Light as Energy

The energy for photosynthesis is light, typically electromagnetic radiation from the sun. Light behaves as particles—discrete packets of energy called photons and as waves that oscillate along a path.

The wavelength is measured as the distance between corresponding points of two consecutive waves, such as crests. The electromagnetic spectrum includes gamma rays with wavelengths in picometers to radio waves with wavelengths as long as kilometers.

A wavelength is inversely proportional to the energy it transmits. That is, long wavelengths have less energy than short ones.

Although the sun emits a broad spectrum of electromagnetic radiation, only a part of this spectrum, ranging from around 380 to 750 nanometers, is visible to the human eye and can support life on earth.

In plants and other photosynthetic organisms, chloroplasts contain different pigments  that absorb specific wavelengths of visible light. For instance, the chlorophyll a pigment only absorbs red and blue light, causing green to be reflected. This is why most leaves appear green in color. 

Photosynthesis transforms the light energy into the chemical energy stored in glucose and other organic molecules. These molecules serve as energy sources for non-autotrophic organisms in the food pyramid.