I think most people here, including myself and surely eat meat as well, are well aware of this phenomenon. Manufacturers inflate the lumens, and the lumens you get at home with the projector set to optimum picture quality is often 1/3 or less, but we know that say a "1500 lumen" projector will generally give you a bright image in a dark room even though it's not actually 1500 lumens, so on and so forth, we know. When I say 5000 lumens for example, I'm thinking of the manufacturer's inflated number. I'm already taking this in to account.
I think a better response to eat meat, rather than telling him something he already knows, is ask how well that "3500 lumens" projector performs subjectively with ambient light. That's what really matters, after all.