LED as light source for baby leaves production in an environmental controlled chamber

Transcription

1 Proceedings of the 4 th International Symposium on Machinery and Mechatronics for Agriculture and Biosystems Engineering (ISMAB) May 2008, Taichung, Taiwan LED as light source for baby leaves production in an environmental controlled chamber Wei Fang 1*, Chia-Chyi Wu 2, and Ming-Yih Chang 2 1 National Taiwan University, Taiwan, R.O.C. 2 Ilan University, Taiwan, R.O.C. *Corresponding Author, weifang@ntu.edu.tw Abstract: Using Light-Emitting Diodes (LED) as light source for plant production was started in 1980s for mission to Mars by NASA, USA. Later, the technology spread worldwide and has been used to grow various crops in lab scale for young plants required low light such as tissue culture plantlets, seedlings, etc. Only until recently, the technology of high power (HP) LED (1, 3, 5, 10, 30, 50 W and higher) become mature, the efficacy of HPLED reaches the level of tubular florescent lamp and beyond. Furthermore, the costs of HPLED drop dramatically, thus making it more applicable for mass production. This paper introduced a baby leaves production system in a controlled environment chamber using high power RGB composed white LEDs as light source. The design enables multi-shelf production, thus maximizing productivity per unit floor area. Such crop producing system does not need any pesticides and level of nitrate in leaves can be controlled, CO 2 can be better used. Time to harvest, amount of harvest per floor area can be predicted. Light quality was found critical not only to the dry matter, but also color, degree of crispy (tenderness), degree of bitterness (taste), soluble solid, chlorophyll, vitamin C, and nitrate contents of baby leaves. Key Words: high power LED, baby leaves, CEA INTRODUCTION Due to weather constraint, head/semi-head lettuce (Lactuca sativa L.) can be produced only from October/September to February/March in the open fields of the plain area of Taiwan. Totally, 11,388 tons, 5,339,000 US$ worth, of lettuce was imported in Among lettuce imported, head and semi-head lettuce occupied % in weights and 50.2 % in value, leaf lettuce although in less quantity, but in much higher price. Using Light-Emitting Diodes (LED) as light source for plant production was started in US for space research in 1980s. After the invention of blue LED in 1994 and 10 years after, the light intensity of red and blue LEDs was still too weak for vegetable production and was used for seedling and/or tissue culture plantlets production only. The costs remain too high for commercial growers. Until recently, the technology of high power (HP) LED (1, 3, 5, 10, 30, 50 W and higher) become mature, the efficacy of HPLED reaches the level of tubular florescent lamp (> 60 lm/w) and beyond (> 100 lm/w). Furthermore, the costs of HPLED drop dramatically, thus making it more applicable ET-7 The authors are solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of Chinese Institute of Agricultural Machinery, Taiwan (CIAM), and its printing and distribution does not constitute an endorsement of views which may be expressed. Technical presentations are not subject to the formal peer review process by CIAM editorial committees; therefore, they are not to be presented as refereed publications. Citation of this work should state that it is from the 4 th ISMAB paper. EXAMPLE: Author's Last Name, Initials Title of Presentation. The 4 th ISMAB May 27-29, Taichung, Taiwan. For information about securing permission to reprint or reproduce a technical presentation, please contact CIAM at mailto:choucy@ntu.edu.tw or Chinese Institute of Agricultural Machinery, 136 Chou-Shan Rd., Taipei 106, Taiwan.

2 for mass production of vegetables such as lettuce. LEDs can be hanged vertically or placed on top of the canopy. Massa, et al. (2006) grown cowpea, a planophile dry bean crop, using vertically hanged intracanopy LED lights, more biomass is produced, a higher index of biomass per kwhr is obtained and the oldest leaves are retained throughout stand development than when overhead LEDs are used. Red light along can find its application in the growth of Zantedeschia plantlets in vitro and tuber formation (Jao et al., 2005). The combination of red and blue LED light was an effective light source for several crops (Jao and Fang, 2003). Yet the appearance of plants under red and blue lighting is purplish gray making visual assessment of any problems difficult. The addition of green light would make the plant leave appear green and normal similar to a natural setting under white light (Kim et al., 2004). Effects of intermittent light on the photomixtrophic growth of potato plantlets in vitro and the possibility of electricity savings by adjusting the frequency and duty ratio of light-emitting diodes (LEDs) were investigated and a driver capable of adjusting light intensity, quality, frequency and duty ratio was developed by Jao and Fang (2003, 2004a). Further investigation was conducted by the same researchers to test the concurrent versus alternating red and blue light photoperiods (Jao and Fang, 2004b). The objective of this study was to investigate on the effects of light quality and quantity on the growth and metabolites of lettuce using HP LEDs as light source. MATERIALS AND METHODS Lettuce seeds were spread on rockwool, growth in controlled chamber at 22/18 degree C day/night temperature with 12/12 hours light/dark cycle for 2 weeks. Seedlings were then grown hydoponically (floating board method) in a controlled room with day/night temperature controlled at 25/20 degree C and light/dark cycle of 20/4 hours for 14 days. Four types of lettuce (leafy Red Rapid, leafy Grand Rapid, semi-head Butter head, head Romaine ) and 3 types of commercially available fertilizer (Hyponex #1 (7-6-19), #2 ( ), #4 ( )) diluted 1000 times were used. Each treatment has 3 trays and 6 plants per tray. Upon harvest in fertilizer experiment, shoot fresh weight and dry weight, root fresh weight, vitamin C and nitrate content (Spectrometer, Merck RQ flex), chlorophyll content (Minolta SPAD-502), and soluble carbohydrate content (Moris, 1948) were measured. For other experiments, dry weight measurement was excluded and sensory evaluation of color, taste of bitterness, and tenderness on harvested lettuce was conducted. Each analysis has 15 replicates. Portable spectroradiometer (LI-1800, LICOR, USA) was used in measuring light spectrum and PAR (Photosynthetically Active Radiation, in umol/m 2 /s) of LEDs and Tubular florescent lamps (T12 and T5). Two levels of PAR (100 and 300 umol/m2/s) with different combinations of R/G/B intensity (termed light quality) were tested. Two generations of LED light panels were developed with help from Everlight Electronics Co. LTD. First generation LED lighting system for each shelf consists of heat dissipation fans and square light panels connected in both longitudinal and lateral directions. Each light panel has 6 red (peak wavelength@640 nm), 6 blue (465 nm) and 6 green (525 nm) LED bulbs (1 W each) arranged to achieve greatest uniformity as shown in Figure 1. Heat generated was dissipated through fans mounted at the back of LEDs. The combination of LED lamps and fans make the entire lighting system heavy and bulky. Figure 2 shows the 2 nd generation of LED panel with 4 rows of LED light bars mounted on a metal (stainless steel) sheet at the size of the floor area of the cultural bench. Each row consists of 4 light ET-8

3 bars with 10 RGB (peak 525 and 465 nm, respectively) high power (HP) LEDs (3 W each) per bar. Totally, 40 pieces of HP LEDs per row and 160 pieces per panel. The power supply (Mean Well, SP , Taiwan) provides up to 31.3A at 24 V (750 W). Figure 3 shows blue light on in the dark of a 2 nd generation LED panel. Figure 4 shows the controller and display. Figures 5 and 6 show P (pulse) and D (duty) mode of the controller, respectively. Controller allows users to adjust frequency (92 ~ Hz) and duty ratio (0~100 %) of R, G, B light separately by pressing buttons shown in the lower right corner of the Figure 4. Fig. 1. The 1 st general LED light panel Fig. 2. The 2 nd general LED light panel Fig. 3. The 2 nd generation LED light panel with blue light on in the dark. Fig. 4. Control panel and display Fig. 5. The display shows Pulse mode Fig. 6. The display shows Duty mode RESULTS AND DISCUSSION The 1 st generation light panel Unit conversion between photometric and quantum units of 645, 525 and 465 nm RGB LEDs used in 1 st generation LED light panel are 32.65, and lux per umol/m 2 /s, respectively. Based on the values derived in this study, RGB LEDs at lux equals , and umol/m 2 /s; in contrast, 100 umol/m 2 /s equals 3265, 9848 and 1962 lux, respectively. The 2 nd generation light panel and controller Figures 5 shows contour lines of the PAR (in umol/m 2 /s) of red LEDs at 100 % duty ratio, 100 Hz. Distance from light panel to sensor is fixed at 25 cm. Totally, 5 x 12 points were measured per color of light with each point 10 cm apart. The peak of the contour lines are 180, 80 and 125 umol/m 2 /s for red, ET-9

4 green and blue LEDs, respectively. The uniformity can be improved by adding some reflectors at 4 sides. Figure 6 shows linear relationship between PAR and duty ratio. Electric current vs. duty ratio is linear relationship as well. Fig. 5. Contour lines of PAR on bench PAR ( mol/m 2 /s) Red LED Duty Ratio (%) Fig. 6. PAR vs. duty ratio Effect of fertilizer on lettuce production Table 1 shows effect of fertilizer on the growth and metabolite of leafy lettuce Red Rapid in greenhouse under natural light condition. Plants growth with Hyponex #1 has the greatest fresh weight and lowest nitrate content. Hyponex #1 was used in later experiments there after. Table 1. Effect of fertilizer on the growth and metabolite of leafy lettuce Red Rapid Treatment Shoot Root Shoot dry Chlorophyll Soluble Vitamin C Nitrate fresh wt. fresh wt. wt. (g) content carbohydrat content content (g) (g) (SPAD e ontent (ppm) (ppm) unit) (ppm) Hyponex#1 73.1a 7.2a 4.0a 16.8b 565.0a 1472b 1690b (7-6-19) Hyponex#2 26.5b 5.2ab 1.5b 25.0a 533.5a 1440b 1754b ( ) Hyponex#4 ( ) 15.0c 2.4c 0.9c 21.9a 533.5a 1810a 1994a Multiple Range Test. Effect of light quality on lettuce production Table 2 shows effect of various light quality (same total PAR of 100 umol/m 2 /s using 1 st generation light panel) on the growth and metabolites of leafy lettuce Grand Rapid. RGB LEDs at 3 combinations were tested and tubular florescent lamp (T12) was used as control group. Treatment with RGB in equal photons (R33/G33/B33) grows poorly due to lack of red light. However, this treatment also grows lettuce with highest soluble solid ( o Brix), vitamin C content and lowest nitrate content. 10 % green light (R80/G10/B10) enhances growth of leafy lettuce compare with R90/B10 treatment in shoot fresh weight. Table 2. Effect of various light qualities on the growth and metabolites of leafy lettuce Grand Rapid Light Shoot fresh Root fresh Vitmin C Nitrate treatment wt. (g) wt. (g) content (ppm) content (ppm) Chlorophyll content (SPAD unit) ET-10 soluble solid ( Brix) R90/G0/B b 2.4bc 16.7a 0.45b 1182ab 2140a R80/G10/B a 4.4a 13.4b 0.37bc 1067bc 2148a R33/G33/B33 4.6c 1.9c 13.2b 0.85a 1328a 253b T a 3.2b 13.4b 0.42b 1198ab 2195a Multiple Range Test

5 Table 3 shows results of sensory evaluation conducted for leafy lettuce Grand Rapid produced under various light quality. Among groups of high portion (80, 90 %) of red light, 10 % of green enhance tenderness and reduce bitterness. Treatment of equal portion of RGB light performs poorly in all aspects. Table 3. Effect of various light quality on the sensory evaluation of leafy lettuce Grand Rapid Light treatment Color Tenderness Bitterness (taste) R90/G0/B R80/G10/B R33/G33/B T Score of 5 with 1 the worst. Effect of light quantity on lettuce production Table 4 shows effect of various light quantities and quality on the growth and metabolites of butter head lettuce. Treatment of R240/G30/B30 (300 umol/m2/s, provided by 2 nd generation light panel) can produce lettuce (23 g) with almost two times in fresh weight compare with R90/B10 (13.6 g) and T12 (14.1 g) treatments in 14 days. One unique finding was that T5 lamps provided with PAR at 280 performed poorly compare with T12 lamps at 100 umol/m2/s. Last row of Table 4 shows the shoot fresh weight of lettuce grown in greenhouse during same period of time (Winter of 2007), is only 1/15 of the same crop grown under R240/G30/B30 LED in controlled environment. This fact reveals the potential for plant production using LEDs in an totally controlled environment. Table 4. Effect of various light quality and quantities on the growth and metabolites of butter head lettuce Light treatment Shoot Root fresh Chlorophyll soluble Vitamin C Nitrate fresh wt. wt. (g) (g) content (SPAD unit) solid ( Brix) content (ppm) content (ppm) R90/G0/B b 1.7bc 24.9c 3.8bc 1340b 2068ab R80/G10/B10 8.8c 0.9c 28.2b 6.5a 1762a 1986ab R240/G30/B a 5.4a 38.0a 4.0b 1262ab 1610bc T b 1.5bc 23.8c 3.6bc 1578ab 2274a T5(280μmol/m 2 /s) 12.1bc 2.4b 25.9bc 2.4c 1366b 1838ab Sunlight (winter) 1.5d 0.5c 17.8d 3.2bc 1382b 1234c Multiple Range Test Table 5. Effect of various light quality on the growth and metabolites of Romaine lettuce light Shoot fresh Root fresh Chlorophyll Soluble Vitamin C treatment wt. (g) wt. (g) content (SPAD unit) solid ( Brix) content (ppm) Nitrate content (ppm) R90/G0/B10 1.2b 0.2ab 45.0a 0.2a 2546ab 1778bc R80/G10/B10 1.8a 0.4ab 44.8a 0.3a 2928a 1884ab R33/G33/B33 2.4a 0.2ab 38.7ab 0.2a 2918a 2346a T12 1.6ab 0.6a 41.0a 0.2a 2708a 1936ab Multiple Range Test ET-11

6 CONCLUSIONS Two generation of light panels were developed capable of providing flexible and stable control functions. Frequency and duty ratio of R/G/B LED light can be adjusted in the range of 92 to Hz and 0 to 100 % separately. Duty ratio has direct proportion to PAR quantity and electricity consumption. The method of heat dissipation for LED panel was simplified thus reducing the weight and thickness of the light panel. For leafy lettuce Grand Rapid, high proportion (80 and 90 %) of red light promotes growth. Treatment of R80/G10 is better than R90/G0 indicates the beneficial effect of the coexistence of the green light. Green light enhance not only in dry matter accumulation but also in tenderness and bitterness reduction. However, benefits from high proportion of red light may not be true for head lettuce Romaine, which increases its fresh weight and nitrate content with respect to the increase of green light portion under same total PAR. Compare with greenhouse production at poor weather condition, production of semi-head lettuce (butter head) provided with 300 umol/m2/s in controlled chamber can be 15 times better in shoot fresh weight indicates the potential of totally controlled plant production. With CO 2 enrichment (1200 ppm for example), and in multi-shelf (10 layers for example), the production per unit floor area can be more than 100 times and the time to harvest can be further reduced. ACKNOLEDGEMENTS Authors would like to express our sincere thanks to Everlight Electronic Co. LTD. for the support of research fund and for the help in the construction of LED light panels used in this study. REFERENCES Jao, R.C. and W. Fang An adjustable light source for photo-phyto related research and young plant production. Applied Engineering in Agriculture, Vol. 19(5): Jao, R. C. and W. Fang. 2004a. Effects of frequency and duty ratio on the growth of potato plantlets in vitro using LEDs. HortScience. 39(2): Jao, R. C. and W. Fang. 2004b. Growth of potato plantlets in vitro is different when provided concurrent versus alternating red and blue light photoperiods. HortScience, 39(2): Jao, R. C., C.C. Lai, W. Fang and S.F. Chang Effects of Red light on the Growth of Zantedeschia Plantlets in vitro and Tuber Formation Using Light-emitting Diodes. HortScience, 40(2): Kim, H. H., G. D. Goins, R. M. Wheeler and J. C. Sager Green-light Supplementation for Enhanced Lettuce Growth under Red- and Blue-light-emitting Diodes. HortScience 39(4): Moris, D. L Quantitative determination of carbohydrates with Dreywood s anthrone reagent. Science 107: Massa, G. D., Jeffery C. Emmerich, R. C. Morrow, C. M. Bourget and C. A. Mitchell Reconfigurable LED Lighting System Development: Potential Energy Savings for CEA. HortScience 41: ET-12