The use of projectors for digital signage has always been limited by a couple of critical factors: the short lifespan of the bulbs, and the cost of servicing (mostly to swap those 2000-hour bulbs).
So many people have been watching with fascination as projector systems get smaller and smaller … and smaller.
This is still largely geek-world stuff, so the manufacturers like 3M, Sanyo and LG had demo space in a hall in the back 40 of the Las Vegas Hilton showing early versions of tiny projectors run by LED lights. Some were as small as maybe 5 by 5 by 1 inch, but they pushed out what looked like a pretty nice video image. However, it had to be done in a very dark room, as these early models can only push 150 lumens, which is maybe a 10th of the brightness of most boardroom projectors.
That will change with time though, and just think about the size and features of your first cell phone 10 years ago.
Across the room were little “Pico” projectors by 3M that are only the size of a typical mobile handset and the LEDs and chips inside are indeed meant to go inside cell phones at some point in the next 2-3 years, if not sooner. The problem right now is brightness, as these ones only cranked 10 lumens, which is kinda like lighting a room with a birthday candle.
That will change, as well, and I can imagine how these ultra-small projectors might one day drive screens in odd places.