thusly turning on the 2nd lamp.

EDIT: I just realized if you could get a normally-closed current switch you could eliminate the relay. Not sure how common those are though.

RE: Lightbulb choosing circuit

I like this last one better than mine . . . the OP would have to mark the outside of the unit, though, to denote the bulbs as one and two since the condition


If bulb 2 is burned out, power bulb 1

would not be met.

Nevertheless, minor detail.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Lightbulb choosing circuit

Thanks for everyone's replies. I appreciate your time. I'll try the relay option and see how it goes.

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