Design and application of plant supplemental light with the intelligent laser

Light is one of the most important influencing factors on plant growth. Light environments have also a significant impact on plant growth and development. In the absence of natural light, crops in many areas can suffer from long harvest cycles, low yields and poor quality. Fortunately, light-supplementation devices have been invented to supplement the light for the crops. Among them, the light-emitting diodes (LEDs) have been the main light source for the plant-filling light. But the conventional LEDs can not fully meet large-scale production in recent years, due to the limited lighting range, low efficiency of electricity-light exchange, high cost of line installation, and limited usage environment of light filler for plants. It is particularly important to develop a new light source for plant filling. Compared with the commonly used light sources, laser can be expected to the strong directionality, excellent monochromaticity, strong coherence, and high brightness. Moreover, lasers have been widely used in various scientific and technological fields in the past few decades, such as medicine, material processing, and communications. The lasers can also be used to improve the germination rate and the quality of seeds for the better growth and development of plants, even to delay the decay of plant fruits. In this study, the laser diode (LD) was selected as the light source of the fill light device, in order to design a plant light filler with the intelligent laser. The light source module was used as 35 LDs with wavelengths of 450 nm (blue light) and 660 nm (red light). A heat sink was also designed with the aluminum alloy, in order to ensure the output power and wavelength. The reason was that the LDs generated high heat when working for a long time. The laser driver circuit achieved the adjustable LD drive current, that is, the output power of LD was adjustable. The light intensities of red and blue lights were adjusted to set the light-matching ratio. The laser plant light filler was tested using an adjustable direct current (DC) regulator with a voltage of 24 V, a current of 1.6 A, and a power of 38 W. The photosynthetic photon flux density (PPFD) of the laser plant light filler was measured using a sensor for a total of 16 tests, with an average value of about 55 µmol/(m²·s). An experimental and the control group were set with the "Red Face strawberry" as the subject of the supplemental light test. The control group received the natural light, while the experimental group received the laser supplemental light of 80 cm above the strawberries for 4 hours from 06:00 pm to 10:00 pm every day until the strawberry fruits ripened. Twelve strawberries were randomly selected from the experimental and control groups and then examined for the leaf thickness, chlorophyll content, fruit firmness and sugar content. The results show that the leaf thickness and chlorophyll content of the plant increased by 6.6% and 10.5%, respectively; and the hardness and sugar content were significantly improved by 20.2% and 15.5%, respectively, compared with the natural light. The light-supplementation device can be expected to promote the growth, development and quality of fruits, particularly on the precise adjustment and uniform light output. The compact structure and fine waterproof properties can greatly contribute to the field of plant light in agricultural modernization.