Visible light ranges from the wavelengths 400 nm to 700nm, although this may vary between individuals. The wavelength range of 380 nm to 740 nm is typically referred to as Photosynthetically Active Radiation (PAR). PAR is the portion of the electromagnetic spectrum that plants use to achieve photosynthesis. 


Wavelengths in the spectrum and their quantum energy have an inverse relationship. This means the higher the wavelength the lower the quantum energy and vice versa. For example the blue wavlengths (400nm-470nm) contain more quantum energy than the red wavlengths (610nm-700nm).


Photosynthesis is the ability of plants to absorb the energy of light and convert it into energy for the plant. To do this, plants have pigment molecules which absorb the energy of light. The pigment responsible for most light-harvesting by plants is chlorophyll.