I've got two light fittings which are basic pendant lights.

If I were to get them replaced with new fittings that have a battery backup ( kinda emergency light style that would turn the light on in the event of a power cut ), would they need any changes to the wiring?

  • "would they need any changes to the wiring" would they? what are they ? their wiring or the house wiring ? We do not know about the requirements for the lights you intend to use.
    – Alaska Man
    Apr 16, 2020 at 17:41
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    How will the light know the difference between a power outage and you just turning off the switch? If the power is off, how will it know you turned the switch on? I guess you'll need to find a working example of a light like you want to answer the questions you asked.
    – JPhi1618
    Apr 16, 2020 at 17:44
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    It really depends on the style of light and it’s controls . I have some emergency ballasts that have A sense wire if the sense wire sees voltage the light follows a the light switch if the Sense wire looses voltage the lights turn regardless of the light switch position my exit lights are set up so they are on all the time and if they loose power the battery backup kicks in so it depends on the type of system.
    – Ed Beal
    Apr 16, 2020 at 18:45
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    I very much doubt you can get a fixture for which the identical bulbs (or LEDs, or whatever) stay on in the case of power loss. It's just not cost-effective to add in the electronics for that sort of switchover. Get standard emergency lights, which simply switch on the battery power when the main power drops & releases a solenoid. (The main power never goes to the bulb) Apr 16, 2020 at 20:07
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    Aw shucks... you caught us! We're just giving you a hard time. Remember this well: You never need to explain your installation on an Internet forum because whenever you are working with tech, every installation of that tech is exactly like yours. Asking for 3-way switch wiring photos? Ha, we just ask for that to razz people. Main or subpanel? Just us trolling. We already know the answer to everyone's question. We're just making 'em sing for their supper! Apr 17, 2020 at 0:25

1 Answer 1


To answer the OP question is generally no, wiring changes are not needed for bulbs with battery back up. There are pros and cons to battery backup bulbs, so do your homework. Some people don't understand how they work and how to test them so give them bad reviews. You can't test them by turning off a breaker with no other loads on the same circuit turned on.

The lamp determines the difference between a power outage and simply being turned off measuring the resistance between the neutral and hot. If there is a low resistance between the hot and neutral, the power is off, the resistance measures thru other devices on the same circuit that are "on". If there are no other devices turned on in the same circuit, the bulb could be fooled and not illuminate. If there is very high resistance (or infinite), it assumes the switch is off. One other thing to look out for on these "battery backup" lamps, is they generally do not operate at full luminosity. They light up, but somewhere around 30%-50% or so of normal, to preserve battery life.

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    You might want to bring the contents of that comment down into the answer. While it's not a big issue on this stack, comments are designed to be short-lived and can be deleted anytime an admin wants to tidy up. Apr 17, 2020 at 0:28

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