Edmonton,
Rainbows and DLPs, for some, go hand in hand. There are a couple of recent posts on the forum with some ideas about how to ameliorate this artifact. Here are some suggestions with respect to the LT150 from someone who hardly ever sees them, so take them with a grain of salt.
1. Mask down the size of your screen or sit further back so that you do not have to move your eyes much to follow the action.
2. Cut the contrast a little at a time and see if this helps.
3. Turn off the "white segment" (projector options, page four - I think).*
4. A grey screen might help, but I think with this projector there's a big trade off with loss of vitality vis a vis colour and also a loss of "punch".
5. Try a better feed - I guess you have already tried a progressive scan DVD player (this makes a very large difference for many). Next you could try a HTPC, but if this doesn't help then I think you're out of luck so -
6. Go with a different projector.
Rainbow, I guess, is as big a problem for you as the grid or "screendoor" effect is for me. When I first had the LT155 in my home theatre I expected it was the one to beat and had been told that it would be the one I would like. I loved it, except for the screendoor effect - it was a deal killer for me just like rainbow may be for you! Some people don't see the screendoor effect until it is pointed out to them, just like rainbows, however, once you see it you'll always see it. With the new DLPs rainbow shouldn't be a factor - problem is these things are expensive and it may take awhile before this technology filters down to products with more consumer friendly pricing.
If you go with the LT155 seriously consider a grey screen. I am sure that one of the reasons people like grey screens with LCDs is that they help mask the "screendoor".
Everyone visiting this forum have been advised many times over to check out products before buying - particularly "rainbow" with DLPs and "screndoor" with LCDs. Don't complain if you have a problem with either.
* I have been experimenting with the "white segment" on and have a couple of observations. There seems to be an improvement in contrast or crispness, but it comes at a price. I see some (very little) video noise increase, but not really palpable, with the good transfers, and also a rainbow here and there, and that's with my HTPC as the feed.
With the screen I am using the colours seem just as good with the "white segment" on as with it off. I now leave the "white segment" on and only turn it off if the particular DVD I am watching has a problem with video noise.
Cheers,
Grant