The study of how and why plants absorb certain wavelengths of light is being carried out by NASA space exploration scientists to agriculturalists specializing in indoor growing. Knowing which wavelengths facilitate plant growth, food production and specific nutrient production can help growers, scientists and even homeowners efficiently produce plants and crops.
Plants respond to the full spectrum of light: from infrared to ultraviolet. In the middle of these two is visible light. Blue wavelengths are short and peak photosynthesis occurs at a wavelength of 430 nanometers. Red wavelengths are longer and peak performance happens at about 660 nanometers. The visible spectrum between blue and red is broadly referred to as green light. While this is the spectrum our vision is most closely attuned to, it provides little to no benefit for plants, according to "Light and Plant Development, Volume 30," a 2007 publication edited by Garry C. Whitelam and Karen J. Halliday.
During the summer, the high sun provides an abundance of blue light wavelengths. This signals the photoreceptors in plants to produce as much vegetative, or leaf and stem growth, as possible. As the sun hovers near the horizon for longer periods going into fall, the light quality shifts to more red light wavelengths. The photoreceptors respond by inducing the plant to produce flowers, seeds, or fruit at the expense of vegetative growth.
Growing plants indoors or inducing photosynthesis during dark hours of the day requires specially designed artificial lights. Bulbs with special fixtures that produce intense light o simulate the sun's blue wavelengths or a mixture of blue and red wavelengths. Because each species of plant has a different response and preference for blue and red wavelengths, it's important to know when to use blue light, red light or a mixture. Imitating the light habits of a plant's native region produces the best results, according to "Light and Plant Development."
Infrared, or very long wavelength light, can induce plants to stop growing or even prevent them from germinating, according to "Light and Plant Development." Ultraviolet light, or very short-wavelength light, can harm plants if they are overexposed, especially to the shortest of ultraviolet wavelengths. Although the Earth's atmosphere filters out most of the most harmful ultraviolet wavelengths, deterioration of the ozone layer has plant scientists worried about Earth's vegetation in the future.
Ultraviolet and far-red spectrum light filters are available for greenhouse use. Far-red spectrum filters help produce more compact plants, while ultraviolet filters help reduce plant pest and disease problems, according to "Light and Plant Development." Netting once used primarily to partially shade plants and protect them from weather or predator damage is produced in specific colors. Each color enhances certain light wavelengths while reducing others, "Light and Plant Development" says.