What do you need to see?In short, two things: eyes and light. Although this may seem to be self-evident, it contains a basic truth that might be compared to the question of which came first, the chicken or the egg? Apparently there was light before life forms developed eyes to observe something that already existed, namely sunlight. Naturally, the radiation that reach Earth from the Sun contains much more than the wavelengths of light visible to the human eye, but it is in this range of visible light that the amount of radiation is at its greatest – no wonder then that eyes have adapted themselves to it!
The wavelength range of electromagnetic radiation perceived by the human eye as visible light extends from approx. 400 nm to 700 nm (4 to 7 ten-thousandth parts of a millimetre). All in all, light represents only a small part of all radiation that extends from radio waves several kilometres long to radioactive gamma radiation with wavelengths in the region of millionths of a millimetre. Even so, narrow wavelength bands are wide enough to contain the full spectrum of colours from red to blue and violet.
The ability to distinguish colours is the result of individual wavelengths of light being perceived as different colours. Consequently, a colour is a property defined by the senses of the observer, as electro-magnetic radiation in itself has “no colour” and is simply radiant energy. As colour vision is an individual trait, people tend to see colours in slightly different ways. Animals may well perceive a far greater range of colours than humans. Properties vital to each species have been strengthened through evolution. For example, some birds and insects need to detect ultraviolet radiation in order to find food.
Text and images: Sakari Mäkelä, M.A.
(Article in the Tikkurilan Viesti Newsletter, Issue no. 2, November 2004)