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.