[Teadaemon]

Ok, this will probably seem a little basic for some, but I've had a quick search through and not found quite the information I'm looking for (though several threads on here have got me to the point of asking this question).

Anyway, if it is correct to say that the only difference between a metal halide ballast and an HPS ballast of equivalent wattage is the presence of an igniter in the HPS ballast, is it safe to assume that what is described as a "70W Sodium floodlight", requiring an HPS bulb with an internal igniter, would have components compatible with the operation of 70W metal halide bulbs (not in the original housing, obviously)? The fitting I have in mind is available to order online from a major UK supplier of building materials for about the same price as a bare ballast from an electrical suppliers, and even includes an appropriate HPS bulb.

After spending far too many hours yesterday looking at various ballasts, capacitors, igniters online yesterday, my feeling is that it probably would be - most of the bare ballasts I've seen are listed as suitable for MH or HPS, which would fit in with what I've read elsewhere.

Also, I have another question on much the same subject - I've seen mention of 'HPS conversion bulbs' suitable for use with MH ballasts, are these in fact the HPS bulbs with internal igniters that I've seen advertised, as I've never come across one explicitly labelled as a 'conversion bulb'?

Actually it isnt correct to say the igniter is the only difference,the different ballasts have totally different operating voltages so they arent really as compatible as you may think

[R00KIE]

There are ppl out there who use they're hps ballast for mh by taking out the ignitor....
Probably not a horribly good idea but if I'm not mistaken it's relatively safe...
As for the conversion bulbs, I don't know if they make them to go from mh to hps but i do know they make them to go from hps to mh....

Yea people do it all the time here unless they're all FOS lol,Its probably not dangerous and probably not effecient because of the different voltages.

[Teadaemon]

Originally Posted by SKELETOR

Yea people do it all the time here unless they're all FOS lol,Its probably not dangerous and probably not effecient because of the different voltages.

As far as I've (just) read, differences in voltage only really apply when switching on the light - MH requires about 90V to form the arc, HPS about 180V, IIRC. After the arc is formed, potential difference between the two electrodes drops siginificantly, and as far as I'm aware is about the same in both MH and HPS lamps. If my understanding is correct, this is why HPS lamps require an igniter and most MH lamps don't.