Incoming "stupid question" LOL. If I bought a 400watt MH ballast but only wanted to rig it with a 250w bulb, would that work? I know it can be done with "normal" bulbs, I just want to make sure :)

I wouldn't do it. There's a technical reason I've read why not to, but yeah. I wouldn't.

Certain ballasts are designed to be used to handle either bulbs, but I'm not sure what ones. If you do some more research you could probably find it. It's just like Ice Cap's ballasts, they can tell what configuration of lengths of bulbs you're running and they adjust the outgoing wattage to handle that load. Don't try it on anything other than a ballast that specifically says it does so though.

I was actually just thinking about this today and was going to post the same question. So are you saying some Ice Cap ballasts can handle this and can be done or still not recommended?

Ok, well, I have another "stupid" question now Say I put a 250 on one side of the tank and a 400 on the other. Will that look visually bad/different (looking at the tank will one side look much brighter)? I plan to do that and then add some t5s to add some color, but I don't want it to look stupid. I figure if it looks alright I can put some of the more light demanding stuff on the 400w side.

the visual aspect of the two bulbs wont look very good at all, as far as running a 250 on a 400w ballast havne't seen any that do that, have seen 150/175 ballast that will do either or but not 250 and 400, thats a pretty big step in current, you would be over driving those 250s and prolly blow them in a few days would be my guess on that :) but.............if you want to try it out and make an experiment on us and let us know how it works i'm all game for it and would love to come and help :)

Posted By Gered on 09/14/2009 03:07 PM
  So are you saying some Ice Cap ballasts can handle this and can be done or still not recommended?

The more I look into it the more I think it's not possible on metal halides. I know it works just fine with T5's and VHO's. I know with positivity that the Ice Cap 660 T5 ballast can run as little as 2 bulbs or as many as 4 bulbs, so it's obviously a drastic change in wattage. I had a VHO ballast that ran 4 bulbs for a while, then I changed my setup when I get the Ice Cap 660 ballast and now that same VHO ballast is only running two bulbs now. The descriptions on some of the metal halide ballasts suggest that they can do this with halides, but I'd need to call a sales rep and talk to them about it before putting any money into it.

Also, I think I remember seeing pictures of someones tank that had two different kinds of lighting. I think it looks goofy, but it might be something that appeals to certain people. Try a google search or something...

Good luck.

I think you can get away with it if, for instance, you have three bulbs over a six foot tank and have the different one in the middle.
Example: 250 - 400 - 250
I would imagine there will be a big difference between the 250 and the 400 so it will be very noticable to have just two in a tank.

also i would think if the k values are different there would be more of a color difference between the two...like if the 400 was a 14 k and the 250 a 20 k the 250 is going to be clearly more blue but if they are both 20 k's could you tell a difference brightness wise?? with the t 5's right now i have three ballasts running 6 bulbs 2 each...one is running the actinics, one the white lights, and the third is running one of each bulb, all the bulbs are 39 watts but only one of the ballasts is 39 watt, the other two are 54 watts, i cannot notice a difference in brightness but i am guessing the bulbs on the 54 watt ballasts will have a little shorter lifespan