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I am looking to use a motion detector to turn off lights with motion. Installing UV lights in a room for disinfection purposes and want those light to shut off when someone enters the room and the regular light turn on. I tried using a photo cell, but they take too long to turn the UV lights off.

This is a laundry room where the lights come on when someone enters the room. UV lights were added with a photocell to the room on a separate circuit. When the regular lights go off (no one in the room) the UV lights come on. When someone enters the room the regular lights come on and the UV lights do turn off, but after a few minutes, I need the UV lights to turn off as quickly as the other lights come on.

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    DPDT switches FTW Mar 10 at 19:52
  • Thanks Carl. But I need the lights to work automatically. Mar 10 at 20:47
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    AFAIK there are NO legal ways to use UV for residential use. UV disinfection for hospitals will lock out the entire room and all the windows are shielded for 24 hours, and it is combined with an aerosol disinfectant to cover areas where the light doesn't reach. If someone goes blind, you will be 100% liable and no insurance will cover you. Best to just hire a cleaner and spray the place down instead...
    – Nelson
    Mar 11 at 5:35
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    Yes, you would be quite wise to review this matter with your insurance company, or for that matter, your lawyer, and most definitely the property owner's lawyer. Your downside liability if this thing goes wrong could span all the way into the criminal courts. Mar 11 at 7:13
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    Thank you everyone for the input. After further review and consideration of your comments. We are NOT going ahead with the UV light installation. Mar 15 at 17:02
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Quite often motion detectors have a No and an NC connection so turning lights off can be achieved.

But I would consider using a relay and use that to switch between the two types of lights. The supply can then be controlled by a separate switch.

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  • Thanks Mike. This is a laundry room where the lights come on when someone enters the room. UV lights were added with a photocell to the room on a separate circuit. When the regular lights go off (no one in the room) the UV lights come on. When someone enters the room the regular lights come on and the UV lights do turn off, but after a few minutes, I need the UV lights to turn off as quickly as the other lights come on. Mar 10 at 20:42
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That sounds like a human safety issue, and those have very high operational standards. You need to think hard about the failure modes of this thing. It would be very prone to "fail-deadly" and that is not allowed.

What would be much better is to set policy that operators must manually turn the UV lights off, and help them in 3 ways (3-ways lol):

  • Have small visible violet lights come on whenever the invisible UV lights are on, so it is more apparent to humans that they are being irradiated.

  • make the room pitch black (other than the above) so artificial lighting is necessary to even be in the room and see. What will humans do? They will turn on the plain lights. Wire it so turning on the plain lights disables the UV. This is easy. Put the plain lighting on a 3-way switch, such that common is supply hot, traveler 1 goes to the human lights, and traveler 2 goes to the UV lights. Make sure "up" is human lights.

  • Power the motion sensor from the UV lights, but have it operate an annoying strobe or horn.

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  • Problem is you can't see UV lights. If someone leaves the door open and you look into it, you'll go blind. The failure mode for using UV is extremely severe and most likely very illegal, meaning no insurance will cover the damage.
    – Nelson
    Mar 11 at 5:39
  • Thank you everyone for the input. After further review and consideration of your comments. We are NOT going ahead with the UV light installation. Mar 15 at 17:03

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