Stanley Electric Co., Ltd., through joint research with a research group at the University of Tokyo, has demonstrated for the first time in the world that plant cultivation using red laser diodes (LDs) exhibits growth-promoting effects that exceed those of conventional light-emitting diode (LED) light sources.
This research focused on the potential application of laser and optical device technology to the agricultural field, with the aim of establishing high-precision plant cultivation techniques. The results of this research were selected as one of the "Top 10 Agricultural Technology News of 2025" by the Ministry of Agriculture, Forestry and Fisheries.
Background
In recent years, interest in and expectations for plant factories have grown amid growing risks such as climate change and a declining agricultural population. However, the profitability of production costs, including energy costs, has become a major issue in the widespread adoption and expansion of plant factories, with the performance of artificial light sources being a particularly important factor in determining productivity and running costs.
To date, LEDs, which offer high efficiency and excellent controllability, have been the mainstream artificial light source. In this study, we focused on LDs, which have seen advances in efficiency, output controllability, and light distribution technology, and examined the feasibility of using LD light for plant cultivation as a new option for improving the productivity of plant factories.
Key points of the research
- The wavelength of red LD that most efficiently increases the photosynthetic rate was identified as 660nm.
- Red LDs result in more efficient photosynthesis than red LEDs of equivalent wavelength
- Red LD activates photosynthesis more effectively than red LEDs of the same wavelength, promoting plant growth more efficiently.
- Red LD is a "more efficient light source with less waste in photosynthesis" compared to red LEDs of the same wavelength.
Summary
In this study, we compared LEDs, the mainstream artificial light source used in plant cultivation, with LDs, which have been attracting attention in recent years, to examine their effects on plant photosynthesis and growth. Red LDs (660 nm) are characterized by their ability to emit monochromatic light that precisely matches the absorption peak of chlorophyll, the main photosynthetic pigment in plants. Figure 1 shows that while LEDs emit light over a relatively wide wavelength band, LDs can output monochromatic light over an extremely narrow wavelength band with high precision.
In the experiment, tobacco leaves were irradiated with monochromatic light from red LEDs and LDs of multiple wavelengths, and the photosynthetic rate, stomatal opening, water use efficiency, etc. were measured. The results showed that under red LD irradiation, the photosynthetic rate* increased by up to approximately 19% compared to when red LEDs of the same wavelength were irradiated.
*An index showing the rate at which plants take in carbon dioxide and synthesize organic matter per unit time. One of the major indices for evaluating plant growth efficiency.
Furthermore, we also evaluated the effects on the growth of the entire plant (dry weight, leaf area, and morphological changes). Figure 2 shows A. Growth status and B. Significant differences between LD and LED in terms of dry weight.
In a 12-day continuous irradiation test, plants exposed to red LDs showed significantly increased dry weight and leaf area compared to those exposed to red LEDs of the same wavelength. Furthermore, physiological stress symptoms such as leaf yellowing and photoinhibition observed with red LEDs were not observed with red LDs, demonstrating that plants exhibit high tolerance to the light environment.
These results suggest that red LDs are promising as next-generation light sources for plant cultivation that can replace LEDs, and are expected to contribute to improving productivity and saving energy in artificial light agriculture, such as in plant factories.
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