Hi all,

I bought a NOS general electric 50W HPS canopy fixture from e-bay. I plugged the fixture in tonight to check it out and film the start-up, but after 3 or 4 minutes the bulb turned off. It also appeared to be experiencing issues striking. I turned off the power to the fixture, let it cool down, and tried again with it plugged into the kill-a-watt meter. The fixture started up pulling ~2.5amps and wattage climbed as amps fell, until around 60 watts when the bulb turned off. I left it powered to observe what would happen and the bulb re-struck after maybe a minute or so.

This seems to be typical end-of-life behavior for a HPS bulb, but as it is NOS (and I would like to give the e-bay seller the benefit of the doubt), this does not make sense. I posted pictures of the bulb, transformer, and fixture. Does the bulb or ballast have some manufacturing defect that I am missing, or did I get punked by an e-bay seller?

Please give me your thoughts, as I am new to the hobby of collecting and using HID lighting, but I am eager to learn.

Cycling on/off is the usual EOL behavior of HPS lamps. But your lamp have only one end of the arctube blackened.

What else do you think could cause the cycling?

Or do you think it is just a bad bulb?

Do you remember if your lamp had this blackened end of the arctube right out of the box, before you tried is?

What is the line current after some run-up, just before the lamp goes out?

There may be just something wrong with the lamp, or the ballast may be defective, partial short causing too much current to be drawn.

Unfortunately I do not recall if the arc tube was blackened, but I think it may have been. I do know that when I initially started the fixture, it took around 35-40 seconds for the bulb to finally strike and begin glowing yellow as HPS does.

I conducted two tests earlier today tracking the wattage on my kill-a-watt meter and tracking the line current with a fieldpiece SC260 around the hot wire.

The lamp started up and attempted two strikes before lighting after about 15 seconds. The lamp drew about 2 amps during each strike attempt (there were two) and then drew 1.67 amps and ~41 watts.

The lamp then pulled the following amps at each watt reading:
45 watts - 1.61 amps
50 watts - 1.53 amps
54 watts - 1.45 amps
56 watts - 1.41 amps
58 watts - 1.35 amps
60 watts - 1.21 amps
61 watts - 1.27 amps
61.5 watts - 1.19 amps
61.5 watts - 1.14 amps
60 watts - 1.04 amps
59.5 watts - 1.01 amps
45 watts - 0.99 amps

Then, the lamp turned off. The sequence above lasted about 2 minutes and 45 seconds.

I decided to keep the lamp turned on to see what would happen on the restrike, and the lamp ran for about 20 minutes.

It began pulling 60 watts and 1.51 amps, and and after a minute or so things evened out and the lamp was pulling between 59-63 watts and the amperage fluctuated between 0.98-1.05.

So it seems like the issue is cold starts. Any thoughts?

I will try to upload more pictures of the bulb and tonight if I have time I will make a set up that I can video which will show the watts, amps, and the light all in the frame of a video that I will post to youtube and share here.

Nominal lamp current for S68 lamp is 1.18A so the ballast is definitely not overdriving it. So I bet the lamp is just defective. American low voltage HPS lamps run on a low open circuit voltage, so can be rather fussy to sustain the discharge.

Even when looking at the total power (about 60W in its maximum), it corresponds to what I would expect on a 5W ballast. So definitely a bad lamp (could be worn out, damaged, defective from the factory,...).