Obviously we have to understand a few things about light, since photosynthesis involves a transformation from light energy to chemical energy. 
What we call visible light is only a tiny fraction of a much larger electromagnetic spectrum, shown in part above. This figure greatly exagerates the size of the visable spectrum. The wavelength of light is typically measured either in Angstroms(Å) or in Nanometers(nm). An Angstrom is 1/10,000,000,000th of a meter; a nanometer is 1/1,000,000,000th of a meter. So a nanometer has 10 angstroms. 

The one meter wavelength is to the right in the T.V. radio wave region. 
 

Notice that as the wavelength decreases the frequency increases. and the amount of energy contained by the light increases. Thus ultraviolet light, the light responsible for sun burns has a higher frequency, shorter wavelength and more energy that does violet light. In contrast infrared radiation, has much less energy compared to an equivalent intensity of UV radiation. 

By the way light can be thought of as either a packet of energy or a wave. Light viewed as packet of energy is called a photon. 

pgd revised 2/17/01