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The Effects of Different Light Waves or Light Spectra on Photosynthesis

Photosynthesis is the process where plants, algae and bacteria absorb sunlight, convert it into chemical energy and store it as sugar. The reaction takes place in chloroplasts, cell subunits or organelles in a plant or algal leaves and stems, or in the cell membrane, an exterior cell layer, of photosynthetic bacteria. Sunlight contains 4 percent ultraviolet radiation, 52 percent infrared radiation and 44 percent visible light. Chloroplasts do not absorb all light wavelengths equally.

Pigments
- Chloroplasts and cell membranes in plants, algae and bacteria contain a variety of pigments that react with a narrow part of the visible light spectrum and reflect other colors. Chlorophyll is the most abundant pigment and absorbs blue and red light. It reflects green light, making plants with this pigment appear green. Carotenoids reflect the red, yellow and orange part of the spectrum and absorb blue light. Phycobilins are water-soluble pigments that reflect either red or blue light.
Blue Light
- Blue light has the shortest wavelengths and highest energy of the visible light spectrum. It is the greatest stimulant for chlorophyll to encourage leaf and stem growth. Carotenoids absorb blue light during fruit ripening and leaf fall.
Red Light
- Red light has the longest wavelength of the visible spectrum and lowest energy. Chlorophyll absorbs red light although not to as high a degree as its blue light absorption. Red light absorption by pigments promotes seed germination, flowering, root, tuber and bulb development.
Green Light
- Although green light is absorbed only weakly by plants and other organisms during photosynthesis, the small amount is a strong driver of the photosynthetic process within cells. Some algae appear black or brown because they contain the carotenoid pigment fucoxanthin that absorbs green light. These algae grow in water depths of about 900 feet where the available light is less than 1 percent of visible light at the land surface.
Ultraviolet
- Ultraviolet (UV) radiation has a shorter wavelength and higher energy than blue light. It has too much energy for the plant or organism to absorb during photosynthesis so it develops mechanisms to protect itself. The plant activates a secondary class of pigments, flavonoids and anthocyanins, to absorb the UV radiation and protect the photosynthesis process.
Infrared
- Infrared radiation is heat rather than visible light. It has a longer wavelength and less energy than red light. Infrared radiation occurs in the deep ocean near geothermal vents. These are locations of high heat flow within the Earth̵7;s crust and associated with volcanic activity. Bottom-living bacteria such as green sulfur bacteria, which inhabit the ocean floor at water depths between 400 and 8,000 feet, generate energy by photosynthesis of infrared radiation.

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