Hi all, I have a question for you.

A co-worker was describing a situation to me the other day where a HID light (metal halide or high pressure sodium, I'm not sure) would light up for a while and then turn off; a while later this would repeat. I figure that this is thermal cycling, but I'm not sure where the heat-sensing element would be...in the ballast, or inside the lamp? He thought that it had something to do with the capacitor as he's heard of this problem being rectified in the past by replacing the cap.
There's a restaurant that we go to occasionally that, for the last 2 years or so, has had a pot light in their soffit that has been doing the same thing.

It would be nice to have a clear understanding of just what is happening because I'm sure I'll end up explaining this to a customer some day. I'd like to not put my foot in my proverbial mouth when that happens.

Thanks a bunch.

Shawn.

The primary cause of the bulb blinking is ... the bulb is dying. Only as a secondary cause is the ballast / igniter /capacitor assembly looked at.

If changing the bulb does not solve the problem, then the ballast assembly is to blame. Since the components are sold as a set, I'd change them all. There's no point in cherry-picking components.

Theory is fine .... but my experience seems to suggest that a bad ballast will often take a good bulb down with it. You almost never have just one part fail.

Thanks reno. So is the thermal overload mechanism inside the lamp?
This brings up another question I have wondered about: When troubleshooting lights that won't work, how can you tell which component is to blame? Let's say that a large building has a bunch of lights that don't work, do you replace just what needs replacing, or do you put in all new components?

Does anybody here use those testers that you screw into the socket, and if so are they worth the money?

Shawn.

It's not a thermal overload. Rather, the bulb can light only after a spark is 'ignited.' If the ignition circuit has a problem, and the arc is not maintained ... the bulb goes out.
Then, the ballast will attempt to strike a new arc. It succeeds, the bulb lights again.

Should either part - bulb or ballast - be marginal, the bulb will cycle on and off.


As for myself, I always start with a known good bulb. Then I follow up with an 'in use' inspection. If the problem returns, it's time to replace the entire ballast assembly.

IMO, there's really no safe, practical way to repair a ballast on the pole. At best, you look like a bumbling fool as you spend hours and make multiple trips to fix the problem. Remember- just because, say, the capacitor tests as "ok" at the time you replace the igniter ... the entire ordeal may have damaged it, and it may fail in a few days.

Contractor law says my work has a one year guarantee. I'm not going to be able to charge for those return trips!

Troubleshooting guide for HID fixtures
http://advancetransformer.com/uploads/resources/hid-troubleshooting-guide.pdf

Replace bulb, ballast and starter. Problem fixed.
I know the bulbs are expensive, so you may want to try the old bulb after replacing the above.

Is it possible that someone has put the wrong bulb in the lamp. I see it all the time.