as per object, is it possible??
what wuold happen?

thanks to you all

In post 7 I think AZ gives a good guessimate of what happens %wise

http://www.lumenlab.com/forums/index.php?showtopic=20156

thanks, i just realized that using a ballast powerful than the lamp is overdriving (of course) instead of under driving as i thought.
i don't want to overdrive my bulb....

there' isn't a trick which can allow me to use a 250w bulb with a 400w eballast for a while.
this could be just to solve a temporarly issue with my original ballast

You might be able to use the cap from the 250w instead of the 400w s cap ,,, But if I were you I would pm arizona video and ask him, he may be able to advise or recommend something. Remember any mods done by you or advise given, it is still your responcibilty to practice safety.

The lamp might run at around a 370 watt power level but we have not tried a Eballast and a 250 so we don't know for sure.

It may be that the Eballast is smart and will run the lamp 400 watts which is a lot,perhaps too much, for a 250 watt lamp.

If anything the lamp will need lots of direct cooling from a fan and there is a good chance it might fail.

If you want your lamp to last thousands of hours I would not do this. If you don't care that much if your 250 pops then let us know how it works out.

It would be nice to look inside a Eballast one day and reset the power level to 300 or 325 watts or so for overdriving the 250 watt HQI lamps but no one has taken the time and it will be a little tricky.

I have more than a few years if electronic training but a Eballast is a complected device to mess with.

It's been a while, I was away for quite a long time, but just to let you know: this setup works, I've been using it for many months, I think few hundreds hours on the bulb, and there are no problems yet. It's an Osram E40 250W bulb, with a 400W coil ballast.

Yesterday I replaced this bulb with a 400W one, just because I found a 6100K bulb, the picture is noticeably dimmer, but colours are nicer, so for now I will leave it like this and stop testing owerpowering the 250W, it goes to the drawer now.

Further to this: the benefit of more lumens from an overpowered lamp is not that obvious, as the colour temperature is significantly lower. So the image is yellowish, and to correct this you need to adjust RGB settings, greatly reducing R channel, and significantly G channel, so finally you don't get that more brighter image as the lamp gives more lumens. But still there is an improvement, the lamp is cheap, and in my case it's proven to work for a long time, so it's worth to try.