Natural Sun Light By Jay Holcomb

Terms to Understand 4 Radiant Energy--the form of energy which is propagated through space in the form of electromagnetic waves. 4 Radiation--the process by which radiant energy is generated and emitted by a source and propagated through space. 4 Photosynthetically Active Radiation-- energy used for photosynthesis nm

Terms to Understand-2 4 Irradiance--the radiant flux density incident on a surface. This is the amount of radiant energy that is received by an object. 4 Light--that portion of the electromagnetic spectrum with wave lengths between 380 and 780 nanometers.

Changes in Irradiance 4 Atmosphere can reduce irradiance 30% 4 Cloud cover reduces irradiance dramatically 4 Plant canopy reduces irradiance and shifts spectral quality

Changes in Irradiance-seasonal 4 Of the total irradiance available December has 3% while June and July have about 14%. 4 Solar radiation in December is about 1/3 of that in June at latitudes near 40°* –*Giacomelli and Roberts, HortTech 3/93

Definition--Moles/day 4 Photosynthetically active radiation (PAR) is measured as µmoles/m 2 /sec. 4 This is an instantaneous measurement. 4 It must be summed to get moles/day 4 To determine moles/day multiply times 60 sec/min times 60 min/hour times 24 hr/day then divide by 1,000,000 to get moles/day.

Moles/day 4 For a day in June the mean would be 29 with a minimum of 18 and a maximum of 36 4 For a day in December the mean would be 9 with a minimum of 1 and a maximum of 16 4 January6 4 February12 4 March 16 4 April20 4 May24 4 June24 4 July26 4 August22 4 Sept16 4 October12 4 Nov6 4 Dec6 4 For Grand Rapids by Faust from GPN

Light Compensation and Saturation 4 Compensation point- point when Pn is equal to Pr 4 Saturation Point-point above which an increase in light will not cause an increase in carbon fixation

Statement 4 “A successful grower is one who can cause the plant to produce the maximum amount of fresh weight of acceptable quality from a given amount of dry weight.” 4 “Solar radiant energy and temperature determine the quantity of photosynthates available for plant growth, whereas nitrogen and moisture levels determine how they will be utilized by the plant.”

Plant Response to Irradiance 4 Increased irradiance increases yield 4 Increased irradiance speeds up flowering 4 Increased irradiance will reduce flower bud senescence 4 Increased irradiance will improve root growth 4 Increased irradiance will permit greater post harvest life

Methods of Affecting Irradiance 4 Angle of Incidence 4 Greenhouse shape 4 Greenhouse orientation 4 Greenhouse cover 4 Amount of structure above the plants 4 Upkeep of the greenhouse interior 4 Shading compound on the roof. Applied about May1-15, wash off by mid-September 4 Changing plant density and planting patterns 4 Using reflective materials to reflect sun light to plant

Plant Response to Irradiance 4 Too High Light –Burned spots on foliage –Fading of flower color –Light green leaves of orchids 4 Too Low Irradiance –Stretched plants –Poor quality –Reduced productivity –Reduced yield –Reduced post-harvest life

Light Quality-Phytochrome 4 Pr is phytochrome that absorbs red light 4 Pfr is phytochrome that absorbs far-red light. Converted in darkness 4 Light quality (amount of red and far-red light) will affect phytochrome

Phytochrome affects growth 4 P fr /P total controls plant growth 4 High P fr /P total produces compact growth (little stem elongation) 4 Low P fr /P total produces elongated growth (substantial stem elongation)

How to affect Phytochrome 4 The red/far-red ratio in sunlight is affected during the day. 4 During mid-day R/Fr ratio is between During sunrise and set the ratio is As light passes through a plant canopy there is a substantial increase in far-red light. 4 This has the effect of encouraging stem elongation in the under story plants

Photoperiodism-defined 4 Response of the plant to the relative length of the day and night. 4 The response can include flowering, tuber formation, bulb formation, others

Photoperiodism-terms 4 Critical day (night) length--the point where the response shifts from a long day to a short day response 4 Facultative (quantative) short day plant-- flowers faster with short days 4 Obligate (qualitive) short day plant--must have short days to flower

Phytochrome affects flowering 4 P far-red inhibits flowering in Long Night Plants (short day plants) 4 P far-red promotes flowering in Short Night Plants (long day plants)

Controlling Photoperiod 4 Create short days by covering plants with blackcloth from 7pm to 8 am 4 Create long days by incandescent lamps at 10 footcandles from 10 pm to 2 am

Lamps for Lighting

Plant Lighting 4 Sole source--lamps can be used to provide the only source of energy for the plant 4 Supplementary--the plants receive some natural light but that is supplemented by light from lamps (Photosynthetic lighting) 4 Photoperiodic lighting--lamp light is provided for the purpose of providing long day conditions

Lamp Types-Incandescent 4 Energy provided in the red and far-red region 4 10% of electricity given off as light 4 Used for photopereiod control for flowering 4 Uncomplicated and easy to install

Lamp Types-Incandescent-1 4 Number of wattages are available 4 Economical to purchase and install 4 Can have internal or external reflectors

Lamp Types-Fluorescent 4 Low pressure gas discharge lamps 4 UV radiation absorbed by fluorescent powder 4 Light quality controlled by the phosphor 4 Use a ballast 4 Efficiency is20%

Lamp Types-Fluorescent-2 4 Lamps can be located near the plants because operating temp is low 4 Used as sole source in growth rooms 4 Cool white plus warm white -- good combination 4 8’ VHO and HO hot

Lamp Types-HID 4 High intensity dis- charge (high pressure) 4 Light produced by electrons moving through gas 4 Sodium-yellow, mercury-blue-green 4 Operate with a ballast 4 Efficiency 25%

Lamp Types-HID-2 4 Cost of lamps and installation is high 4 Wattages are between 400 and Most frequently used as supplementary light because high irradiance and small fixture

Supplementary light-plant response 4 Irradiance level times duration creates plant response 4 Cost of lighting is irradiance times duration