In recent years, with the rapid development of facility agriculture, more and more research on plant lighting, LED light source with its unique advantages, so that it is widely used in the field of plant lighting. Because the plant growth has certain requirements on the optical parameters of the light environment, it is necessary to have the corresponding measurement techniques and instruments to accurately measure whether the optical parameters of the light environment meet the growth requirements of the corresponding plants, so as to select the appropriate light source to determine the light source Quantity and arrangement, according to the reasonable demand of light for the development and application of light to provide appropriate programs.
LED lighting products in the use of plant cultivation lighting, not only to consider its basic luminosity, radiation performance, according to the photosynthetic characteristics of plants, in the light quantum system and plant photometric system to consider the plant surface photon density and plant photometric Learning parameters, so as to comprehensively evaluate the performance of plant lighting.
Key factors of plant lighting and requirements for lighting products
First, the light quality. Plants generally rely on chlorophyll absorption in the leaves to absorb light, the absorption band is generally in the blue and red areas, as shown in Figure 1. Absorbed light in the plant by photosynthesis into organic energy, for growth and reproduction. Therefore, for plant lighting products, the irradiance of the absorption band should be considered first, generally 400nm ~ 500nm blue light and 600nm ~ 700nm red light band irradiance, and the need to determine the selected combination of plant lighting spectral composition, Peak wavelength and color temperature.
The absorption spectra of chlorophyll a and chlorophyll b (from CIE 2012)
Second, the optical density. Plants accept different optical density, will directly affect the plant growth and structural characteristics. Such as the optical density weakened, there will be reduced with the crop, bud differentiation delay, ovary development and so on. Because the response characteristics of the plant and the human eye to the spectrum are different, the perception of light in the human eye is generally measured in the photometric system, and the photosynthesis of the plant is generally evaluated in the photon quantum system and the plant photometric system. The evaluation parameters are Light quantum flux density (PPFD). Mc.Cree through a large number of studies show that between 400-700nm, with light quantum flux density evaluation of photosynthesis of effective radiation can be achieved with the actual light biological effects in line with the better results.
Again, light uniformity. As the LED light has a strong direction, and there may be uniformity of spatial light color distribution, therefore, in a large area of planting occasions, should also be observed on the irradiated surface illumination uniformity, in order to obtain high-quality uniform lighting environment.
Finally, the day long. Different plants have different requirements for the spectrum, and the demand for the spectrum is different in different growth stages. The artificial light in the facility agriculture must follow the photophysiological characteristics of the plant in order to achieve the best effect. Therefore, not only need to accurately measure the spectral composition of the LED light source, but also be able to know the illumination changes over time.
Measurement of LED lighting products for plant growth
In the past, in the field of plant lighting, light quantum meter is often used for measurement, but the spectrum of the actual match is difficult to achieve a perfect match, or even mismatch will be relatively serious, a greater impact on the measurement accuracy. With the development of spectral measurement 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 curves of plant photosynthesis are different from those of the human eye. Therefore, in the evaluation of the irradiation effect of various light sources, the irradiation effect should be evaluated according to the spectral response curve of the plant. The spectral method not only does not exist any misalignment problem, but also in the full spectrum of the lighting products of light quality, optical density, uniformity of light performance in all aspects of evaluation. However, the general spectral measurement of linear poor and stray light effects and other issues, on the other hand limits the test accuracy, but also on the measurement equipment put forward new requirements. Remote hand-held SPIC-200 spectrum color illuminometer can solve the above problems.
The SPIC-200 illuminometer solves the problem of spectral mismatch between the traditional illuminance meter and the colorimeter, and achieves the zero mismatch. The SBCT (Spectral-Integral) technology with international patent greatly broadens the photometric range and improves the accuracy. This method combines the integral method and the spectroscopic method to improve the linearity of the spectral measurement by accurate correction of the absolute value of the spectral measurement in order to obtain the accurate performance parameters of the LED plant lighting product. It is the world's most accurate photometric / radiometric measurement method. Its illumination accuracy to ensure that within 4%, the actual illumination measurement range is extended to 0.1lx ~ 200klx, the minimum measurable 0.1lx, f1'≈0, is the world's highest level of similar instruments.
In addition, the use of patented complex variable matrix stray light correction technology, the spectral measurement of stray light control capacity increased by 1 to 2 orders of magnitude, the impact of stray light to do ≤ 0.3%.
Wavelength range: 380nm ~ 760nm
Wavelength Accuracy: ± 0.5nm
Illumination measurement range: 0.1lx ~ 200klx
Accuracy of illumination: ± 4% (reading + 1 words)
Stray light: ≤ 0.3%
Accuracy of chromaticity coordinates: ± 0.001 (relative to the standard source of traceability to NIM stability over ± 0.0001)
By combining the receiver with the space cosine and the intelligent analysis software, it is convenient to realize the conversion between multiple systems. The relative spectral power distribution, photosynthetic irradiance, photon density, chromaticity coordinates, illumination uniformity, peak wavelength, The main wavelength, the radiation intensity ratio of each band, color temperature, color rendering index and other parameters.
Measurable General parameters:
1) relative spectral power distribution P (λ)
2) Spectral irradiance E (λ)
3) Color coordinates: (x, y), (u, v), (u ', v')
4) correlated color temperature Tc
5) Color rendering index Ra, Ri (i = 1 to 15)
6) Color Tolerance SDCM (Macallian Ellipse, Rectangle, and CIE u'v 'Circle)
7) peak wavelength, half width
8) color purity, main wavelength
9) Red ratio
10) light intensity E, radiation illumination Ee
11) More measurement functions can be customized
Measurable plant lighting parameters:
2.Total number of photons on the surface of leaves(Light quantiy/intensity)
3.The illuminance variation with time (Day length)
For the high accuracy of the field measurement, the need for small size, fast measurement of measuring instruments, in order to carry, at any time to read the data. SPIC-200 has a 4.2-inch touch screen, compact design, a very mobile phone grip, a key operation, one step to complete the field measurement and analysis, really called the real-time data read, millisecond precision measurement. Built-in high-capacity SD mobile memory card, intelligent operating system and other modern technology, through high-speed WIFI transmission, through the smart phone APP on the phone and the computer displays the various parameters, and data can be excel, jpg and other formats output.
In other words, compared with the light quantum meter, SPIC-200 wavelength measurement range is wider, higher accuracy, better applicability of plant measurement, can be widely used in plant plants, soilless cultivation, greenhouse and other plant growth in the light Radiation on-site monitoring.
The performance evaluation of LED plant lighting products involves multiple metering systems with more evaluation parameters and narrow spectrum, both for test hardware and software, such as optical radiation detector matching problems and spectral measurements Accuracy and so on.
LED plant lighting manufacturers and related scientific research institutions should be based on their own or standard requirements, based on the impact of light on the plant, select the appropriate measurement program, a comprehensive and objective evaluation of LED plant lighting products of the performance, and then design plant growth lighting system Or fill light program, so that green lighting, efficient lighting.