Question: What happens in your eye that allows you to see colours not black and white and also how does your eye see the light that is being reflected off an object?

Julian Onions answered on 17 Nov 2014:

Good question, but its all a bit complicated.

Light carries energy, and that energy can be caught and changed.
So in your eye there are certain chemicals that are just right for catching particular wavelengths of light. If a wavelength of red light happens to hit one of these chemicals, it makes it change its shape.
This results in a nerve signal that goes off to your brain saying I saw something and it was red.

You also have blue and green chemicals, so you can see red green and blue in all. The cells that contain these chemicals are called cones, because they look a bit like an ice cream cone.
The signals from these cones are combined in your eye, in quite complex ways, and further processed by nerves before getting to the visual cortex, the part of the brain where you interpret vision, and that decides what you see.

You also have other cells called rods, which are very sensitive to light, but only to one colour. These are what you use at night – and because they only see one colour, your night vision is effectively black and white.

A similar sort of thing happens in cameras, in old film cameras it was a direct chemical reaction. Now we use CCD chips, and they convert light particles into electrons directly that we can measure.

We see light either because something emits it, like a star, because it is hot enough to generate it, or because the light from something else hits a surface and is reflected off it. Most objects reflect some light, and we even have a word for how much light an object in space reflects – called the albedo.