Where are colors?

 Courtesy: Mosa Farzana Israt, Lecturer in Physics, Dept. of EEE, Green University of Bangladesh

Does light have colors?

Well. Think about our five senses which allows us to interact with the world in various ways. Touch, Smell, Sight, Taste and Sound.

For example there isn't anything called as touch. Your skin is like an input device, like a keyboard, when these keys are pressed, the CPU understands it and processes it. If there was no CPU these keys would be useless. Similarly when you touch something, the input is taken by the skin, which converts it into electrical signals sends it to the brain and ultimately your brain says "I feel the touch" So touch sensation is only in the brain.

Now I know you want to talk about colors and here I am talking about skin. Let’s have a look.

We all know that light is an electromagnetic wave i.e. a combination of electric and magnetic field. Are you see an electric field or magnetic field with color? But there are different color of light red, blue, green etc. As light is just combination of two field, why light have red, green, blue or other color?

One can say it’s all about frequency of light. But I would say frequency is nothing but number of times change in electro-magnetic field.  It’s remain as electromagnetic field, nothing other formulated. But why different color of light exists?

Is color on eye?

In our eyes we have receptors various kinds which get activated by different frequencies of light. There are two types of photoreceptors – rods and cones. The cones detect color. The rods only let us see things in black, white and grey. Our cones only work when the light is bright enough, but not when light is very dim. This is why things look grey and we cannot see colors at night when the light is dim.

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There are three types of cones in the human eye that are sensitive to short (S), medium (M) and long (L) wavelengths of light in the visible spectrum. When photons strike the cone cells in the retinas of our eye they transfer their energy to the electrons in the chemicals contained in the cells. This changes the energy level of the chemicals which leads to an electrochemical reaction that produces an electrical signal i.e. voltage. But we know voltage have no color, so where are the colors?

Actually, different wavelengths of light transfer different levels of energy and cause different reactions and different signals. The brain receives the signal from the nerve, your brain interprets it and tells your mind that you are seeing light of a certain wavelength, or color. So strictly speaking there is no red light or blue light. There is only a 600 nm light or a 400 nm light. Naturally our eyes evolved to detect the most prominent wavelengths of light from the Sun that were most useful to us as hunters and gatherers. Those who saw the colors were more successful at staying alive and reproducing.

Other creatures, see other wavelengths of light as color. Bees for example see colors in ultraviolet light that helps them to identify flowers that are of the greatest value to them. Color vision takes a lot of energy and brain power, so some creatures that live in an environment where seeing color is not important to their survival, do not see color at all. Just varying intensities of light.

In short, the colors are actually assigned to the wavelengths of light by our brain. Colors exist because you have a brain, without brain, there wouldn't be any color.