I think we are talking about the differences in the light engines of the LT150/LT155/VT540.
The LT155 and VT540 both use a 130 watt UHP lamp but the LT155 has a micro-lens array (MLA) that both boosts output from 1000 to 1200 lumens, while making the screendoor less intrusive. The light output of both of these projectors is diminished somewhat by being split into three colors, passing through three LCD panels, and then being recombined, in what is called a "dichroic" optical assembly.
The DLP LT150 lamp is 160 watts (of a different lamp type), but it must pass through a color wheel before being reflected off a single DLP panel. The reflective optical assembly absorbs less of the light but the color wheel is the source of the DLP's "rainbows" and relatively low brightness. Each segment of the 4-element wheel is only illuminated 25% of the time (and in actuality somewhat less) and in a home theater application, the clear segment is turned off, so you start with only about 75% of the rated lumens (so the LT150 brightness in a HT application is probably only 600 lumens), and the colors are "strobing" at the speed of the color wheel RPM, and are recombined in your eye with the "persistance of vision" effect. There's the rub, it would seem that some percentage of the population has slightly too little of this "persistance of vision" and thus see the rainbows.
I don't know whether this is related to genetics or age or other factors, just that my wife and myself both do not see rainbows but my kid does. We wear glasses and she does not, and we're each 20-some years older than her. From what I can tell, some minority of the population sees the rainbows, some smaller percentage are painfully aware of them.
Radar, one other thing to consider is lamp cost per viewing hour. By way of comparison, for the three projectors above I checked one source (
www.lowballvideo.com ) and found these figures:
LT150 lamp @ $495. lasts 1000 hours or about $.50/hr
LT155 lamp @ $470. lasts 1000 hours or about $.47/hr
VT540 lamp @ $315. lasts 2000 hours or about $.16/hr
...although you might "shop around" and get a better deal elsewhere.
If you can, try to evaluate all the projector technologies - in addition to LCD and DLP, there are CRT and DiLAs. The DiLA's are $5000 and up used, and the CRTs about $2000 and up used. Frankly, if I had a darker room, I would now own a used CRT, but I'm a "tweeker" from way back.
Lurker #25, I read your thread, and in my opinion there were too many variables in the "shootout". In particular, a different gain screen or a very light-colored decor such as my room might have altered the outcome. I use a DIY matte white surface, I may experiment with gray paint just to see if the blacks improve - it'll be cheap in money and time. However, I can't use a high gain screen because of the 7.5' height of the projector, and some off-axis seating I have. The point is, different rooms with different layouts and different eyes may make different choices. To each his own.
Gary
[This message has been edited by Gary McCoy (edited 08-23-2001).]