ANSI Lumens, Contrast ratio

[eddiem67]

Can someone tell me which one is more significant, say a room that has windows, do I look for a high contrast or lumens?

[AndrewM]

Lumens is light output, the more lumens the "brighter" the picture. Contrast ratio is expressed as a difference between white and black (and in manufacture specs it's a very best case number).

If you have windows you will need to try and block the light coming from them, especially if the light shines on to the area where the screen would be. Otherwise you'll end up needing some super-light canon type projector (4-5k+ lumens - read: insanely bright when it's dark, and doubles as a small space heater).

To give an example I have a 1,000 lumen projector, and in the room it's in there is a sliding glass door and a glass block window, the window has a piece of vinyl over it when watching movies and the door has verticles on it. With all of that the room is dark enough that you couldn't say read a book, or read the labels on the remote control, read your watch, etc it is still light enough that you can see where you are walking. The picture is still a bit washed out.

One time a few years ago somebody gave me the following example, look at your wall/screen in the light you have to work with, that is the absolute best black level you will have on the screen when projected (it will actually be a little worse than that). However one thing that wasn't mentioned is how your eyes will play tricks on you, with all of the other colors on the screen what would otherwise be noted as a white wall will "look" black because of those surrounding colors. It's a similiar trick to the attached picture;

Andrew