[rtkwe]

> large lecture hall, you need a large projection with very bright light for everyone to see.

And the hard limit on how bright you can make that is that the lecturer is staring into that light while writing so you can only make it so bright before it becomes painful or damaging. Anecdotally when I was in elementary/middle school we'd sometimes have to work things out writing on a projector and it was tough sometimes and looking up you couldn't really see because your eyes had adjusted to the brightness of the projector. Maybe they could improve the lenses to spill less light out but it wasn't back then.