570-590 NM : YELLOW
As with green light , chlorophyll A , chlorophyll B , and beta-carotene do not have large responses to the yellow light range . It is the accessory pigments in plants that harvest this range of light energy for photosynthesis .
590-620 NM : ORANGE
Both chlorophyll A and chlorophyll B absorb light from the orange band of the light spectrum . However , it is chlorophyll B that absorbs the most as it is most sensitive to the shorter lengths of red light wavelengths .
620-700 NM : RED
As previously mentioned , chlorophyll A and chlorophyll B have peak absorption ranges in both the blue and the red regions of the spectrum . Chlorophyll A and chlorophyll B have their peak absorptions of red light in the 620-700 nm range . Chlorophyll A ’ s peak absorption lies around 642 nm , while chlorophyll B ’ s peak absorption lies around 662 nm . High pressure sodium ( HPS ), double-ended HPS , and LEDs all target this red range of light and most effectively match chlorophyll A and chlorophyll B ’ s peak absorption range to the red light spectrum .
700-750 NM ( 730 NM ): DEEP RED
Discoveries in the way a plant rests and processes light energy have led to the use of specific wavelengths to help trigger a plant ’ s resting period . An intense exposure to far-red light at the start of the dark cycle in a flowering room reduces the amount of time the plant needs the darkness . In other words , indoor horticulturists can use supplemental far-red lighting systems to stimulate the plant ’ s phytochrome and trick it into resting more quickly . This technique reduces the amount of darkness required per 24-hour cycle . This is an advantage for growers because they can then extend the light cycle without interrupting the plant ’ s flowering response . Additional light hours equate to more energy for the plant , which , in turn , creates more flower growth and larger yields .
Breakthroughs regarding how particular light frequencies affect plant growth are occurring all the time . Our increased understanding of PAR and the peak absorption rates of chlorophyll A , chlorophyll B , and beta-carotene have pushed horticultural lighting technologies to become more efficient and effective . Whether it be UV-B to increase essential oil production or deep red light to extend the lighting cycle in the flowering stage of growth , science has discovered that even light frequencies that fall outside of the PAR range can still be beneficial to plants ( and the cultivator ). Indoor horticulturists have ultimate control over the growing environment , including control over the light spectrum . As our knowledge of the light spectrum and how it affects plant growth continues to grow , there will be an increase in frequencyspecific lighting systems used by indoor growers . As of now , LED lighting technologies hold the most promise for frequency-specific horticultural devices . It ’ s hard to say exactly what the future of horticultural lighting will hold , but one thing is certain : wavelengthspecific lighting systems that enhance quality and increase yield will be embraced by the indoor horticulture community .
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