Prof. Muni Mahendra Kumar
Sir C.V. Raman, the famous Indian scientist and a Nobel laureate, had made an intensive research on the phenomenon of colour,
Early in the year 1963, Raman commenced a systematic study of the immense array of material available for the study of colour in the shape of flowers and foliage of plant world.
The aim was to determine by factual observations the relation which actually exists between the perceived colour and the spectral composition of the light reflected by or transmitted through the petals of flowers or the leaves of plants.
His recent findings corroborate the Jain view that it is the internal constitution of the object which is responsible for producing colour. We quote here some excerpts from the series of his articles on 'The New Physiology of Vision'.[1]
He observes: "The outcome of the investigations was to establish the fundamental thesis that the primary physiological sensations are those excited by monochromatic radiation and to show that the sensations excited by polychromatic radiation are not determinable by simple additive laws. The so-called trichromatic hypothesis and the ideas regarding colour synthesis based on it were found to be definitely contradicted by various facts of observation."[2]
Explaining the phenomenon of colour, he writes: "That the sensation of colour arises from and is closely related to the corpuscular nature of light is evident from the progression of colour observed in the spectrum. When white light emitted by a solid body held at a high temperature is analysed by passage through some dispersing apparatus e.g. a prism or a diffraction grating, it appears spread out into a continuous band of colour. If the dispersion of colour is adequate, a great many different colours may be distinguished in it. These colours form a continuous sequence, and since the light isolated from a sufficiently narrow region of the spectrum consists of corpuscles all having the same or nearly the same energy, it follows that each specific colour observed in the spectrum corresponds to a distinct set of corpuscles all having the same or nearly the same energy. The association thereby made evident between the energy of the light-corpuscles and the colour sensation excited by them is clearly of fundamental nature. It has, of necessity, to form the basis of any attempt to ascertain or elucidate the nature of the sensations of colour.
A chromatic sensation being a matter of subjective perception, it is essential to provide a means of ensuring that the experiences reported are not of an illusory nature."[3]
Further, he maintains: "The differences in spectral character of the light which reaches us, either from the original sources, or from the objects which reflect, scatter or diffuse the light falling on them is likewise the basis on which rests the special faculty of colour perception. The corpuscular concept, on the other hand, is essential for the consideration of all phenomena in which there is transference of energy of radiation to or from material bodies. The emission and absorption of light are examples of such phenomena, and they can be successfully described and explained only on that basis.........
"It follows that all aspects of vision including the perception of space and form, the perception of luminosity and the perception of colour, can only be understood in the terms of the corpuscular concept of the nature of light."[4] Again, he clearly states: "....... colour as seen in daylight is the sensation resulting from the synthesis by the eye of the whole spectrum of radiation falling upon the object and returned to the eye after scattering or diffusion by the material of which it is composed."[5]
It is also shown by Raman that the quantity of light too plays an important role in creation of the chromatic sensation. He writes: "Remarkable changes in our ability to perceive colour follow as a result of lowering the level of illumination of the objects under view. The factor which determines the observability of colour is the magnitude of the light-flux which reaches the eye of the observer.......[6]
All objects which are brilliant red in colour become black and are practically invisible in dim light. Per contra, all objects which are white in bright light continue to be white in dim light.[7]
Thus, we may conclude that according to Raman, the chromatic sensation (i.e. the perceived colour of Cp in our notation) depends upon-
- The energy of light-corpuscles reflected or transmitted by the body, which is ultimately dependent on the material of the body,
and - the light-flux reaching the observer.
It can, therefore, be said that the material composing the body is the deciding factor in creation of the perceived colour. The various colours exhibited by the different flowers or the leaves of the plants are attributed to the specific chemical compounds constituting them. This would become clear from the following statement of another famous Indian scientist Prof. T. R. Sheshadri of University of Delhi, who observes in his article on "Chemistry of Flower Colours": "Greater contributions to the bright yellow and orange shades of flowers are made by carotenoids. However, there are others equally important. In recent years, the deep colours of flowers of Butea frondosa (palas), Cosmos sulphureus and others have been found to be due to the presence of Chalkones and a closely relaxed group called aurone........
As already mentioned, the most important are the anthocyanin which are responsible for the bright red, blue and intermediate shades........
"In the study of the colouring matter of flowers, we have been interested in the chemical structure and the large variations it can undergo. The effect of the structural variations on spectral properties has also been followed up just as in the case of all dyes?"[8]
