Sun is the main source of energy for all living organisms. Light is a kind of energy that travels in the form of electromagnetic waves. It also acts as beam of particles of different frequencies called visible light that ranges from about 400 to 750 nm in wavelength.

The total amount of sun light which enters our atmosphere, about half of it reaches earth surface. The rest is absorbed, reflected and scattered in the atmosphere. Of the total sunlight that strikes the green plants only about portion is used in the photosynthesis. This small portion of sun light sustainsall forms of life on earth. There are two types of photosybthetc pigments i.e chlorophylls and carotenoids. Chlorophylls absorb mostly blue wavelengths (390-430 nm) and red wavelengths (670-700 nm). Green wavelengths are mostly reflected therefore chlorophyll appears green. The carotenoids which are called accessory pigments absorb light in the visible spectrum ranging between 500 nm and 600 nm in wavelength.