Absorption and Utilization of Light Energy by Photosynthetic Pigments :

 * Chief source of light energy for photosynthesis is the sun

* The earth receives only about 40% (or about 5x1020 K.cal.) of the total solar energy. The rest is

either absorbed by the atmosphere or is scattered into space.

* All the incident light energy falling on green parts of the plants is not absorbed and utilized by the

pigments. Some of the incident light is reflected, some are transmitted through them while only a

small portion is absorbed by the pigments.

* Photosynthetic pigments absorb light energy only in the visible part of the spectrum. However,

certain photosynthetic bacteria use infrared light of comparatively shorter wavelengths.

* Only about 1% of the total solar energy received by the earth is absorbed by the pigments and is

utilized in photosynthesis.

* There is very weak absorption and strong reflection of light by the pigments in the green part of the

spectrum and hence, the chloroplasts appear green in green plants.

* All the pigments except chlorophyll A are called accessory pigments. All the light energy

absorbed by accessory pigments is transferred to chlorophyll a molecule, which alone can take part in

primary photochemical reaction in photosynthesis. Chlorophyll a molecule also absorbs light

energy directly.