Have you ever watched videos on smartphone or pad in your bed, and think it would be nice to see the screen bigger, with your hands freely and comfortably lying on bed. Actually many people think just like you, and they have some interesting ideas. Here are some examples from the Internet:
"I don't know if this has ever been mentioned before or anyone has tried it.... but, I'd like to know if it was possible to mount a TV onto the ceiling whereas when your laying down in bed you can just look up at the ceiling and watch it."
-- By Jerky2002 on Big screen forums
"I'm considering building a really weird setup at home: A projector will project on the ceiling above my bed. From the bed, I'd watch movies, read e-books, and even play mouse-only games."
-- By Dan on Tomsharware
"I would like to watch stuff whilst lying down. Any reason why I couldn't simply put a projector vertically and display stuff on the ceiling? "
-- By Elh on Ars technica
"Why has no one made a device to project e-books onto the ceiling? Who wouldn't love to lie in bed and read?"
-- By Deleted on Reddit
Statements above gave me some inspiration, later I started this project, trying to design a ceiling projection device.