Inspired by funny post written by @przemko about difference between man and woman in color perception, I decided to describe colors and light in more scientific way. For me this topic is really well known, because few years ago I graduated Wroclaw`s University of Technology in Optoelectronics faculty and after that I worked couple of years in componany which is one of the biggest LCD displays producer.

So in this article I will try to explain you in simple way what is the light, what are the colors and why we can see our world in such many colors.

What is the light?

Did you ever think what is the light? Everyone knows that light is surrounding us during the day, and we have little bit less of it in the night. We know that sun, candles, bulbs, lighters and other sources give us the light. But do you know what is the light? I will try to briefly explain this in this post.

Some time ago 2 physicians made some specific observations. The first one was Mr. Faraday who recognized that magnetism have influence on electricity, and the second physician Mr. Orsted made opposite observation where electricity impacts to magnetism. Some years later Mr.Maxwell from Scotland collect both observation and described relation between electricity and magnetism. Because of him we also know that there is something called electromagnetic waves which exist in nature. So we know that electric and magnetic field can have periodic oscillation and that both are always match together.

Why I started from this short story? Answer is quite simple, the light is an electromagnetic wave. Actually when we are saying about light we are thinking about waves which are visible by human eye. But some scientists describes all electromagnetic waves as a light, regardless if they are visible for us or not.

Visible spectrum

Below you can find graph describing electromagnetic waves. Probably you heard about all of them... who did not listen radio? Who did not use microwave? IR - Infrared, did not you use remote for TV? Or didn`t you heard about UV filters used in shiny days? X rays are widely used in medicine checking what is happening inside our bodies. Visible spectrum is special one for us, because these wavelengths are visible for our eyes instead of others.

If you look at above graph you can see something what looks similar to the rainbow. We can easily distinguish 6 colors: Violet, Blue, Green, Yellow, Orange and Red. All of this colors emitted together will give us just one - white. Coming back to the rainbow, this phenomenon proves us that white light emitted by the sun, is really combined from those 6 main colors (for sure we will have more if we consider colors between). So how it is possible that rain can make this phenomenon? The answer is not such complicated, and it is related with wavelengths. Different wavelengths have different refraction when comes from air to the water, and that is why they are separating when comes through rain drops.

How do we see the colors?

You might wonder why we can see this range of light, but not the other wavelengths. There are two main reasons for this.
First, “vision” usually involves some kind of chemical reaction triggered by light. The carbon-based chemistry of our cells happens to be kicked off by light of around the visible range. Longer wavelengths don't carry enough energy to set off the reactions, while light of shorter wavelengths carries too much energy, and can damage the delicate chemistry of life (which is why ultraviolet light causes sunburn, for instance).
Second, the 400 to 700-nanometre range can travel quite far in water before it gets absorbed (which is why a cup of water looks transparent to us – almost all visible light passes through). The first eyes evolved under the sea, and so this range of light held the most evolutionary advantage, compared with other wavelengths.

We have two different types of sensors which react on the electromagnetic waves. First one are called cones, and second are rods. Cones are one type of photoreceptor, the tiny cells in the retina that respond to light. Most of us have 6 to 7 million cones, and almost all of them are concentrated on a 0.3 millimeter spot on the retina called the fovea centralis. Not all of these cones are alike. About 64 percent of them respond most strongly to red light (L-type), while about a third are set off the most by green light (M-type). Another 2 percent respond strongest to blue light (S-type).

What is interesting and what you can read from above graph is that we are most sensitive on green color, because both M and L=type cones are working when green light is coming to our eye.

Mixing of colors

Probably you remember from school that when you will mix some colors then you create new ones. For example when you will mix yellow and blue then you will get green. But this rule is correct only when you merge paints together. But not when you mix lights as a sources. Just take a quick look here:

What you can see on left side calls additive mixing and on right side you have subtractive. Remember when you mix sources you always do additive mixing, more colors means more energy of light. All TV sets, projectors and other displays work by additive mixing. But when you mix paints, each one absorbs light, so you have less light and color is darker. And if I already mentioned about colors absorption, you need to know that every object, which does not emit the light, has color because absorbs some wavelengths from visible spectrum and reflect some others. When light hits an object – say, a banana – the object absorbs some of the light and reflects the rest of it. Which wavelengths are reflected or absorbed depends on the properties of the object. For a ripe banana, wavelengths of about 570 to 580 nanometers bounce back. These are the wavelengths of yellow light. The light waves reflect off the banana's peel and hit the light-sensitive retina at the back of your eye.

To be continued...

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sources:
livescience
wikipedia
ivyroses
andor

pictures:
bulb
colors mixin
electromagnetic wave
cones response
visible spectrum
rainbow

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