Q:

Lighting metal halide lamp

I want to use some metal halide lamps (5-7*150W) to get some decent lighting in my room.
Unfortunately, inductors for these lamps have weight about 2kg each. I cannot accept 10kg of metal hanging near the ceiling :-) So I must go with electronic ballast, but their cost is about 100 bucks per lamp. Forking out 500 bucks does not sounds good.
So, I am thinking about making 5-channel electronic ballast for these lamps. While basic idea looks simple (just make constant current supply), the main problem is ignition.
Is it possible to avoid HV ignition by feeding RF signal into lamp, so that discharge would start just like in induction lamps, and after some time turn on the current?
And finally, do I still need alternating current direction in the lamp? If yes, how fast it should change?

A:

Microchip has a dsPIC app note on electronic ballasts for automotive (not so different from what you have). They use an HV igniter to get the lamp fired. You will also see that AC is used once the lamp is fired. 
A little research showed me that induction lamps don't have electrodes, and need HF applied constantly to excite mercury amalgam into emitting UV, whereas a metal halide lamp relies on an arc to be the UV source, and doesn't appear to have a mercury amalgam pellet at all.
It appears that the induction lamp is specially constructed so that the external electromagnet is close to the amalgam pellet. If there is no pellet in the HID lamp, game over. Even if there were, I don't know if you'd be able to excite it given the dimensions of the glass around it.

A:

Don's Lighting Page has a lot of information on lamps from a DIY perspective.  If there isn't a driver circuit listed in this site, you probably can't do it as a hobby.

