Starter circuit for HMI bulb

Thread Starter


Joined Jan 20, 2014
Hi ,
I have an Arri 1200/575 watt electronic ballast for an HMI lamp. I don’t have the lamp head itself and would like to install a HMI bulb into a film projector lamphouse using the ballast to control the lamp. I’ve tried looking for a circuit design for the lamp ignitor but can’t find any specific information on components. I have an ignitor that should be suitable but my question is does anyone know how I would go about hooking this all up together ? Presumably I would need some sort of timer that knocks the ignitor out once the lamp is established? I realise I may encounter flicker due to the mechanical nature of the projectors shutter although I am hoping the square wave from the ballast will render this unobtrusive. Any help or advice will be gratefully received. Best wishes, Jon


Joined Jan 23, 2018
Usually the starting function is either part of the ballast or part of the bulb assembly. The bulbs with starter electrodes that I have seen are all 2 terminal devices. The ballast somehow changes from voltage boosting to current limiting as the bulb heats up.


Joined Aug 7, 2020
You need a metal halide lamp ignitor
Mercury vapour lamps have starter electrodes, Metal Halide lamps don't, they don't have built-in ignitors, nor do they have ignitors built into the ballasts. They are ignited by a high-voltage pulse (4kV) which is superimposed on the mains suupply to the lamp after the ballast. They can only be ignited when cold, unless it is a hot-restrike lamp and a special hot-restrike ignitor which produces 20kV
There are two designs of ignitor, the type above has the step-up transformer, and is the most reliable.
There is another type which uses a 10V winding on the ballast to turn the ballast into a step-up transformer, but it presupposes that the ballast windings will withstand 4kV.

The ignitor is wired between the ballast and the lamp, of the three terminals one goes to the ballast, one goes to the lamp (the middle one with the better insulation) and the third one goes to neutral. It switches off automatically as soon as the lamp starts to draw current.

Make sure that you have the correct ballast for the lamp. It is the ballast that controls the power, not the lamp. Use a 250W ballast for a 400W lamp and you get 250W. Use a 1200W ballast on a 575W lamp and the lamp may well explode.

Thread Starter


Joined Jan 20, 2014
Make sure that you have the correct ballast for the lamp.
Thanks Ian , this is the ballast I have

Unfortunately I don’t have the cable , so I guess I just need to get a cable and work out which three wires to connect ? When you say one term of the ignitor goes to Neutral is that back to the ballast via one of the pins or just the main neutral that is in the lamphouse (it has a 230 v supply to power cooling fans and a psu that triggers a relay ) thanks , Jon