## Newtons Color Plate

The exhibit has a rotating disc that has been divided into several sectors. Each sector is painted in a certain colour. On rotating the disc, what we see is a colour resulting from the superposition (overlapping) of all these colours. The resultant colour depends on the colours used in the sectors, the size of the sectors, speed of rotation and the eye of the individual. That is, no two people would sense the same colour.

We have three types of cone cells in our retina, one sensitive to red, other to blue and another to green. All the colours we perceive for different objects are because of the activation of these cone cells by the light reflected from the objects.

The light which we call as ‘white’ comprises of a wide range of constituent colours which are broadly categorized as Violet, Indigo, Blue, Green, Yellow, Orange and Red. This was first demonstrated by Sir Isaac Newton. By holding a prism in the path of the white light entering a dark room, he was able to get the spectrum of white light consisting its constituent colours.

Similarly, by mixing the constituent colours, it is possible to get a sensation of white.

Newton's colour wheel is one such mechanism for the mixing of several colours to perceive a resultant colour.

Here, the different colours occupy sectors of a circle. As the circle is rotated these coloured sectors form images on our retina. The image formed on the retina will be retained by the brain for a fraction of second. If a new image is formed on the retina before the previous one gets erased from the brain, then the brain cannot distinguish between the two and what it perceives is a resultant colour for the entire disc.

This resultant colour perceived by a person depends on rotational speed of the disc, the angles of the sectors, the colours used in the sectors and the light illuminating the disc. Even when all the above factors are the same, different people can perceive different resultant colours. This is because the colour perception depends on the functioning of a person’s eye and brain. Hence, we cannot say that Newton’s colour wheel always gives white as a resultant colour.