In the growth phase of tomatoes, low light conditions can significantly affect plant development. Therefore, it is essential to optimize lighting during this period. Determining the most suitable and scientifically accurate light levels has been a long-standing research focus among scholars.
The dynamic fill-light system based on fluorescence detection uses the MINI-PAM device to monitor the actual photosynthetic efficiency of tomatoes. It combines LED light sources with precise control mechanisms to guide greenhouse tomato cultivation. This system includes an STM32-based greenhouse monitoring system, a programmable constant current source providing stable power, high-power red and blue LED combined light sources, and the MINI-PAM portable fluorescence detector. The STM32 system collects environmental data, while the MINI-PAM measures fluorescence parameters. Based on these data, the optimal brightness and red-to-blue light ratio for the LED array are calculated. The host computer then controls the current source to drive the LED lights, achieving dynamic fill lighting.
Photosynthesis is fundamental to all biological processes, as plants convert light energy into chemical energy through chlorophyll fluorescence. Over the past three decades, research on LED artificial light sources in horticulture and space agriculture has gained significant attention. Studies show that red light influences plant morphology and leaf growth, while blue light affects stomatal opening and chloroplast development. Combining red and blue LEDs enhances plant growth, making them ideal for tomato cultivation. The system uses closed-loop control via software to analyze tomato growth under optimal lighting conditions.
The system comprises five modules: an industrial server for decision-making, an STM32-based environmental monitoring system, a JBP-7510 programmable constant current power supply, a red and blue LED array, and the MINI-PAM fluorometer. By adjusting the current based on fluorescence parameters, the system regulates the light intensity to maintain optimal photosynthetic efficiency. A schematic of the system is shown in Figure 1.
The JBP-7510 power supply ensures stable current output, critical for controlling LED brightness. With a voltage range up to 75V and current accuracy better than ±0.2%, it meets the system’s precision requirements. Test results confirm its reliability in maintaining consistent current levels for LED operation.
For the LED array design, two configurations were tested: one with a 1:1 red-to-blue ratio and evenly spaced LEDs, and another with a 4:1 ratio, placing the blue LED at the center. These designs aim to ensure uniform light distribution across the tomato canopy.
The MINI-PAM fluorometer communicates with the host computer via RS-232, enabling real-time data exchange for closed-loop control. The software design coordinates the environmental monitoring system, the fluorometer, and the current source to dynamically adjust lighting conditions.
The system continuously monitors and adjusts light parameters, ensuring optimal growth conditions. Fluorescence data is stored and analyzed to maintain desired levels, guiding real-time adjustments. This approach creates a tailored lighting model for tomatoes under varying environmental conditions.
In conclusion, the dynamic fill-light system has been successfully developed, using real-time data from fluorescence measurements and environmental sensors. It adapts lighting based on plant needs, improving growth under low-light and low-temperature conditions typical in northern greenhouses. This system represents a significant advancement in smart horticulture.
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