I have a persistent problem with the upstairs ceiling lights in my house where they often run dim for a while and then return to full brightness a few seconds later (at most 1 minute). Sometimes turning on a light will cause another that is already on to dim as well.

Could this problem be attributed to faulty light bulbs (some of them are energy saving bulbs)? Or perhaps a loose connection in just one of the light fittings? I want to see if there's any troubleshooting I can do before calling someone out.

  • Are the energy saving bulbs LED?
    – mbeckish
    Commented Mar 11, 2015 at 13:41
  • Is there something with a heavy motor on the same circuit, such as an air conditioner or a refrigerator?
    – bib
    Commented Mar 11, 2015 at 13:56
  • @mbeckish - Upstairs I have one CFL and two Halogen, from memory. Got a few GU10 bulbs in the kitchen which are LED I think, which sometimes take a couple of secs to turn on at all
    – james246
    Commented Mar 11, 2015 at 14:23
  • @bib - There's an extractor fan in the bathroom, but the problem occurs even when that is off. I have no AC, and a small fridge in the kitchen
    – james246
    Commented Mar 11, 2015 at 14:24
  • 1
    @bib - The lights are only dim when they are turned on, they brighten up shortly after so unless the fridge is permanently hogging power (rather than in brief cycles) then I'm not sure if that'd be the issue? I'm mostly concerned that the wiring of the lighting is faulty in some way, but I don't know how to identify that without a professional. Would be nice if it was just a bad bulb, but I don't know if that's possible (one bulb messing up a whole circuit)
    – james246
    Commented Mar 11, 2015 at 15:12

2 Answers 2


I'd recommend starting by replacing the bulbs to rule out any issues with them.

Assuming the bulbs has been ruled out, it sounds like a bad electrical connection. If it is affecting many lights, then it's likely upstream, perhaps at the switch, but if not, in another connection point. Could even be in a receptacle along the same circuit.

Do you know if your house uses aluminum wiring? If so, you should contact a qualified electrician since AL wiring requires some expertise, and the dimming lights are a good sign that there is arcing occurring which can be a fire hazard (it could be a fire hazard with copper too, but much more common with aluminum).

If your house is wired with copper, you can start by first turning off the power at the breaker, and then inspecting all of the connections at each light fixture and the switch. Look for lose or corroded connections. You're going to need to work backwards from the fixture to the panel, until you find a cause.

Based on the info you provided, it could be a lose connection with either the hot or neutral wire. If you observe the bulbs getting brighter than normal, that is usually a sign of a open/lose neutral wire.

Lose connections usually cause arcing, which can cause a fire, so this is not something I'd leave indefinitely. If troubleshooting this is outside of your skillset, it's always best to contact a licensed electrician.

  • Thanks, I'll try a new set of bulbs in each light and see if that helpers. Will go check the connections at the weekend if that doesn't help
    – james246
    Commented Mar 11, 2015 at 16:00

Many CFLs take time to warm up, covered ones are worse than the naked spirals. See http://www.litetronics.com/lighting-technology/why-do-covered-cfls-have-a-long-warm-up-time.html

  • Thanks for the link. The CFL bulb barely lights up and worked OK in a lamp last time I checked. Will replace with a non energy saver to test though
    – james246
    Commented Mar 11, 2015 at 16:00
  • Based on OP's description I believe this is the correct answer. Commented Mar 11, 2015 at 18:26

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