It is a perpetual source of natural energy that, along with other forms of renewable energy, has a great potential for a wide variety of applications because it is abundant and accessible. Solar radiation is rapidly gaining ground as a supplement to the nonrenewable sources of energy, which have a finite supply. Recent developments in the areas of photochemistry and photobiology have also helped in bringing attention to solar radiation. In contrast, the vital phenomenon of photosynthesis is an example of the beneficial effects of sunlight in the natural environment.
Solar radiation has, therefore, a prominent ecological role.
Most photobiological investigations have been confined to laboratory work based on the use of monochromatic UVR produced artificially. Because these model studies do not completely reflect the natural situation, the recent trend is to supplement them with experimental work employing sunlight as a natural UV source. This gives results with more realistic, practical values. However, the polychromatic nature of solar radiation, its variable intensity, and the limited knowledge of its distribution at the local level tend to hamper such efforts and complicate the interpretation of the results. The electromagnetic radiation emitted by the sun shows a wide range of wavelengths.