Discharge floodlights - how to tell which component has failed ?

[Nick]

I have several of these. 70/150/250/400 watts. All operated by dusk/dawn sensors. Mostly metal halide but still a couple of son-t (I think) which will be replaced as they fail, if not before. Variety of lamp types and fixtures. Some have ignitors, some don't.

Is there any (easy) way to tell which component has failed when a light stops working?

Thanks,

Nick.

[Andrew Gabriel]

Normally the lamp itself. The other components tend to be much more reliable. Have you had any known cases of other components failing?

All the lamp types you list need an ignitor, although some of the lower powered versions are optionally available with integral fluorescent tube style starter inside the lamp, and in the case of electronic ballasts, it will be integral with the ballast. Otherwise it's a separate long-life module connected to the ballast which you don't normally need to replace.

SON lamps fail either when the emissivity material is all worn off the electrodes (just won't light or quickly extinguishes after doing so), or when the arc tube gets too stained, causing the tube to overheat, give off bright white colour, extinguish, and restart after cooling for a minute, cycling like this continuously. A problem I hear from US colleagues is that this SON cycling can burn out the ballast, but I've never heard of that happening over here, so I suspect that's just a reflection of the quality of the parts they use and thermal tolerances they [don't] build in.

Metal halide change colour markedly as they age (unless you buy much more expensive ones which counter this effect) and get dim, but may carry on running, or can explode in rare cases. The luminares are designed to contain hot lamp fragments for just this situation.

[Nick]

Thanks Andrew for an informed, and informative, reply. Yes, I have had component failures before and am suffering such now. My first move is always to check that the luminaire is receiving power from the dusk/dawn sensor. Next, check the lamp by swapping into a known working luminaire, unless the lamp is obviously u/s. That is about the extent of my knowledge, hence my post asking how to tell which component has failed. In the past I have replaced either entire luminaires or all the working components (ballast/ignitor/capacitor[s]).

Current problem is a 400W LeGrand metal halide floodlight. Power supply tests good and the ballast is humming. The lamp works in another luminaire. Both the lamp and the ballast are looking somewhat aged. The lamp holder is also good. No charring or burny marks to the ballast and no sign or smell of magic smoke release. So I reckon it is probably the external ignitor and/or one/both of the capacitors, although these show no obvious sign of failure. This afternoon have swapped the gear tray from a new luminaire and it now burns bright. Old gear tray on the bench awaiting parts. Perhaps I would be better replacing all components. I would still much like to know how to test the ballast, ignitor and capacitors.

Many thanks, and best wishes for a very happy Christmas.

Nick.