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How do we see colour? First of all, light enters our eye through the cornea and into the iris, which is the coloured ring of the eye controlling the amount of light that enters the eye. The light then travels into the lens, where the rays of light will get focussed onto the back part of the eye, called the retina. The retina is a thin layer of light sensitive material that covers the back part of the eye. It is made out of two types of cells, called rods and cones. The rods look like tiny cylinders that detects light. The other type of cells are the cones, which, like their name, are shaped like cones. Cones detect colour. There are three different types of cones. Each type will respond to a different colour, for example, one type of cone responds to the colour red. The other type of cone responds to the colour green. The third type of cone responds to the colour blue. The cells in the retina will then send a electric impulse through the optic nerve when they detect light and colour. The electric impulse will then go to the brain. If there is red, green, and blue light, the retina will send a message to the brain, and the brain will detect the presence of the colour white.
We now know that white light contains all the colours of the spectrum. Still, how do we see colour? Well, we know that when light hits an object, three things can happen to it. Light can be either transmitted, reflected, or absorbed. If white light strikes a red apple, all the colours of light are absorbed by the surface of the apple. Only the colour red is reflected off the apple. The red rays of light eventually reach your eyes, and your brain sense the apple as red since only red rays of light is reaching your eye. Therefore, you see colour depending what colours reflect back from the object. If an object reflect all the colour it hits, then the human brain would sense that object as being white. If you see an object that absorbs all the colours, then the human brain would sense that the colour of the object is black. This explains why the sky is black at night, because there is no light in the night sky that reaches the eye. When no light reaches the eye, the brain sense that it is black.
A television screen works because it has thousands of little groups of phosphor dots on the screen. Each group contains three different types of phosphor dots, one that glows red, one that glows blue, and one that glows green. These phosphor dots glow because they are receiving energy from the electrons that are being released by the picture tube inside the television. If they are not receiving any energy from the electrons, the dots don’t glow and you will see the tiny group of phosphor dot as black. However, if all three dots (green, blue, red) in the small group glow all brightly at the same time, then you will see the group as white. Different colours depend on how brightly the green, the red, and the blue phosphor dots glow. For example, the television screen would make cyan when both the blue and the green phosphor dots glow at the same time inside the group. Most computer monitors also work the same way as television sets do.
The screen of a television has thousands of little groups of phosphor dots.
Click here to learn about the solar spectrum.
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