Greenhouse Roberto G. Lopez Department of Horticulture Michigan State University The term daily light integral (DLI) describes this cumulative amount of light (photons of light) that an area or location receives during one day. Quantity of Light DLI is the cumulative amount of photosynthetic light received in 1 square meter of area (10.8 sq. ft.) each day, or mol m 2 d 1. Daily Light Integral (DLI) DLI cannot be determined from an instantaneous reading DLI is similar to a rain gauge A rain gauge is used to measure the total amount of rain that was received in a particular area during a 24-hour period Daily Light Integral (DLI) Values from sunlight outdoors vary from 5 (winter in the North) to 60 mol m-2 d-1 (in the Southwest in summer) In a greenhouse, values seldom exceed 30 mol m -2 d-1 because of shading and structures which can reduce light by 40 to 70% Target DLI of 10 to 12 mol m-2 d-1 Greenhouse Grower Challenges: Light Intensity Propagators of young plants are interested in: 1) Minimizing production time for seedlings (plugs) and rooting of cuttings (liners) to reduce energy costs Daily Light Integral (DLI) and Young Plants Avg. Greenhouse DLI (mol m -2 d -1 ) Benefit of 7 Large 9 Moderate 11 Small February 2) Optimizing quality of young and finished plants The production environment and culture impacts crop quality and timing Korczynski et al., 2002 February Runkle, 2011 Not for publication 1
Plant Responses to Increased DLI Leaves (smaller and thicker) Time to flower (faster, due partly to temperature) Branching (increased) Stem diameter (increased) Plant height (sometimes reduced) Root growth (increased) Low DLI High DLI New Guinea impatiens Harmony White Photo taken after 16 d of propagation 1.3 2.1 4.0 5.7 Sunlight DLI (mol m -2 d -1 ): 6.3 10.8 Sunlight + HPS Root dry mass (mg) 8.0 14.5 30.0 35.5 48.5 55.5 Argyranthemum Madiera Cherry Red Photo taken after 21 d of propagation DLI (mol m -2 d-1 ): 1.4 2.0 3.8 5.6 6.4 7.2 10.6 12.3 Sunlight Sunlight + HPS Root dry mass (mg) 14.9 22.6 27.1 48.0 40.1 45.6 56.0 84.0 Shoot dry mass (mg) Shoot dry mass increases with DLI 300 250 200 150 100 50 0 Argyranthemum, R 2 = 0.45 *** Angelonia, R 2 = 0.42 *** DLI (mol m -2 d 0 2 4 6 8-1 ) 10 12 14 Daily light integral (mol m -2 d-1 ) 3.5 3.0 Stem caliper increases with DLI Argyranthemum, R 2 = 0.51*** Angelonia, R 2 = 0.31 *** Root biomass increases with DLI 80 Angelonia, R 2 = 0.70 *** Argyranthemum, r 2 = 0.70 *** Diascia, r 2 = 0.65 *** Stem caliper (mm) 2.5 2.0 Root dry mass (mg) 60 40 1.5 20 1.0 0 2 4 6 8 10 12 14 Daily light integral (mol m -2 d -1 ) 2 4 6 8 10 12 Daily light integral (mol m Daily light integral (mol m -2-2 d d -1-1 ) Not for publication 2
Evaluating Light-emitting Diodes as an Alternative to High-pressure Sodium Lamps for of Annual Bedding Plant Plugs Materials and Methods Propagation Environment and Culture 77 F constant air temperature 16-h photoperiod 128-cell plug tray Fertilized with 100 ppm N Joshua Craver 1 and Roberto Lopez 2 1 Dept. of Horticulture & Landscape Architecture, Purdue Univ. 2 Dept. of Horticulture, Michigan State Univ. Materials and Methods Light Treatments and DLI Averages French marigold Bonanza Deep Orange HPS Ambient Set Point: 70 µmol m 2 s 1 Avg. DLI: 10.9 mol m 2 d 1 No supplemental Light Avg. DLI: 5.3 mol m 2 d 1 LED Set Point: 70 µmol m 2 s 1 Avg. DLI: 11.0 mol m 2 d 1 Seedling data collected at 14 days Petunia Single Dreams White Zinnia Zahara Fire Seedling data collected at 21 days Seedling data collected at 14 days Not for publication 3
New Guinea Impatiens Divine Blue Pearl Materials and Methods Finishing (after transplant) Light Treatments (Factorial Structure) LED top lighting (70 µmol m 2 s 1 ) HPS (70 µmol m 2 s 1 ) No SL (ambient light only) Light Treatment DLI Averages (Feb. 18 Apr. 19) LED top lighting = 11.7 mol m 2 d 1 HPS = 11.4 mol m 2 d 1 No SL = 8.6 mol m 2 d 1 Seedling data collected at 21 days Results Zinnia Finishing Finishing Lighting Ambient LED HPS Propagation Lighting HPS LED Ambient Young Plant LED Lighting Conclusions LEDs are comparable to HPS for use in young plant production LEDs are suitable for providing supplemental light for plug production with some benefits compared to HPS lamps Compact plugs that have greener foliage Finished plant quality of most species was not significantly influenced by propagation supplemental lighting from HPS or LEDs Picture taken 36 days after transplant End of Production with Red and Blue LEDs Increases Purple Pigmentation of Red Leaf Lettuce and Pennisetum Rubrum in the Greenhouse Under low-light greenhouse conditions, foliage of P. setaceum Rubrum and red leaf lettuce is: Often pale green to light purple Not as aesthetically appealing to consumers W. Garrett Owen and Roberto G. Lopez Not for publication 4
Color is a key component Influences and registers with consumer s initial perception of product quality (Ryder, 1999) Addition of blue (450 nm) light Significantly increased the concentration of anthocyanins in leaf tissue (Stutte, 2009) End-of-production (EOP) Supplemental Lighting: Finishing stage of crop cycle Proposed practice to enhance color Plant Material: Purple fountain grass Rubrum Transplant into 13-cm diameter plastic containers Increase product quality and aesthetic value Red leaf lettuce varieties Initiation Cherokee Magenta Ruby Sky Vulcan End-of-production Lighting Light source Light type Spectral ratio (Red:Blue) Intensity (μmol m 2 s 1 ) Control (No EOP) Photoperiodic --- 4.1 HPS --- 70.0 Light-emitting diodes (LEDs) End of Production Supplemental lighting (SL) 100:0 100.0 50:50 100.0 87:13 100.0 0:100 25.0 0:100 50.0 0:100 100.0 0 days after start of experiment Not for publication 5
Purple fountain grass 'Rubrum Control HPS Red LED 50:50 87:13 Blue LED 4.1 70 100 100 100 25 50 100 µmol 7 days of EOP 14 days of EOP Purple fountain grass 'Rubrum 21 days of EOP Purple fountain grass 'Rubrum 21 days of EOP Control 4.1 µmol HPS 70 µmol Red LED 100 µmol 50:50 100 µmol 87:13 100 µmol Blue LED 25 µmol Control HPS 70 µmol Red LED 100 µmol Blue LED 25 µmol Blue LED 50 µmol Blue 50 µmol Blue LED 100 µmol Blue 100 µmol Purple fountain grass Rubrum No HPS Red LED 50:50 R:B LED EOP 70 100 100 µmol Geranium Black Velvet No HPS Red LED 50:50 R:B LED EOP 70 100 100 µmol 87:13 R:B LED Blue LED 100 25 50 100 µmol 87:13 R:B LED Blue LED 100 25 50 100 µmol 14 days after start of experiment 7 days 14 days after after start start of experiment of experiment Not for publication 6
Lettuce Vulcan HPS Red LED R:B LED Blue LED Control 70 100 100 25 50 100 µmol 5 days of EOP Lettuce Ruby Sky HPS Red LED R:B LED Blue LED Control 70 100 100 25 50 100 µmol 5 days of EOP 7 days of EOP 7 days of EOP 14 days of EOP 14 days of EOP Conclusions Purple Fountain Grass Seven to 14 days of EOP SL of 100 µmol m 2 s 1 red:blue, red or blue LED light Promotes enhanced purple pigmentation of purple fountain grass Rubrum and geranium Black Velvet geranium when grown under a low greenhouse DLI Conclusions Lettuce Five to 7 days of EOP SL of 100 µmol m 2 s 1 red:blue, red or blue LED light Promotes enhanced red pigmentation of lettuce Cherokee, Ruby Sky and Vulcan foliage when grown under a low greenhouse DLI Acknowledgments We also thank the USDA, private horticulture and lighting companies that support our lighting research including: Not for publication 7