but also their colours. It may be noted that colour is a psychological property of our sensory experience. It is created when our brain interprets the information received from the external world. It may be remembered that light is described physically in terms of wavelength, not in terms of colour.
As we have read earlier, the visible spectrum is a range of energy ( - nm) that our photoreceptors can detect. The energy lower or higher than the visible spectrum is harmful to the eyes. The sun light is a perfect mixture of seven colours just like a rainbow. The colours observed are violet, indigo, blue, green, yellow, orange, and red, abbreviated as ‘VIBGYOR’.
The Dimensions of Colour A person with normal colour vision can distinguish more than seven million different shades of colour. Our experiences of colour can be described in terms of three basic dimensions, called hue, saturation, and brightness. Hue is a property of chromatic colours. In simple words, it refers to the name of the colour, e.g., red, blue, and green.
Hue varies with wavelength, and each colour is identified with a specific wavelength. For example, blue has a wavelength of about nm, and green of about nm. Achromatic colours like black, white or grey are not characterised by hues. Saturation is a psychological attribute that refers to the relative amount of hue of a surface or object.
The light of single wavelength (monochromatic) appears to be highly saturated. As we mix different wavelengths, the saturation decreases. The colour grey is completely unsaturated. Brightness is the perceived intensity of light.
It varies across both chromatic and achromatic colours. White and black represent the top and bottom of the brightness dimension. White has the highest degree of brightness, whereas black has the lowest degree. Move from a lighted area to a dark room and note how much time you take to see things clearly in that room.
Next time put on red goggles while you stay in the lighted place. Then move into the dark room and note how much time you take to see things