In Darkened room is it worth to buy dnp supernova(black diomand dalite hp)

No. No matter how good or expensive these screens are, they always introduce some sort of flaw in the image in order to combat the ambient light in the room. The only reason they look like they pop colors is because you're used to seeing a washed out image with normal screens in ambient light, and these screens will preserve the contrast in a room with ambient light.

In a room with no ambient light, a standard textureless white screen will achieve better results, as long as you don't have white walls and ceilings. In that case, a Black Diamond screen, with it's excellent light scatter control, can make a bit of difference, but I am not sure it justifies the massive price difference.

Absolutely. In the mean time, you can see my thoughts on most of the popular ambient light screens out there in this thread:

http://www.avsforum.com/t/1431840/just-received-and-mounted-my-new-dnp-supernova-blade-08-85-screen-pics-and-impressions-inside

I've got a completely light controlled room (basement) with light colored walls and white acoustical ceiling tiles. I bought a Black Diamond .8 gain screen and saw a massive improvement in black level performance. I still can use my old white screen as it is motorized and drops down just in front of the Black Diamond, but after nine months of ownership I haven't watched a movie on it.

From a cost perspective you are better off covering/painting walls and ceiling to achieve better black levels. Having said that, this is something I am not prepared to do. Colors and shadow detail appear excellent to me, and the addition of a Darbee Darblet only makes it better. I've changed my screen four times in the last three years, switched my receiver, and upgraded my projector four times. I would consider a screen like a DNP or a Black Diamond to be a purchase for life, so in that respect it is worth the extra money.

No ambient light addresses only a part of the problem.

Light from the screen can still reflect off of room surfaces and back to the screen, reducing intrascene/ANSI contrast.

That can be addressed with dark room surfaces or the specialized screen.

While true, ambient light rejection screens also introduce other issues, like.... hotspotting, color shifts, sparkles, small viewing angles, etc.

A white or gray screen for a darken room is your best bet.

I believe the convention is that ambient light means light sources other than the pj, so wouldn't include re-reflected light.

I believe the convention is that ambient light means light sources other than the pj, so wouldn't include re-reflected light.