# What keyword(s) to search for a switch to turn OFF a circuit at dark? **URL:** \ **Category:** Factual Questions\ **Created:** [July 10, 2009, 8:27pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603 "2009-07-10T20:27:33Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![janeslogin](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@janeslogin](https://boards.straightdope.com/u/janeslogin)\ **Post date:** [July 10, 2009, 8:27pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/1 "2009-07-10T20:27:33Z")
Spouse wants to turn off a 12volt 2amp circuit at or near darkness and turn it back on the next day. We’re having trouble finding this. Seems simple. Must be a keyword search problem. Suggestions? ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [July 10, 2009, 9:05pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/2 "2009-07-10T21:05:24Z")
What is a photoelectric switch, Alex? ---
**Author:** ![emmaliminal](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@emmaliminal](https://boards.straightdope.com/u/emmaliminal)\ **Post date:** [July 10, 2009, 9:11pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/3 "2009-07-10T21:11:38Z")
> [@Nametag](#): > > What is a photoelectric switch, Alex? Not the OP’s Q. What do you call a photoelectric switch that does exactly the opposite of what most people want it to do? ---
**Author:** ![janeslogin](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@janeslogin](https://boards.straightdope.com/u/janeslogin)\ **Post date:** [July 10, 2009, 9:30pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/4 "2009-07-10T21:30:39Z")
> [@emmaliminal](#): > > What do you call a photoelectric switch that does exactly the opposite of what most people want it to do? Exactly! ---
**Author:** ![ivn1188](https://avatars.discourse-cdn.com/v4/letter/i/e480ec/32.png) [@ivn1188](https://boards.straightdope.com/u/ivn1188)\ **Post date:** [July 10, 2009, 9:40pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/5 "2009-07-10T21:40:22Z")
The keywords you want are “normally open”. [Like this one.](http://www.made-in-china.com/showroom/yncync/product-detaillbIxUzAcYLVF/China-Photoelectric-Switch-G30-3C101NA-.html) ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [July 10, 2009, 9:40pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/6 "2009-07-10T21:40:26Z")
But you can use a turn-on photoelectric switch in the same situation. Just have it turn on the circuit that turns off whatever you are controlling! ---
**Author:** ![adhay](https://avatars.discourse-cdn.com/v4/letter/a/ecd19e/32.png) [@adhay](https://boards.straightdope.com/u/adhay)\ **Post date:** [July 11, 2009, 1:49am UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/7 "2009-07-11T01:49:57Z")
This maybe? [http://www.amazon.com/Coleman-Cable-04600-88-Digital-Outdoor/dp/B00004SQHX](http://www.amazon.com/Coleman-Cable-04600-88-Digital-Outdoor/dp/B00004SQHX) ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [July 11, 2009, 6:38am UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/8 "2009-07-11T06:38:23Z")
Large spaces like auditoriums are frequently wired so that the switches only control a small current, which triggers a _contactor_ (an electro-mechanical relay) that controls the much larger circuit for banks of lights. And industrial installations use them for large motors. So get such a contactor, and wire it such that a standard photoelectric cell turns on the power that triggers the contactor to switch _off_. Any local electrical supply outlet should have an appropriate contactor available. ---
**Author:** ![janeslogin](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@janeslogin](https://boards.straightdope.com/u/janeslogin)\ **Post date:** [July 11, 2009, 5:59pm UTC](https://boards.straightdope.com/t/what-keyword-s-to-search-for-a-switch-to-turn-off-a-circuit-at-dark/502603/9 "2009-07-11T17:59:02Z")
(ivn1188s link may have something useful and we are investigating.) Useful specification I failed to mention; it is 12volt 2 amp DC circuit that must be turned off at near dusk and back on at near dawn. It is located out in the desert so whatever operates the switch such as a timer must be either solar or battery operated.