Learning the Lighting Lingo

Properties of Light Learning the Lighting Lingo Steve Szewczyk and Roberto Lopez Cultivate 2017 Light is a form of energy referred to as electromagnetic radiation. The amount of energy of each light particle is determined by its wavelength Therefore light can vary in: Quality (color and wavelength), Duration (photoperiod), and Quantity or intensity (quantity of light at each wavelength or color) Natural Tech Consulting@gmail.com Jason Avent Rebecca Knight Properties of Light Light and Production Electromagnetic radiation = energy radiated from the sun, spread as electromagnetic waves Photon = particle of electromagnetic radiation Sun s Electromagnetic Spectrum Light quantity Light quality Light duration (intensity) (distribution) (photoperiod) HPS/ MH lamps filters/ shading incandescent/ LEDs LEDs CFL/LEDs Image: http://www.ces.fau.edu/nasa/module-2/radiation-sun.php Root & shoot Photomorphogenesis, Flowering, growth, branching, pigmentation dormancy flower size & number Erik Runkle, MSU Light Quality Overview of Entire Electromagnetic Spectrum Light quality is the relative number of photons of blue, green, red, far-red, and other portions of the light spectrum The wavelength is the distance between waves, and different colors have different wavelengths Units of wavelength are in nanometers (nm or billionth of a meter) Not for Publication 1

Category Wavelength (nm) Effects Short wavelength (high energy) UV C 100 280 Water sterilization UV B 280 320 UV A 320 380 Visible Light Quality 380 780 (PAR 400 700) Stem elongation, anthocyanin Photosynthesis, growth Far red 700 800 Stem elongation, day length perception Infrared 780 2500 Heat Long wavelength (low energy) Shade Avoidance Response As plants grow, they begin to shade one another in a competitive environment (ie. under a forest canopy or tightly spaced greenhouse bench) As shading increases, the red/far-red ratio decreases and promotes stem elongation When stem extension increases in response to shading, it is called a shade avoidance response Canopy Filtering Sunlight R/FR ratio = 1.1-1.2 Green leaf 10-20 times more FR light is transmitted through a leaf than R light (more R light is absorbed) Canopy Filtering Green leaves reflect, transmit and absorb light of different wavelengths Only a small portion of FR (700-800 nm) is absorbed, while most R is absorbed This is why R/FR is reduced for the light transmitted from a leaf Microclimates of leaves PAR Near infrared Short wave includes PAR and part of NIR Long wave Reflection.09.51.30.05 Transmission.06.34.20 0.0 Absorption.85.15.50.95 PAR FR Shade Plants Versus Sun Plants Controlling Light Quality Shade plants (typically grow under a tree canopy) Not affected by the R/FR ratio Amount of FR present does not affect stem elongation Sun plants (typically grow in a sunny environment) Are affected by the R/FR ratio The greater the amount of FR present, the greater the rate of stem elongation Using supplemental lighting with relatively high red and low far-red light Plant spacing Using photoselective filter as covering material or shading curtain (under development) Not for Publication 2

Light Quality Is Influenced by Light Sources Light source R/FR Sunlight 1.15 High pressure sodium 5.9 Incandescent 0.7 LEDs varies Metal halide 3.3 Cool white fluorescent 8.8 Among the commonly used electric light sources, incandescent lamps have the lowest R/FR ratio Plants grown under incandescent lamp have more stem elongation Other lamp sources do not increase stem elongation Photomorphogenesis Photomorphogenesis is the effect of light on plant morphology and architecture. It describes how light changes the shape of plants. High R Low R Low FR High FR 100% blue LED light Cool-white fluorescent Seedlings grown for the same period of time and at the same light intensity Anthocyanin Production LEDs for Night-Interruption Lighting in the Snapdragon Greenhouse Liberty Classic Cherry 9-hour day with 4-hour night interruption 100% Red LEDs 100% Far red LEDs 9-hour short INC lamps Red to Far-Red Ratio day 0.6 140.3 5.0 2.4 1.1 0.7 0.3 0.1 52 41 56 49 47 45 44 44 49 Days to flower at 68 F Erik Runkle, MSU Spectral Energy Distribution Light Quantity Light quantity or intensity is the number of light particles (called photons) capable of performing photosynthesis Plant growth is driven by photosynthesis, which converts water, carbon dioxide, and energy from light into carbohydrates Not for Publication 3

Photosynthetic active radiation (PAR) Humans vs. Plants vs. Pigments The energy used for plant growth is in the visible part of the light spectrum (wave band) of 400 to 700 nanometers (nm) that drive photosynthesis. Lumens are a measure of the total quantity of visible light emitted by a source (lighting for humans) PAR, When measuring light used by plants e units that quantify photons The light absorption of pigments is not a direct indicator of photosynthetic efficiency Photosynthetic active radiation (PAR) Less than half of the energy (43%) from the sun is in the photosynthetically active radiation (PAR) range of 400 to 700 nm Instantaneous Light Photosynthetic photon flux density (PPFD) the number of photons (PAR) that fall within a square meter per second. Unit: µmol m-2 s-1 Photons are packets, or particles, of light energy Figure adapted from research by Daryl Myers Erik Runkle, MSU Photosynthetic active radiation (PAR) Increasing energy in the PAR range, up to an optimal light intensity maximizes photosynthesis, plant growth, and quality Measuring Light Light can be measured instantaneously or cumulatively Instantaneous readings provide a snapshot of the light environment Cumulative readings more accurately reflects light received over the course of a day Not for Publication 4

Light Units Photometric (lux or foot candles) Includes visible light Quantum (µmol m 2 s 1 ) includes PAR Radiometric (w m 2 ) Includes radiant energy Light Units Photometric (lux or foot candles) Is the most common unit used to measure instantaneous light by U.S. growers It represents the amount of light visible to the human eye Light Units Quantum (µmol m 2 s 1 ) Measures the amount of photosynthetically active radiation (PAR), 400 to 700 nm This quantum unit quantifies the number of photons of light used in photosynthesis that fall in a square meter every second Measuring Instantaneous Light Hand-held quantum meters are available with a single-or multiple-diode sensor Measuring Instantaneous Light Measuring Instantaneous Light A single-diode sensor is smaller and easier to carry A multiple-diode sensor takes a reading from each diode and reports the average light level, giving a more representative reading Quantum meters may also have the ability of switching between measuring electric and sun light Natural light levels are continuously changing and a single measurement in time does not accurately represent the amount of light a plant has received in a day However, they can be used to make decisions such as whether to pull shade cloth or when to turn on supplemental lamps Not for Publication 5

Daily Light Integral DLI) The term daily light integral (DLI) describes this cumulative amount of light (photons of light) that an area or location receives during one day. Therefore, DLI is the cumulative amount of photosynthetic light received in 1 square meter of area (10.8 sq. ft.) each day. 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) Varies due to factors that influence light intensity and duration: Time of the year (sun s angle) Location and cloud cover Day length (photoperiod) Greenhouse glazing/ covering(s) Structure and obstructions Hanging baskets Supplemental lights Daily Light Integral (DLI) DLI is expressed in units of moles of light (mol) per square meter (m -2 ) per day (d -1 ) or mol m -2 d -1. Values from sunlight outdoors vary from 3 (winter) to 60 mol m -2 d -1 (summer). In a greenhouse, values seldom exceed 30 mol m -2 d -1 because of shading which can reduce light by 40 to 70%. Target minimum DLI inside a greenhouse are 10 to 12 mol m -2 d -1. Outdoor Daily Light Integral DLI in a Greenhouse 40 30 In a greenhouse without shade In a greenhouse with 50% shade Winter with HPS on for 16 hrs. (4.3 mol. m -2. d -1 ) Daily Light Integral (mol. m -2. d -1 ) 20 10 0 feb 10 mar 10 apr 10 may 10 june 10 july 10 aug 10 sept 10 oct 10 nov 10 dec 10 jan 11 feb 11 mar 11 apr 11 may 11 june 11 july 11 aug 11 sept 11 oct 11 nov 11 dec 11 jan 12 feb 12 mar 12 apr 12 may 12 june 12 july 12 aug 12 sept 12 oct 12 nov 12 dec 12 jan 13 feb 13 mar 13 apr 13 may 13 june 13 Month aug 13 sept 13 oct 13 Not for Publication 6

Plant Responses to Higher DLI Smaller and thicker leaves More and larger flowers Reduced time to flower (partly due to temperature) Increased branching Increased stem diameter Increased root growth of plugs and cuttings Estimating DLI Inside the Greenhouse If we have an estimate of outside light, we can estimate DLI inside the greenhouse Central Ohio: 10-15 mol m -2 d -1 outside January 10 0.5 = 5 mol m-2 d-1 20 0.5 = 10 mol m-2 d-1 Your DLI: Between 7.5 and 10 mol m-2 d-1 Calculating Daily Light Integral for Sunlight in a Greenhouse Calculating DLI for sunlight in a greenhouse is more difficult than calculating DLI for a constant intensity light source: it changes constantly!!! DLI (mol/ sq m day) 18 16 14 12 10 8 6 4 2 10/31 11/20 12/10 12/30 01/19 Date First, take the average of discrete time periods: hourly. For example: 0, 0, 0, 0, 0, 44, 102, 198, 255, 410, 454, 600, 532, 627, 466, 376, 303, 187, 91, 45, 47, 44, 43, 0 Heidi Lindberg, MSU Heidi Lindberg, MSU DLI CALC Online Calculator (GOOGLE: DLICALC) DLI Calc: Estimate Your Supplemental DLI Allows you to estimate the supplemental DLI from your supplemental light source Not for Publication 7

Allows you to estimate the hours of lamp operation to achieve a target supplemental DLI Estimate Hours of Operation Methods to Increase DLI Minimize overhead obstructions such as hanging baskets. Make sure your glazing is properly cleaned (ie. whitewash, dust, algae removed). Provide supplemental lighting from High Pressure Sodium Lamps (HPS), Metal Halide or Light Emitting Diodes (LEDs). Photoperiod Photoperiod Photoperiod combines the two Greek roots for light and duration of time to describe the duration of the day that is light Photoperiod influences many aspects of plant growth and development including dormancy, storage organ formation and most importantly for many greenhouse producers, flowering The interval of time (day length) between sunrise and sunset changes throughout the year For example, in the U.S., which is in the northern hemisphere, day length increases from December 21 st until June 21 st, after which it decreases Photoperiod Natural Photoperiod during the Year Seasonal fluctuation in day length becomes more dramatic as the latitude increases Seattle For example, the day length in Miami (25.8 N latitude) ranges from approximately 10 ½ hours to a little more than 13 ½ hours The day length in Seattle (47.6 N latitude) ranges from 8 ½ to 16 hours Miami Erik Runkle, MSU Not for Publication 8

Natural Photoperiod during the Year Photoperiodic Responses Plants are classified as: Short-day plants Long-day plants Day-neutral plants Furthermore, responses may be categorized as: Obligate (qualitative) Facultative (quantitative) Erik Runkle, MSU Photoperiodic Responses Photoperiodic Responses Photoperiod refers to the duration of light hours in the day It is actually the duration of darkness that is the signal Truncating, extending the day or interrupting the night are the three strategies used to manage photoperiodic plant responses When to Provide Long-day Lighting? Lights for Creating Long Days Most long-day (LD) plants flower faster when the night length is less than approx. 10 hours Long-day lighting can be used to delay flowering of short day crops (ie. poinsettia) In the northern hemisphere, provide LD lighting from Sept. 1 to April 15 Incandescent (INC), compact fluorescent (CFL), light emitting diodes (LEDs) stationary, moving or cyclic highpressure sodium Low intensity lighting of 10 foot-candles (100 lux or 2 µmol m -2 s -1 ) at plant height is adequate for most greenhouse crops Not for Publication 9

Creating Long-day Lighting Day-extension Lighting Day-extension lighting: Is the use of artificial light to extend the length of the day Begins at sunset and ends when the desired photoperiod is achieved If you want to provide a 16-hour photoperiod and sunrise is at 7 AM and sunset is at 7 PM, you would light from 7 PM to 11 PM Creating Long-day Lighting Night interruption/ night break lighting/ mum lighting: By interrupting the night length, plants will not perceive a long night, but rather a short night (or long day) Generally 4 hours of lighting are used in the middle of night (ie. 10 PM to 2 AM) Cyclic Long-day Lighting (LD) Three methods: INC lamps are on for 5 to 10 minutes every 30 min. during the lighting period HID lamps are mounted on a moving boom that passes over the crops for at least four hours during the night Fixed HID with an oscillating reflector/ luminaire (ie. Beamflicker) Long-day Lighting (LD) Examples of Cyclic Lighting 12 hours 12 hours 12 hours 6:00 am 12:00 pm 6:00 pm 12:00 am 6:00 am Erik Runkle, Michigan State Univ. HID mounted to a moving boom Fixed HID with an oscillating reflector/luminaire Not for Publication 10

Creating Short Days (SD) Under LD conditions, SD plant responses can be achieved by shortening the day length Materials commonly used include: Opaque cloth or fabric that does not allow light to penetrate, commonly referred to as black cloth or blackout cloth Woven blankets consisting of aluminum and plastic strips Black plastic When to Pull and Retract Black Cloth? Black cloth or plastic is traditionally pulled at 5 p.m. and retracted at 8 a.m. to coincide with normal working hours When to Pull and Retract Black Cloth? Automatic systems that are operated by a timer or environmental computer can be used for individual benches or an entire greenhouse Creating Short Days (SD) Potential problems: Accumulation of heat under the fabric or plastic Plastic can collapse on plants due to condensation Sides not properly pulled New Book on Horticultural Lighting FOR MORE INFORMATION Updated and expanded from 2004 Lighting Up Profits book edited by Fisher and Runkle 18 chapters, 20 chapter authors, edited by Lopez and Runkle Published by Meister Media (parent company of Greenhouse Grower) Available in print and digital versions on Amazon Natural Tech Consulting@gmail.com Jason Avent Rebecca Knight http://msue.anr.msu.edu/topic/info/floriculture Not for Publication 11