Your seemingly simple questions are actually quite muti-faceted. To give you a reasonable answer you'll have to supply more information about the room you intend to use.
- how big a screen do you want to have
- what is the ambient light condition of the room ( total blackout to no light control )
- what type of material do you want to watch ( mainly movies or tv or games )
The brightness you see from the screen is dependent on the projector lumens, how much zoom you use, the size of the screen, the type of screen material, the ambient light, and what type of content.
First off, 30 to 40 feet is a VERY long throw for most HT projectors. The current crop of LCD's with the largest zoom range would throw a minimum of 150" diagonal image at 30' ... 200" diagonal at 40'. Ceiling or table mounting in the range of 10 to 20' from the screen is the normal.
Brightness depends on so many factors it's hard to comment without knowing more. Light reflected off the screen is measured in foot Lamberts. Foot lamberts are calculated by taking the lumen ouput of a projector, and dividing it by the square footage of the screen. Even this is deceptive, as most manafacturers overstate the lumen output of the projector, and also that output is usually in the highest output mode, which has the least accurate colour.
Projector lamps also dim to half their output by end of life, and that has to be considered too. Projectors with large range zoom lenses also generally output close to half their rated output when in full telephoto position ( smallest image - farthest away )
In a blackout condition ( like a movie theatre ) you aim for 12FL from the screen. In a room with ambient light you'd have to triple that to get a watchable image for TV material.
So, give some more details, and I'm sure the memebers here can give you some recommendations.
The 'Is LCD or DLP the way to go' question is surely why you didn't get any responses. While a seemingly innocent question, there are thousands of threads on the subject here on the forum. You'll be best served by doing a bit of reading.
A forum community dedicated to home theater owners and enthusiasts. Come join the discussion about home audio/video, TVs, projectors, screens, receivers, speakers, projects, DIY’s, product reviews, accessories, classifieds, and more!