How Do Mere Mortals See?There is one important aspect of human vision. In order to see an object, light has to go from that object to the eye (light in the visible spectrum). The light from that object can be either reflected light or the object can emit its own light. But either way, the direction of this light is from the object to the eye. This is important. The eye is only a receiver of light—there isn’t some type of “vision ray” that shoots from the eye. I only point this out because it’s actually an idea that some people have about light. Ask yourself this question:
You are in an absolutely dark room (with zero light sources) for some extended period of time. What do you see after a while?The answer is that you will see black and nothing but black. Black is the color our brains associate with the lack of light. However, many people will give an answer that you will some some stuff after your eyes adjust.
What About X-Ray Vision?We can make X-ray images. That’s not science fiction. Here’s how it works. If you take high speed electrons and shoot them at a metal surfaces, you can produce X-rays. X-rays are just like visible light except they have a much shorter wavelength (but they are still electromagnetic waves). But since X-rays have a different wavelength (and frequency) they interact with matter differently than visible light. This means that some materials (like human flesh) are partially transparent. You can use this to create an X-ray image by shining X-rays through a human and putting an X-ray detector on the other side. The X-rays don’t pass through bones as much as flesh, so you can get an image. So, how could this work with Superman’s vision? If his eyes could detect X-rays like humans detect visible light, he would still need an X-ray source.
Could these same X-rays come out of his eyes (or other parts of his body)? Sure, but in that case he would be detecting X-rays that are deflected from these human tissues, not the ones that pass through. I’m going to guess the intensity would be a bit lower. Anyway, this would be the human equivalent of having flashing lights in your eyes.