Measurement And Regulation Of Plant Lighting Parameters Under Photonic Photometry

There are more than 50 percent of the world's population living in cities since 2007,and the proportion of China's urban population has exceeded 60 percent in 2019.The urban agriculture,such as artificial lighting plant factories(PFAL),was activated because of large and rapidly growing urban population's demand for nearby supply of vegetables.Through the integration of optoelectronics,automation,modern agriculture etc,PFAL has achieved a high-density cultivation and annual continuous cropping in a limited space.The annual vegetable production per unit area in PFAL can easily reach more than 100 times than the open fields.The rapid development of LED-based plant lighting technology has made it possible to use PFAL on a large scale,which is expected to completely solve the food crisis of mankind.However,even though the quality of the vegetables is better,the power consumption of LEDs in PFAL cause the price double than the outdoor production under free sunlight.How to reduce the energy consumption of lighting in PFAL is the key to the future fate and applicability of this technology.The article explores the challenges from the viewpoint of optical engineering which aimming to explore the ways for energy consumption reducing.Five aspects are focused on,including the establishment of the standard evaluation system for plant lighting,development of multichannel photon flux density sensor(MPS),establishment of a standard light formula screening platform,and the feasibility of improving the efficiency of light energy utilization with light frequency.The main research results are as follows:1.The misunderstanding about plant lighting measurement system and unclear evaluation criteria hinder the progress of plant lighting.Thus,the mathematical expressions of flux and intensity of four optical measurement systems,including radiology,photometry,photonic photometry and plant photonic photometry,were systematically derived in this paper.The standard plant lighting evaluation software(PLES),which is based on photonic photometry,is developed creatively.It uses the general light source measuring instruments such as distributed photometer or integrating sphere to realize the transformation of measurement system.The PLES calculates lighting's photon flux efficiency(PFE),photon flux density(PPF),light quality ratio(R/B),photon spectroscopy,and other important parameters which realized the standardization and parallel comparison of different kinds of plant lighting sources with different spectra.2.Aiming at the problem that the key lighting parameters such as PPFD and R/B can not be measured synchronously in plant lighting application scenarios such as PFAL and lighting supplement in greenhouse,an MPS sensor was designed to realize a low-cost and synchronous measurement of BPFD,RPFD and PPFD.In this article,the development of the hardware,software and structure of the MPS sensor is discussed.The mathematical relationship between the calibration coefficients of different channels is established.The calibration of three channels of the sensor is realized by using a standard PAR sensor.The optical crosstalk between BPFD and RPFD channels is reduced by 86%leveraging the 3D-printed anti-crosstalk sleeve.The calibration results show that the linear response variances of the three channels were all above 0.999.Accordingly to the actual needs of plant lighting,the sensor fills the gap between the spectrometer and PAR sensor at home and abroad,so that plant lighting has the ability to realize the simultaneous real-time control of light intensity and spectrum.3.In view of the fact that the existing optimal light formula experimental platform does not achieve accurate control of plant lighting parameters,the artical demonstrates a breakthrough in simultaneous measurement and closed-loop control of RPFD,BPFD,PPFD and R/B.It is realized by developing a control system based on FPGA and designing a multi-channel LED light source.In addition,other environmental parameters,such as temperature,relative humidity,CO2 concentration and photoperiod also were accurately controlled at control accuracy with±0.3?,±5%,±50 ppm and 1s respectively.The control errors of RPFD,BPFD and PPFD are 1.43%,1.39%and 0.71%respectively after 30s of parameter setting.In addition and based on this platform,a laboratory special spectrum adjustable artificial climate chamber and a set of greenhouse light supplement systems based on daily light integral(DLI)control have been developed.4.Aiming at the problem that the PFAL does not realize the maximization of light energy utilization efficiency through the optimal light formula,we adopted the spectral adjustable artificial climate chamber,and taking tea seedlings as the research material to explore the optimal light formula for cultivating those tea seedlings with artificial light.It was found that blue light could improve the quality index of new bud leaves,increase the content of free amino acids and tea polyphenols,and decrease the phenol-ammonia ratio(P/A).Red light can promote the biomass accumulation of tea shoots and leaves,but when the proportion of red light is high,the P/A value of tea shoots is higher,which means the tea shoots have a lower quality.R/B=1/3 can improve the quality of tea leaves on the premise of ensuring the biomass of new buds and leaves of tea seedlings.This is an ideal R/B parameter for artificial light cultivation of tea seedlings.When PPFD=100 ?mol·m-2·s-1,the new bud leaves of tea seedlings had the best quality showing a high amino acid content,a relatively low tea polyphenols content,low P/A,and high biomass index.In conclusion,PPFD=100 ?mol·m-2·s-1 and R/B=1/3 are the optimal light formula for tea seedling cultivation with artificial light source.This experiment provides a general technical route and reference for the selection of optimal light formula in plant factories.5.According to the characteristics of LED being able to achieve high frequency adjustment,we were inspired by the human eye visual enhancement effect of flashing light.Through the adoption of MPS and red blue dual channel LED light sources,designed to achieve frequency(F)and duty ratio(R)and resulting in an average PPFD,a lighting model of multiple parameters such as flashing light biological experiment platform was realized,which come ture a maximum 1 MHz flashing frequency modulation,a 0?100%duty ratio control range,and four kinds of innovation in digital lighting mode.In addition,the platform was also used to test the growth rate(OD750)of a model crop Chlamydella Rheinense.By setting six treatments between 0 and 10 KHz,it was found that under 1 KHz pulsed light,the growth rate of microalgae was significantly better than that of continuous light and had the highest maximum light use efficiency(Fv/Fm)of PS(?).The results provide guidance for us to use flashing light to improve the efficiency of light energy utilization in plant factory.