Some televisions have sleep modes which can be set to turn the unit on or off after a set amount of time or at a specific time. Some people use this to watch TV as they're falling asleep -- the programmed-off will turn the tv off after the user has fallen asleep (if they judged their time to sleep properly).
This is nothing new.
The problem with this method is threefold:
1) The TV may turn off too early, requiring the user to turn the TV back on, jarring the user from a near-sleep state
2) they make a lot of noise when turning off*
3) The sudden lack of sound can be similarly jarring
I propose an IR transmitter and sensor bar mounted atop the TV which faces the user. IR has been experimentally used to detect droopy eyes/sleepy drivers.
The unit would have some decent firmware in a microcontroller which would recognize the states of a user falling asleep (watching for gradually decreasing IR reflection off of the retinas) versus a user blinking/turning their head for a moment. It would only "notice" IR reflections that had human eye-characteristics, such as distance apart, size and number (an overridable 1-eye option will exist for partial oedipal sufferers)
As it noticed the user falling asleep, it would gradually dim the brightness of the TV and lower the volume slowly. Once the user was fully asleep, it would completely switch off the TV, which should turn off more quietly* now that the volume is all the way down.
I recognize that there is at least one idea here that states this problem, however, I believe this solution is unique and stands on its own.
*I still only have tube-tvs. I don't know if flatscreens make a lot of noise when turning off, I'm guessing loud turnoffs isn't an issue with them.