Identifying cause of light flickering?

Question

I've got 2 lights in the house that have an intermittent flicker (we can go for days without having it at all, then it'll happen for a bit). I've not seen them do it at the same time. They are on the same circuit (but different switches). It's not much of a flicker really, closer to a very subtle change in light output, just enough to annoy and concern me (my wife didn't even notice until I pointed it out). They are 2 of the highest power consumers in the house, one being 200 watts, the other 180 watts. For comparison, our third highest consumer is 160 watts, is on a different circuit and has never been seen to flicker.

There is also a 60 watt bulb on the same circuit as my flickering lights and on the same switch as the 200 watt fixture. This one never has been observed to flicker (but perhaps I simply can't notice it as the light output is so much lower).

I'm at a loss as to how to narrow this down further. I've observed other light and appliance usage in the house and it doesn't seem to match up with anything. The closest I've gotten to a pattern is that the 200w unit seems most likely to flicker when used between 5-6am and the 180w when used between 8-9pm. I'm not opposed to calling an electrician, but since I can't reproduce it at will, that seems like I'd probably end up throwing a lot of money at it for no results.

edit

I've now been able to isolate as the other light on the circuit has started flickering (very faintly) now. It's only when the lights are on due to both (3-way) switches being "down". If they're both "up", the lights are flicker free. I'll be checking the connections at the switches now. If not the connections, is that failure usually a bad switch or a bad connection wire for the 3-way setup?

Answer 1

It was a bad switch.

The isolating it to when both switches were in the same position was as far as we could get for diagnostics. All connections were inspected and seemed fine. I finally gave in and just bought 2 new switches. Upon trying to install them I noticed mismatches in wiring colors so I brought in an electrician who was able to sort things out (and tagged the wiring for me). He then removed the oldest looking of the 2 switches and replaced it with one of my new switches. The flickering problem is gone and I have a spare switch now...

Answer 2

For old fixtures with a screw-in lamp base, I think the cause of flickering is often that the center hot contact is not making firm contact with the bulb. I pry the center contact up slightly with a screwdriver or a crochet hook. I also scrub oxide off the contact with a pencil eraser, but I'm not sure that does anything. Naturally be sure the switch is off and check the socket with a non contact or contact voltage tester before inserting anything in the socket.

Answer 3

I will tell you what I found with some flickering lights.

I had two light bulbs flickering on the same circuit. I inserted a voltmeter into one of the sockets (removed the bulb), and when the other light would flicker, I would see the voltage drop momentarily in the socket I was looking at. Which in my mind would indicate it's not the bulb (the fact that I had two bulbs do it at the same time is also a good sign there, heh).

Next step is to isolate the problem. You can either start "close" or "far"

If you're starting close, go to the switch, pull it out from the wall, put your voltmeter lead on the incoming power, and one on "common" or "ground" it should read 120. When the lights flicker does it change? If not then the problem is somewhere between the incoming lines and those bulbs (hint: might be the switch itself, or maybe where it connects to one of the fixtures). You could also try putting your voltmeter leads on the wires leading out of the switch, do they drop?

If voltage is still dropping there, go to the power box, identify the breaker it's on, and put one voltmeter lead on the breaker output, one on common. Does the voltage drop? You can also try the same thing with the main large incoming line (though that's pretty scary, might want to have a pro or a friend help). Does the voltage drop? If it's still dropping from the main coming in, time to call the power company and ask if they can look into it (in my neck of the woods they can install some kind of "meter" to monitor it for you temporarily).

In my case I tested the "main" and it didn't drop in voltage. I was then about to test the breaker when I noticed "that's odd, one of those breaker looks like it's sticking out slightly more than the rest" and sure enough, it was the one feeding my "periodically flickering" lights, so plugging it in more firmly I believe solved it for me.

If it's LED's (especially on a dimmer) then there are other things that could be at play, but still worthwhile to check if voltage is a problem.

Answer 4

the best way to understand any of this is are the fixture from China and the bulb from USA? I notice that all bulbs have a different degree of width, if you use the tightest fitting ones, you leave the bulb socket loose for the smaller ones, you can replace the ceramic lamp socket or put a tiny amount of tin foil around the loose bulb so the contact is snug, do this with the switch off, and only wrap the outside with the threads, not the bottom contact, I've don't this, on many china ceiling fans, if it mine the foil trick is a fix, if it's for a customer, I just replace the socket and charge the player $$$ IT'S UP TO YOU, now as far as these advice thread, it's been almost 100 percent with bad info, as a handyman I always run across a crazy scenario, and I've found that most people posting insight are full of it, if you need help just find my facebook, chances are I've fixed just about everything in the last 40 years