Is there such a thing as foot lambert being too high? If so, how high is too high? My room deminsions are 14L x 18W x 8H and there are no windows. I am looking to install a 100' 16:9 diagonal screen. At approx 11.5 to 12 ft throw distance I keep coming up with fl close to 30 and in some cases 40. I am having a difficult time figuring out if this is too high. Any thoughts would be appreciated.
There are many factors that can determine whether it is "too bright".
One is whether the lights are out completely in the room. Not everyone likes pitch dark, some like some lights on over the seating area to be able to see remote controls, pick up a drink without knocking it over, etc. so even if it CAN be pitch dark you may not prefer it.
Another is the size of the screen, since dividing a given amount of light over a larger area makes it less intense. You are talking about a 100" which is very small for your room size and is only 30sf in area. You have the space for a 150" screen in your room and at 66sf would be less than half as bright. Given a real-world 1500 lumen projector, you should see 1500/66 = 22 foot lamberts. This is actually about what you want, as you can start in eco mode and be about 30% dimmer or 16fl, and then switch to normal as the lamp ages so you get some of the original brightness back.
The brightness is also affected by the "gain" of the screen material. Gains less than 1.0 will not be as bright as the calculation above. Some grey screens have gains of only 0.6. With a completely dark room -- and dark painted walls and ceilings, right ? -- you have no need for anything other than a plain white 1.0 surface.
Very few people ever decide they chose a screen too large -- we invariably go bigger with our second screen purchase. As long as you are considering projectors that have the necessary brightness -- like the Sony, Epson 5030, or Benq -- I would start with my seating distance and determine proper screen size based on the height being half the distance to the front row of seats. It is especially important not to pick too small a screen if there will be more than one row of seats, because a larger screen will minimize the difference in field of view for movie watchers. For a front row at 12', a 150" screen is about as big as you want to go, but is barely adequate for a second row at 18'.