Watts-level ultraviolet-CLED integrated light sources for efficient surface and air sterilization

With the epidemic of the coronavirus disease(COVID-19) infection, AlGaN-based ultraviolet-C light emitting diodes(UVC-LEDs) have attracted widespread attention for their sterilization application. However, the sterilization characters of high power integrated light sources(ILSs) haven’t been widely investigated before utilizing in public sanitary security. In this work,by integrating up to 195 UVC-LED chips, high power UVC-LED ILSs with a light output power(LOP) of 1.88 W were demonstrated. The UVC-LED ILSs were verified to have efficient and rapid sterilization capability, which have achieved more than99.9% inactivation rate of several common pathogenic microorganisms within 1 s. In addition, the corresponding air sterilization module based on them was also demonstrated to kill more than 97% of Staphylococcus albus in the air of 20 m3 confined room within 30 min. This work demonstrates excellent sterilization ability of UVC-LED ILSs with high LOP, revealing great potential of UVC-LEDs in sterilization applications in the future.

Evaluation and Enhanced Use of Light Emitting Diodes for Hydroponics

Hydroponic farming is a viable and economical farming method,which can produce safe and healthy greens and vegetables conveniently and at a relatively low cost.It is essential to provide supplemental lighting for crops grown in greenhouses to meet the daily light requirement,Daily Light Integral(DLI).The present paper investigates how effectively and efficiently LEDs can be used as a light source in hydroponics.It is important for a hydroponic grower to assess the requirement of photo synthetically active radiation(PAR)or the Photosynthetic Photon Flux Density(PPFD),in a greenhouse,and adjust the quality and quantity of supplemental lighting accordingly.A Quantum sensor(or PAR sensor)can measure PAR more accurately than a digital light meter,which measures the light intensity or illuminance in the SI unit Lux,but a PAR sensor is relatively expensive and normally not affordable by an ordinary farmer.Therefore,based on the present investigation and experimental results,a very simple way to convert light intensity measured with a Lux meter into PAR is proposed,using a simple conversion factor(41.75 according to the present work).This allows a small-scale hydroponic farmer to use a simple and inexpensive technique to assess the day to day DLI values of PAR in a greenhouse accurately using just an inexpensive light meter.The present paper also proposes a more efficient way of using LED light panels in a hydroponic system.By moving the LED light panels closer to the crop,LED light source can use a fewer number of LEDs to produce the same required daily light requirement and can increase the efficiency of the power usage to more than 80%.Specifically,the present work has determined that it is important to design more efficient vertically movable LED light panels with capabilities of switching individual LEDs on and off,for the use in greenhouses.This allows a user to control the number of LEDs that can be lit at a particular time,as required.By doing so it is possible to increase the efficiency of a LED lighting system by reducing its cost of the electricity usage.

Effects of environment lighting on the growth,photosynthesis,and quality of hydroponic lettuce in a plant factory

Leafy vegetable production under controlled environment using artificial lighting has many advantages over conventional greenhouses and open-field production.However,high initial investment and operation costs are restricting the wide application of this technology.In order to design an optimal artificial lighting environment for lettuce production,effects of different combinations of light intensity,photoperiod,and light quality on growth,quality,photosynthesis,and energy use efficiency of lettuce(Lactuca sativa L.cv Ziwei)were investigated under a closed plant factory.Lettuce transplants were grown under photosynthetic photon flux density(PPFD)at 150μmol/m^(2)·s,200μmol/m^(2)·s,250μmol/m^(2)·s,and 300μmol/m^(2)·s provided by fluorescent lamps(FL)with a red to blue ratio(R:B ratio)of 1.8 and light-emitting diode(LED)lamps with R:B ratio of 1.2 and 2.2,in combination with photoperiod of 12 and 16 h/d.In order to examine the“long term”photosynthetic characteristics,net photosynthetic rates of hydroponic lettuce leaves were continuously measured for 2 d(15^(th) and 16^(th) day after transplanting)before harvest.There was no difference in leaf fresh weight(FW)between PPFD of 250μmol/m^(2)·s and 300μmol/m^(2)·s with photoperiod of 16 h/d,regardless of light quality,and same results showed in contents of nitrate,soluble sugar,and vitamin C,respectively.The results of continuous measurements of net photosynthetic rate of lettuce leaves before harvest indicated that plants grown at PPFD of 250μmol/m^(2)·s had consistently higher compared to those grown at PPFD of 300μmol/m^(2)·s.Combining the results from growth,photosynthesis,quality,and energy consumption,it can be concluded that PPFD at 250μmol/m^(2)·s with photoperiod of 16 h/d under LED with R:B ratio of 2.2 is a suitable light environment for maximum growth and high quality of commercial lettuce(cv.Ziwei)production under indoor controlled environment.

Effects of light intensity and photoperiod on runner plant propagation of hydroponic strawberry transplants under LED lighting

Vegetative propagation of strawberry(Fragaria×ananassa Duch.)in the plant factory with artificial lighting is considered as an effective approach to produce high-quality transplants.In this study,mother plants of‘Benihoppe’strawberry were grown hydroponically for 50 d under eight LED lighting treatments by combining four levels of light intensity(200,250,300 and 350mmol/(m^(2)·s))and two photoperiods(12 h/d and 16 h/d).Runner development,growth of runner plants,photon yield and energy yield in runners and runner plants were investigated to evaluate the strawberry propagation efficiency.Results indicated that length of runners decreased linearly with increasing daily light integral(DLI)under each photoperiod and was significantly shorter under photoperiod of 16 h/d.Runner elongation was inhibited by high DLI.Number of runners and runner plants formed by mother plants increased by 38.9%and 33.7%,when DLI increased from 8.6 to 11.5 mol/(m^(2)·d),respectively;however,no further increase was observed when DLI was higher than 11.5 mol/(m^(2)·d).Similar trends were found in crown diameter and biomass of primary and secondary runner plants.Negative impact of high DLI(20.2 mol/(m^(2)·d))on photosynthetic capacity of runner plants was observed as a decrease in leaf net photosynthetic rate,potential maximum photochemical efficiency of PSII,and chlorophyll content.Furthermore,photon yield and energy yield in runners and runner plants decreased significantly with increasing DLI.Therefore,DLI in a range of 11.5-17.3 mol/(m^(2)·d)is beneficial to improve strawberry propagation efficiency and quality of runner plants,and 11.5 mol/(m^(2)·d)is optimal for the strawberry propagation of runner plants in the LED plant factory because of the higher photon and energy yields.

LED supplementary strategy based on hourly light integral for improving the yield and quality of greenhouse strawberries

Supplemental lighting is critical to the growth of greenhouse crops under the environmental conditions of low temperatures combined with weak radiation during the winter and spring seasons.To achieve the essential daily light integral(DLI)for greenhouse crop growth,a supplemental light strategy was proposed based on hourly light integral(HLI).The target HLI was calculated by dividing the target DLI by the duration of light exposure,while the actual HLI was obtained by accumulating the Photosynthetic Photon Flux Density(PPFD)based on real-time monitoring.Subsequently,the supplemental lighting duration for the next hour was determined by the difference between the target HLI and the actual HLI from all previous periods.Furthermore,the supplementary lighting strategy incorporated maximum values for both PPFD and temperature,and the supplemental light was withheld whenever the actual PPFD or temperature exceeded these values.An experiment was conducted on strawberries in a commercial greenhouse,targeting a DLI of 12.6 mol/(m2∙d),with no supplemental lighting as the control.The results indicated that LED supplemental lighting based on HLI increased the DLI to approximately10 mol/(m2∙d)and raised the strawberry canopy temperature by 1°C-2°C.Compared to the control treatment,the LED supplemental lighting based on HLI significantly improved the net photosynthetic rate,stem thickness,number of leaves,leaf length,and leaf width of the strawberry plants.Additionally,the fruit yield per plant,soluble solids content,and sugar-acid ratio in the supplemental lighting treatment increased by 32%,21%,and 33%,respectively.Thus,LED supplemental lighting based on HLI is an effective strategy for improving the yield and quality of greenhouse crop production.

Growth of cucumber seedlings in different varieties as affected by light environment

High-quality cucumber seedlings are a prerequisite for ensuring high yield of cucumbers.With the continuous increase of cucumber planting area in China,the demand for high-quality cucumber seedlings is also increasing.One of the important ways to improve the quality of cucumber seedlings is to improve the light environment by using artificial light source.In this study,three cucumber seedlings(cv.Jintong,cv.Yunv and cv.Xiazhiguang)were grown for 23 d under eight levels of daily light integral(DLI)at 4.3 mol/(m^(2)·d),8.6 mol/(m^(2)·d),10.1 mol/(m^(2)·d),13.0 mol/(m^(2)·d),5.8 mol/(m^(2)·d),11.5 mol/(m^(2)·d),14.4 mol/(m^(2)·d)and 17.3 mol/(m^(2)·d),respectively.The results showed that when DLI was 14.4 mol/(m^(2)·d),the seedling height,stem diameter,total leaf area and shoot dry/fresh weight of all three cucumber cultivars reached the maximum,while hypocotyl length decreased with the increase of light intensity.When DLI was 14.4 mol/(m^(2)·d),Jintong and Xiazhiguang had the highest health index,which were 49.29 and 28.56,respectively,while that of Yunv was 81.59(DLI=14.4 mol/(m^(2)·d)).With the increase of DLI,the photosynthetic capacity of cucumber increases gradually.The highest net photosynthetic rate was shown at DLI of 14.4 mol/(m^(2)·d),while the chlorophyll content of cucumber seedlings of all three cultivars were less affected by DLI.Jintong and Yunv had the highest chlorophyll content when DLI was 8.6 mol/(m^(2)·d)because they were adapted to low-light environment.In conclusion,the DLI of 14.4 mol/(m^(2)·d)for Jintong and Xiazhiguang,while that of 17.3 mol/(m^(2)·d)for Yunv are suggested for the light environment design of factory-cultivated seedling for cucumber.

Agricultural Load Modeling Based on Crop Evapotranspiration and Light Integration for Economic Operation of Greenhouse Power Systems

The threat of environmental degradation attracts great attention to clean energy production and transportation.However,the limited scope of energy consumption causes the large-scale of clean energy sources to be abandoned in Sichuan province.In the meantime,the development of modern greenhouse cultivation has transformed the agriculture industry to develop a brand-new type of electrical load in the grid.Consequently,the agricultural load can be used to consume the clean energy while facilitating plant growth.In this paper,an innovative agricultural load model is proposed based on crop evapotranspiration and daily light integration.Furthermore,the proposed agricultural load model is also applied to investigate the electricity consumption of five types of crop planting.The results illustrate that the power consumption is primarily driven by an artificial lighting compensation system.

Advances in the light field displays based on integral imaging and holographic techniques(Invited Paper)

Light field displays comprise three-dimensional （3D） visual information presentation devices capable of providing realistic and full parallax autostereoscopic images. In this letter, the recent advances in the light field displays based on integral imaging （II） and holographic techniques are presented. Several advanced approaches to demonstrate the light field displays including viewing angle enhancement techniques of the II display, a fast hologram generation method using graphics processing unit （GPU） and multiple WRPs, and a holographic microscopy to display the living cells are reported. These methods improve some important constraints of the light field displays and add new features.