So I was sitting and looked at a street lamp outside my house.
It is an ordinary lamp that looks something like that: 
This lamp emits white light and it is about 20 meters from my house. It was very dark outside and the only light that was out there emerged from this lamp.
When I slightly closed my eyes, and made them look something like that : (not my eyes 🙂 
I noticed something very peculiar – I saw two beams of light coming out from the main light source directed up and down, but what realy astonished me was that I was able to see the colors of the rainbow splitting from those beams.
- What is going on?
- How the status of my eyes changes the look of the light emergin from the lamp?
- Why almost closing my eyes creates two "beams" of lights from the lamp?
- Why I can see the colors of the rainbow splitting out from those beams?
Best Answer
My theory would be that your eyelids, like windscreen wiper, wipe away some of the exes water on your eyeball. Due to adhesion between the water and the eyelids the surface of this water is slightly curved near the eyelids and if the eyelids are close enough near each other this surface basically acts as a concave lens, which I tried to demonstrate in the following image:
I also tried to verify this theory by basically making myself cry (don't worry, I did not hurt myself for this or anything, I get watery eyes when I yawn). Now by looking close over my bottom eyelid, while keeping my eye open, I only noticed the bottom beam of light, because only the bottom half of the "concave lens" is in my peripheral vision. Without crying it is visible as well but less obvious.
I do not really see a rainbow very clearly in those beams, but water does has different index of refraction for visible light, also because this is also what causes rainbows to form in the first place.