In recent years, with the rapid development of facility agriculture, more and more research on plant lighting has been made. LED light source has been widely used in the field of plant lighting because of its unique advantages. Since plant growth has certain requirements on the optical parameters of the light environment, it is necessary to have corresponding measurement techniques and instruments to accurately measure whether the optical parameters of the light environment meet the growth requirements of the corresponding plants, thereby selecting a suitable light source and determining the light source. The quantity and arrangement provide a suitable solution for the development and application of light sources according to the reasonable demand of plants for light.
When used in plant cultivation lighting, LED lighting products should not only consider its basic luminosity and radiance properties but also consider the photon density and plant luminosity of the plant surface in light quantum systems and plant photometric systems according to the photosynthesis characteristics of plants. Learn parameters to comprehensively evaluate the performance of plant lighting sources.
Key factors in plant lighting and requirements for lighting products
First of all, the quality of light. Plants generally rely on chlorophyll in the leaves to absorb the illuminating light, and the absorption band is generally in the blue and red regions, as shown in Figure 1. Absorbed light is converted into organic energy by photosynthesis in plants for growth and reproduction. Therefore, for plant lighting products, the irradiance of the absorption band should be considered first, generally, the irradiance of 400nm~500nm blue light and 600nm~700nm red light band, and the spectral composition and range of the selected combination plant illumination need to be determined. Peak wavelength and color temperature, etc.
Second, the optical density. Plants receiving different optical densities will directly affect the growth and structural characteristics of plants. If the optical density is weakened, there will be a decrease in the same crop, delayed flower bud differentiation, and dysplasia of the ovary. Because the response characteristics of plants and human eyes to the spectrum are different, the human eye’s perception of light is generally measured in the photometric system, while the photosynthesis of plants is generally measured and evaluated in the optical quantum system and the plant photometric system. The evaluation parameters are Photon Flux Density (PPFD). Through a large number of studies, Mc. Cree has shown that the effective radiant energy of photosynthesis can be compared with the actual photobiological effect by using the optical quantum flux density between 400-700 nm.
Again, the light is uniformity. Since the LED illumination has strong directionality and there may be uniformity of spatial light color distribution, in the case of large-area planting, the uniformity of the irradiance of the illuminated surface of the plant should also be investigated to obtain a high-quality uniform illumination environment.
Finally, the long light time. Different plants have different spectral requirements, and different growth stages require different spectra. Artificial light supplementation in facility agriculture must follow the photophysiological properties of plants to achieve the best light-filling effect. Therefore, it is not only necessary to accurately measure the spectral composition of the LED light source, but also to know how the illuminance changes with time.
Measurement of LED lighting products for plant growth
In the past, in the field of plant lighting, photon quantum meter is often used for measurement, but the matching of spectra is difficult to achieve perfect matching, and even the mismatch will be relatively serious, which has a great influence on the measurement accuracy. With the development of spectrometry technology, measurement technology and equipment based on spectroscopy are becoming more and more mature and gradually applied to the field of plant lighting detection.
The spectral corresponding curve of plant photosynthesis is different from the spectral light efficiency curve of the human eye. Therefore, when evaluating the illumination effects of various light sources, the irradiation effect should be evaluated according to the spectral response curve of the plant. The spectroscopy method not only does not have any mismatch problem but also can evaluate the performance of light quality, optical density and illumination uniformity of the illumination product in the whole spectrum. However, the general spectral measurement has problems such as poor linearity and stray light, which limits the accuracy of the test and imposes new requirements on the measuring equipment.
The performance evaluation of LED plant lighting products involves multiple metering systems, with many evaluation parameters and narrow spectrum. Whether it is for test hardware or software, such as matching of optical radiation detectors and spectral measurement. Precision, etc.
LED plant lighting manufacturers and related scientific research institutions should select appropriate measuring schemes based on their own or standard requirements, based on the influence of light on plants, comprehensively and objectively evaluate the performance of LED plant lighting products, and then design plant growth lighting systems. Or fill light scheme to achieve green lighting and efficient lighting.