Hi, I rewired and cleaned up a brilliant old Thorn HIPAK 400w mercury vapour fixture. When switched on, the lamp glows a very faint pink-orange colour. I'm assuming that this can be fixed by simply replacing the lamp, and is not a problem with the ballast.

Do you have any experience with discharge lamps?

Almost all of them need time to warm up. Depending on size and type, that time can range from 1 to 10 minutes.

Your picture looks like a completely cold MV lamp. The color you see is the color of the phosphor coating, plus a tiny bit of blue light from the still cold arc tube. As arc tube pressure rises, the light becomes whiter (no pink hue anymore) and much brighter.

It was like this for at least 3 minutes, gradually getting slightly dimmer. I just switched it on again, and now the lamp will not glow at all. My plug in meter reads 1.5 amps, 0.0 power factor.

Luminaire test :
Measure the resistance between the input terminals (plug pins) and socket contacts :
 - One should measure a small resistance up to few Ohms. (Normally L to center contact in the socket)
 - One should measure a direct connection. (Normally N to outer contact in the socket)

If any of this does not measure right, then you have a bad connection in the wiring or an internal bad connection in the ballast

Use an E40 to E27 or B22 adapter, or connect an ordinary E27 or B22 socket in the luminaire (instead of the E40), and try to power it up with an ordinary Incandescent lamp (anything like 40..60W) instead of the Mercury lamp. It should light up at near normal brightness



Lamp test :
Connect the Mercury lamp outside of the luminaire, in series with either an Incandescent lamp of medium power (anything like 40..60W 230V) or Fluorescent choke ballast (pretty much any 230V) to 230V

See if the lamp strikes. It won't warm up much with such ballasting and may remain flickery, but it should strike and remain lit without extinguishing

Don't run the lamp for too long this way as it does wear out. (The mercury lamp is supposed to get quickly to its high power state, not stay in the starting state for long)

I got a replacement merc lamp today. The fixture is now fully working. Thanks for your help!

Nice! More 400W fixtures! I have two thorn MBI-400's I need to finish up one day. They both have dead igniters. I have replacements. Just haven't had the time to fix them yet. I have a new old stock reflector so I'll be able to make one of them pristine, the other will... Look a bit meh. But they will both work! Massive power users, but they're extremely cool and no amount of other lamp technology comes close to how impressive I think these big things are! I have a few spare lamps but not a huge amount. They last a decent number of hours, but they're driven really hard!