Here are the seven colours of the spectrum listed in order of their frequency, from the lowest frequency fewest waves per second to the highest frequency most waves per second :. There are three primary colours in light: red, green and blue. Light in these colours can be added together to make the secondary colours magenta, cyan and yellow.
All three primary colours add together make white light. The way coloured light mixes is very different from the way that paint does. When light hits a surface, some of it is absorbed and some of it is reflected. The light that is reflected is the colour of the object in that light. For example, a blue object absorbs all the colours of the spectrum except blue: it reflects blue light. The table gives some more examples, displaying the colour of light shining on an object, the colour s absorbed by an object, the colour reflected by an object in this light and the colour of an object seen in this light.
These cells, working in combination with connecting nerve cells, give the brain enough information to interpret and name colours. Think of atoms like bricks in a wall chemical compound. Imagine throwing a ball into the wall. If the wall is smooth or has sharp corners, the ball may jump back in different directions. However, if the wall is filled with holes, the ball may go through the wall or get stuck in one of the tricky corners, respectively. Same with every surface when light hits it.
The surface may reflect the light back; it can absorb light or just let it pass through transparent things. For instance, the light we get to see, called visible light, is only a fraction of the full range of frequencies. A molecule might absorb photons from anywhere across the whole electromagnetic spectrum, from radio waves to X-rays , but it will be colourful only if there is a difference in how strongly it absorbs one visible wavelength over another.
As it turns out, this is quite uncommon since most molecules absorb light above the visible spectrum, in the ultraviolet range.
So, because electrons in most molecules are bound very tightly, most compounds are white! Some substances have electrons in the right range of binding strength which makes them suitable to use as dyes. One of the first natural dyes is indigo, commonly used to colour jeans.
The problem with indigo and other organic dyes is that it fades away in time because it absorbs energy, instead of reflecting it. In time, bonds break as a result of the damage. Inorganic dyes like pure iron oxide or rust ochre , however, are lightfast and can last for thousands of years.
This is why cave paintings are still visible today! As a conclusion, things do not have color by themselves — only when light energy hits them, we can see colors.
Also, remember our eyes can only see a limited range of colours. 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 colours at night when the light is dim. 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.
These cones have traditionally been known as blue-sensitive, green-sensitive and red-sensitive, but as each cone is actually responsive to a range of wavelengths, the S, M and L labels are more accepted now. These three types of colour receptor allow the brain to perceive signals from the retina as different colours. Some estimate that humans are able to distinguish about 10 million colours. The primary colours of light are red, green and blue.
Mixing these colours in different proportions can make all the colours of the light we see. This is how TV and computer screens work. If you look at a screen with a magnifying glass you will be able to see that only these three colours are being used. For example, red and green lights are used to make our brain perceive the image as yellow. When coloured lights are mixed together, it is called additive mixing.
Red, green and blue are the primary colours for additive mixing. If all of these colours of light are shone onto a screen at the same time, you will see white.
This is different when you are mixing paints. Each colour of paint is absorbing certain colours and reflecting others. Each time another colour of paint is mixed in, there are more colours absorbed and less are reflected.
The primary colours for adding paints or dyes, such as for a computer printer, are yellow, magenta and cyan. If you mix all of these colours together, you will absorb all the light and will only see black, because no light will be reflected back to your eyes. You can easily experiment with this.
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