The effect of light on plants is mainly shown in two aspects: One is to provide radiant energy for photosynthesis. Second, as a signal to regulate many physiological processes throughout the life cycle of plants.
Effects of light on plant growth - photosynthesis and photosensitive pigments
Usually, the growth and development of plants depend on sunlight, but the factory production of vegetables, flowers and other commercial crops, tissue culture and the reproduction of in vitro seedlings, etc. also need artificial light to supplement light, in order to promote photosynthesis.
Photosynthesis is the process by which green plants use light energy through chloroplasts to turn carbon dioxide and water into energy-storing organisms and release oxygen. A key player in this process is the chloroplasts within plant cells. Under the action of sunlight, chloroplasts transform carbon dioxide entering the leaf through the stomata and water absorbed by the roots into glucose, releasing oxygen at the same time.
The light system in which light reactions occur is composed of various pigments, such as Chlorophyll a, Chlorophyll b, Carotenoids, etc. The main absorption of chlorophyll a, chlorophyll b and carotenoid is between 450nm and 660nm in the spectrogram, so as to promote photosynthesis. At present, 450nm deep blue LED and 660nm ultra red LED are mainly adopted in the market, and some white LED combinations are added to achieve efficient LED plant supplementary lighting.
In order to be able to perceive the light intensity, light quality, light direction and photoperiod of the surrounding environment and respond to its changes, plants have evolved a light-sensing system.
Photoreceptors are the key for plants to sense changes in the external environment. The most important photoreceptors in plants are phytochrome, which absorbs red/far-red light.
Photosensitive pigments are a group of pigment proteins that invert the absorption of red and far-red light, participate in the photomorphogenesis and regulate plant development. They are extremely sensitive to red light (R) and far-red light (FR) and play an important role in the whole growth and development process from germination to maturity.
Photosensitive pigments in plants exist in two stable states: red light absorption type (Pr, lmax=660nm) and far-red light absorption type (Pfr, lmax=730nm). The two types of light absorption can be inverted by exposure to red and far-red light.
Studies related to photosensitive pigments have shown that the effects of photosensitive pigments (Pr, Pfr) on plant morphology include seed germination, desulphurization, stem elongation, leaf expansion, shade avoidance, and flowering induction.
Therefore, the complete LED plant lighting scheme needs not only 450nm blue light and 666nm red light, but also 730 nm far-red light. Deep blue light (450nm) and ultra red light (660nm) provide the spectrum needed for photosynthesis, while far-red light (730nm) controls the entire process from germination to vegetative growth to flowering.
There are two effects of 730nm far-red LEDs on plants
1. Shadow avoidance of far-red light at 730nm
One of the most important effects of 730nm far-red illumination on plants is shade avoidance.
If a plant is exposed to the only 660nm of deep red light, it will feel as if it is under direct sunlight and will grow normally. If the plant is mainly illuminated by the far-red light of 730nm, the plant will feel as if it is blocked by the direct sunlight by another higher plant, so the plant will work harder to break through the blocking, which is to help the plant grow taller, but does not necessarily mean that there will be more biomass (biomass).
2. Flowering induction effect of 730 nm far-red light
Another important role of 730nm far-red light in horticultural lighting applications is that the flowering cycle can be controlled by 660nm and 730nm illumination without relying solely on the influence of the season, which is of great value for ornamental flowers.
The conversion of Pfr to Pfr is mainly induced by the 660nm deep red light (representing the sunlight during the day), while the conversion of Pfr to Pr usually occurs naturally at night and can also be stimulated by the 730nm far-red light.
It is generally believed that the control of plant flowering by photosensitive pigments mainly depends on the ratio of Pfr/Pr. Therefore, we can control the Pfr/Pr value by 730 nm of far-red light irradiation, so as to control the flowering cycle more precisely.
3. Customized lighting formula for LED plants
LEDs are used in horticultural lighting and can boost plant growth by up to 40 percent or help control flowering. Because the single LED is independent, it can control the lighting performance in the greenhouse easily.
Photosynthetic Photon Flux LED itself (Photosynthetic Photon Flux, PPF) light efficiency is very high, deep blue (450 nm) and far-red light (730 nm) typical PPF LED lights at around 2.3 umol/J, super red (660 nm) typical PPF LED lights at around 3.1 umol/J, coupled with the wavelength of these a few LEDs and chlorophyll a/b, carotenoids and phytochrome Pr/(Pfr) absorption spectra is very match, can achieve efficient lighting and significantly reduce energy consumption.
LEDs do not emit heat in the direction of illumination and do not damage the plants, and are suitable for top lighting, interior lighting, and multi-layer cultivation, etc. The R/FR ratio is the ratio of red light (660 nm) to far-red light (730 nm). The R/B ratio is the ratio of red light (660 nm) to blue light (450nm). Through the control of R/FR ratio and R/B ratio, the optimal customized light formula for various plants can be achieved.
In order to improve the lighting for plants, Phlizon can provide unique customization services according to the type of plants and the choice of customers.
November 12, 2018
