The electromagnetic radiation consists of electromagnetic waves that can be characterized by frequency or wavelength of oscillations. Most of the electromagnetic radiation from the sun in particular does not reach the earth's surface. Some of it is absorbed in the atmosphere while others are scattered to space. Nonetheless, the most essential part of the electromagnetic radiation, which is the visible light, is able to pass through the atmosphere and reach the surface of the earth.
Visible light is the electromagnetic radiation at wavelengths between 400 nanometres and 750 nanometres. The electromagnetic radiation within this range can be detected by the human eye and is responsible for the sense of sight. The amount of energy depends on the length of the wavelength. The shorter the wavelength, the higher the energy is. Colours also depend on the length of the wavelength. A short wavelength (the 400 nm side) looks blue and a long wavelength (the 750 nm side) looks red. In photosynthesis, red and blue are the most efficient and useful for the light reactions. They are absorbed effectively by the chlorophyll, a green pigment in plants.