The H27 projector does leak a little light out the vents in the front. The good news is that it doesn't hit the screen. What little light that leaks out the front is aimed down (if you are on a table, or up on your ceiling - if the projector is ceiling mounted (for you novices - when ceiling mounted projectors are mounted upside down). The amount of light leak is small and since the projector normally sits at least as far back as the audience, it should be not be an issue at all.
AI (Artificial Intelligence)
Optoma says their AI circuitry which looks at the content "frame by frame" and adjusts output to optimize picture quality, increases their effective contrast all the way up to an impressive 4000:1. As mentioned earlier, "AI" type circuitry is appearing in more and more home theater projectors, and the overall result is to provide a better viewing image.
Like almost all lower cost projectors, Optoma's H27 projector does not have adjustable lens shift. This means that you will want to mount the projector (ceiling, shelf or table) at the correct specified height relative to the screen. The Optoma H27 will position with the center of its lens above the top of the screen or below the bottom, typically by a half foot to perhaps less than 2 feet, depending on the size of screen and the position of the zoom. This is, overall, what you want in a fixed lens shift projector, a good angle for most rooms. If you have a low ceiling, you will have to mount the top of the screen still lower, which could be a problem, especially in some basements.
Optional Wide Angle Lens Adapter.
Because the Optoma has a pretty long throw zoom lens, it sits further back than many projectors. If you need it to be positioned closer, a 0.8x lens adapater is available, and it will let you move the projector 20% closer.