COLOUR
One of the main features of light is colour. If light were just pure white, our whole world would be black and white and shades of grey. But white light is not pure. It is a mixture of all the colours of the rainbow which are known as the spectrum of light.
Colours exist because light is in the form of waves and not all the waves have the same wavelength. Some are slightly longer than others, and these we see as red. Light waves of medium wavelength appear to our eyes as green. We see the shortest light waves as violet. A leaf is green because its surface absorbs all the colours in white light except green, which it reflects into our eyes. A red flag absorbs all colours except red. Objects that reflect all colours are white.
The colour wheel shows how the different colours of light add up to make white light. When you spin the wheel the colours whirl around so fast that the eye cannot follow them. Inside the eye each colour merges with the others so the eye sees all the colours at once – and all colours of light added together make white light.
The different colours of light are seen when white light is split up using a prism, an angled block of transparent material such as clear glass or plastic. As the light waves pass into and then out of the prism they are bent or refracted. Longer waves of red light refract least. Shorter waves of violet light refract most. The other colours spread out between. A raindrop works as a natural prism. Millions of raindrops split sunlight and form a rainbow in the sky.
ADDING COLOURS
We see colours in books and on screens such as the television, in different ways. A television or computer screen has thousands of tiny dots that glow and give out light. These dots have actually only three colours – red, green and blue. These colours are known as the primary colours of light. Added to each other in different combinations and brightness they can make any other colour. For example, red and green together make the colour yellow. Red and blue produce the pinky colour known as magenta. Blue and green form cyan, a type of turquoise. The three primary colours of red, blue and green added together make white light.
On the screen of a computer or TV the dots are arranged in groups known as pixels. The different colours of dots flash on and off in different combinations and shine with different brightnesses. From a distance, the eye cannot see the individual dots. They merge to produce larger areas of colour. When all the red dots on an area of the screen shine, that area looks red. When all three colours of dots in an area of the screen shine brightly, that area looks white. Also the dots flash on and off many times each second, again too fast for the eye to follow. So they merge together in time to produce multi-coloured, moving pictures.
SUBTRACTING COLOURS
Coloured pictures in a book are made like those on a screen, using tiny coloured dots that merge together. The dots are inks made with coloured substances called pigments. There are three primary pigment colours – yellow, magenta and cyan. They work in the opposite way to light colours. They do not add together, but take away or subtract. A yellow dot takes away all colours of light except yellow which it reflects. The other two dots do the same for their colours. By taking away individual colours, the dots merge to produce areas of other colours. All three dots together make black.
The wolf’s mask is realistic and frightening. Yet it is printed using tiny dots of only three colours. They can be separated as magenta, cyan and yellow. To save on coloured inks some parts of the page, like these words, are printed with ready-made black ink.
Picture Credit : Google