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.
Absorption spectra of chlorophyll a and chlorophyll b (cited from CIE 2012)
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 and 700 nm.
Again, the light is uniform. 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, I am long. 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, photoquantometry 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 mismatching problems, 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 measurement equipment. The remote hand-held SPIC-200 spectral color illuminometer can solve the above problems.
The SPIC-200 illuminometer solves the spectral mismatch problem of traditional illuminance meter and colorimeter, realizes zero mismatch, and adopts the international patented SBCT (Split-Integration Combination) technology to greatly expand the photometric range and improve the accuracy. The method combines the integration method and the spectroscopy method to improve the linearity of the spectral measurement by accurately correcting the absolute value of the spectral measurement to obtain accurate performance parameters of the LED plant illumination product, and is the world's most recognized luminosity/radiation measurement with the highest precision. method. The illuminance accuracy is guaranteed to be within 4%, and the actual illuminance measurement range is extended to 0.1lx~200klx, and the lowest measurable 0.1lx, f1'≈0, which is the highest level of similar instruments in the world today.
In addition, the patented complex variable matrix stray light correction technology improves the stray light control ability in the spectrum measurement by 1~2 orders of magnitude, and the stray light effect is ≤0.3%.
Main Specifications:
Wavelength range: 380nm ~ 760nm
Wavelength accuracy: ±0.5nm
Illuminance measurement range: 0.1lx ~ 200klx
Illumination accuracy: ± 4% (reading +1 words)
Stray light: ≤0.3%
Chromatographic coordinate accuracy: ±0.001 (compared to standard light source with traceability to NIM better than ±0.0001)
Through the corresponding head and spatial analysis cosine, the conversion between multiple systems can be easily realized, and the relative spectral power distribution, photosynthetic irradiance, optical quantum density, chromaticity coordinates, illumination uniformity, peak wavelength, and Main wavelength, radiance ratio, color temperature, color rendering index and other parameters.
Can measure general parameters:
1) Relative spectral power distribution P(λ)
2) Spectral irradiance E(λ)
3) chromaticity 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 (MacAdam ellipse, rectangular box and CIE u'v' circle)
7) Peak wavelength, half width
8) Color purity, dominant wavelength
9) Red ratio
10) Illuminance E, irradiance Ee
11) More measurement functions can be customized
Measure plant lighting parameters:
For on-site measurement with high precision requirements, a measuring instrument with small size and fast measuring speed is needed, so that it can be carried and read data at any time. The SPIC-200 has a 4.2-inch touch screen, exquisite design, and a very mobile phone grip. One-button operation, one-step on-site measurement and analysis, truly can be called real-time data reading, millisecond precision measurement. Built-in high-capacity SD mobile memory card, intelligent operating system and other modern technologies, through high-speed WIFI transmission, you can display various parameters on the mobile phone and on the computer through the smart phone APP, and the data can be output through various formats such as excel, jpg and so on.
That is to say, compared with the optical quantum measuring instrument, the SPIC-200 has a wider measurement range and higher measurement accuracy, and has wider applicability for plant measurement, and can be widely applied to plant growth in plant factories, soilless culture, greenhouses, and the like. On-site monitoring of radiation.
summary
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.
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