Light quality. Plants generally rely on chlorophyll in their leaves to absorb light, and their absorption bands are generally in the blue and red regions, as shown in Figure 1. Absorbed light is converted into organic energy by photosynthesis in plants, which is used for growth and reproduction. Therefore, for plant lighting products, the first consideration should be given to the irradiance of the absorption band, which is generally 400nm~500nm blue and 600nm~700nm red, as well as the spectral composition, range, peak wavelength and color temperature of the selected combination of plant lighting.
Light uniformity. Due to the strong directivity of LED luminescence and the possibility of the uniform distribution of spatial light and color, the uniformity of radiated illumination on the exposed surface of plants should also be investigated in large-scale planting occasions to obtain a high quality and uniform lighting environment.
Optical density. Different light densities of plants will directly affect the growth, development and structural characteristics of plants. If the optical density is weakened, the same crop will be reduced, flower bud differentiation will be delayed, ovary dysplasia and other phenomena. Because the response characteristics of plants and human eyes to the spectrum are different, the light perception of human eyes is generally measured in the photometric system, while the photosynthesis of plants is generally measured and evaluated in the photometric system and the photometric system of plants, and the evaluation parameter is light quantum flux density (PPFD). Through a large number of studies, McCree has shown that between 400 nm and 700nm, the evaluation of the effective radiation energy of photosynthesis by using optical quantum flux density is in good agreement with the actual photobiological effect.
Day long. Different plants have different demands on the spectrum and different growth stages have different demands on the spectrum. The artificial light supplement in facility agriculture must follow the photophysiological characteristics of plants in order to achieve the best light supplement effect. Therefore, it is necessary not only to accurately measure the spectral composition of the LED light source, but also to know the change of illumination with time.
The performance evaluation of LED plant lighting products involves multiple measurement systems, with many evaluation parameters and a narrow spectrum. Both the test hardware and software have higher requirements, such as the matching problem of light radiation detector and the precision of spectral measurement.
