Halogen track lighting dimming on its own?

I have a friend who recently bought some plug-in halogen track lights – Hampton Bay brand, from Home Depot – for her new townhouse. (The townhouse itself isn’t new; she began renting it a couple of months ago.) She tells me that when the lights are turned on, they’re at a ‘normal’ level of brightness for around twenty minutes or so and then begin to dim, ending up giving too little illumination to satisfactorily light the room. She says that if she then turns them off and turns the immediately back on, they’re still dim, but if she turns them off and waits a while, they end up fully bright again (at least for twenty minutes).

To her knowledge she doesn’t have an autodimmer installed in the lights. Does anyone have any thoughts about what, if anything, is wrong with her track lighting? Is there any additional information that it would be helpful to know?

I suspect the high current in the track connections to each light is causing expansion and increasing the contact resistance which decreases the current and thus a lower light output.Could there be more lamps connected on one track/circuit than is recommended?

Hmm. Thanks for your response. I asked her about this, and she said that the only lights connected to each track are the three it came with, and that she doesn’t have more than one track connected to a given outlet. She also says she has two tracks that appear not to have this problem. How would she go about testing whether your diagnostic is the cause?

It definitely sounds like a heating problem, good call Spingears.

Do all 3 lamps dim the same? If so, then the problem will be in a common conductor. Check for a hot spot near where the incoming power is connected. A poor connection could be heating up and causing this behavior. For safety’s sake, turn the light on until the lamps dim, then turn it off and look for hot spots. Be sure to check the plug and receptacle as well. The problem could easily be in one of them.

Also, I would swap the lights with another track. If the same lights dim, then we know it’s one of the lights. If the same track dims, then we know it’s the track. Once we know that, we can troubleshoot futher, but this will elimate a lot of what ifs.

With the additional information I would look at the plug/receptacle combination. When the lights/track heat up and dim, pull the plug and check the prongs to see if they are hot.
If so it is the receptacle with poor contact pressure.
Let us know results.

Thanks very much for the helpful answers and suggestions, spingears, Rhubarb, and Joey P. My friend’s out of town today, but I’ll relay this stuff when she gets back and report back with the results.

If anyone else has any additional thoughts until then, I’d love to hear them.

Metal wiring and track rails have more resistance when they get hotter*. You can’t do a lot about that, unless the fixture is designed without enough ventilation around the hot parts. In that case, you can drill holes to improve it.

If, as spingears said, the track-to-socket contacts get wonky with expansion, try this. Get a spray can of contact cleaner from Radio Snack, and clean the contact points. That is, spray the rail and slide the lamp back and forth after the fixture gets hot enough to go dim. You can also clean the tarnish off with an eraser.

A disclaimer! Disconnect the power before sticking tools or fingers in amongst the electrical stuff. You knew that, right?

Or it can be mounted on risers. Is that the right word? Something a half inch thick or so to bring if off the ceiling.

For a cheap Chinese product like this (ie one with an agressively minimal-cost design manufactured with lousy quality control), the best troubleshooting technique is to pull it down from teh ceiling, go back to Home Depot, and ask to exchange it for one that works right.

They sell thousands of the thigs which do not dim mysteriously. The OP’s friend has 2 that don’t dim mysteriously. Why keep a defective high voltage, high heat producing device in your home?

It would be nice to know if theproblem is in the product or in the house wiring. This may be a defective product or it may be exposing an unsafe condition in the receptacle. If the receptacle turns out to be OK, then yeah, take it back for a refund or a replacement.