When you fall asleep, it usually happens rather unexpectedly. When next I wake, I can't recall exactly when I fell asleep.
When you close your eyes and relax, your eyes tend to roll up slightly behind your eyelids. You can tell someone is faking being asleep if their eyes are looking forward when you open their eyelids, either that or they died suddenly.
When you close your eyes while you are awake, you have nothing to look at but the darkness inside your eyes.
Astronauts on Apollo missions reported occasionally seeing white flashes. These were small gamma ray bursts that penetrated their bodies and stimulated the receptor cells in their eyes, not through the iris of their eyes, but unfocused, through the tissue.
Lying in bed with my eyes closed at night trying to sleep, I sometimes perceive extremely faint aurora-like clouds, the kind one sees when one is standing on the ground at night, directly under an aurora borealis. From a distance, the aurora looks like curtains from space, but when you are directly beneath, as I was one summer long ago in Northern Michigan, it looks like nothing I can describe in daylight. It's so faint, however, I almost dismiss it as my imagination, but it's enough to keep me from falling asleep.
It's been years since I've sensed this phenomenon, probably because I have so much to think about lately that I can't reach that state of relaxation anymore.
The kind of energy that would cause the rods and cones of the retina to be stimulated to such a degree would need to be along the electromagnetic spectrum outside the visible light range of about 400 to 800 nanometers. For the wavelengths to trigger a non-light response in the cells, they would need to be some kind of harmonic equivalent that is carried along a lower wavelength. Or, since gamma rays are on an extremely high wavelength, there would need to be a tonal interference pattern that would bring the wavelength down to at least a partially visible range.
Extra terrestrial communication over extreme distances would require energies well beyond light-speed, plus consideration for the visual sensory organs of the creature to which one wants to communicate. One would need to know how to use the atmosphere of the creature to create the harmonic frequency changes necessary for the transmission to become visible.
Adjustments could only be made if one could see the behavioral response to the transmission by the creature. If the creatures don't perceive the signal as an overt communication, they may react with mass hysteria to what they might assume are conditions in their own environment, or in their own minds. That might be a good invasion strategy.
Occasionally, I'll close my eyes and in the darkness I'll see, or sense rather, an extremely faint image of a face, someone or something, not looking directly at me, but looking down or slightly away at something else. Some kind of face that my mind can only partially piece together from my own memories, but fragmented because the actual image, should I be able to see it for real, might be something I could never describe in nature.
If you ever see something like this when you are trying to sleep and your eyes are closed, do not let it look at you. Open your eyes if it starts to look at you.