Natural Sun Light

By

Jay Holcomb

Terms to Understand

Radiant Energy--the form of energy which is propagated through space in the form of electromagnetic waves.

Radiation--the process by which radiant energy is generated and emitted by a source and propagated through space.

Photosynthetically Active Radiation--energy used for photosynthesis 400-700 nm

Terms to Understand-2

Irradiance--the radiant flux density incident on a surface. This is the amount of radiant energy that is received by an object.

Light--that portion of the electromagnetic spectrum with wave lengths between 380 and 780 nanometers.

Changes in Irradiance

Atmosphere can reduce irradiance 30%

Cloud cover reduces irradiance dramatically

Plant canopy reduces irradiance and shifts spectral quality

Changes in Irradiance-seasonal

Of the total irradiance available December has 3% while June and July have about 14%.

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

Photosynthetically active radiation (PAR) is measured as µmoles/m2/sec.

This is an instantaneous measurement.

It must be summed to get moles/day

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

For a day in June the mean would be 29 with a minimum of 18 and a maximum of 36

For a day in December the mean would be 9 with a minimum of 1 and a maximum of 16

January 6 February 12 March 16 April 20 May 24 June 24 July 26 August 22 Sept 16 October 12 Nov 6 Dec 6 For Grand Rapids by Faust from

GPN

Light Compensation and Saturation Compensation point-

point when Pn is equal to Pr

Saturation Point-point above which an increase in light will not cause an increase in carbon fixation

Statement

“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.”

“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

Increased irradiance increases yield Increased irradiance speeds up flowering Increased irradiance will reduce flower bud

senescence Increased irradiance will improve root growth Increased irradiance will permit greater post

harvest life

Methods of Affecting Irradiance

Angle of Incidence Greenhouse shape Greenhouse orientation Greenhouse cover Amount of structure

above the plants Upkeep of the

greenhouse interior

Shading compound on the roof. Applied about May1-15, wash off by mid-September

Changing plant density and planting patterns

Using reflective materials to reflect sun light to plant

Plant Response to Irradiance

Too High Light– Burned spots on

foliage

– Fading of flower color

– Light green leaves of orchids

Too Low Irradiance– Stretched plants

– Poor quality

– Reduced productivity

– Reduced yield

– Reduced post-harvest life

Light Quality-Phytochrome

Pr is phytochrome that absorbs red light

Pfr is phytochrome that absorbs far-red light. Converted in darkness

Light quality (amount of red and far-red light) will affect phytochrome

Phytochrome affects growth

Pfr/Ptotal controls plant growth

High Pfr/Ptotal produces compact growth (little stem elongation)

Low Pfr/Ptotal produces elongated growth (substantial stem elongation)

How to affect Phytochrome

The red/far-red ratio in sunlight is affected during the day.

During mid-day R/Fr ratio is between 1.05-1.25

During sunrise and set the ratio is 1.15-0.65

As light passes through a plant canopy there is a substantial increase in far-red light.

This has the effect of encouraging stem elongation in the under story plants

Photoperiodism-defined

Response of the plant to the relative length of the day and night.

The response can include flowering, tuber formation, bulb formation, others

Photoperiodism-terms

Critical day (night) length--the point where the response shifts from a long day to a short day response

Facultative (quantative) short day plant--flowers faster with short days

Obligate (qualitive) short day plant--must have short days to flower

Phytochrome affects flowering

P far-red inhibits flowering in Long Night Plants (short day plants)

P far-red promotes flowering in Short Night Plants (long day plants)

Controlling Photoperiod

Create short days by covering plants with blackcloth from 7pm to 8 am

Create long days by incandescent lamps at 10 footcandles from 10 pm to 2 am

Lamps for Lighting

Plant Lighting

Sole source--lamps can be used to provide the only source of energy for the plant

Supplementary--the plants receive some natural light but that is supplemented by light from lamps (Photosynthetic lighting)

Photoperiodic lighting--lamp light is provided for the purpose of providing long day conditions

Lamp Types-Incandescent

Energy provided in the red and far-red region

10% of electricity given off as light

Used for photopereiod control for flowering

Uncomplicated and easy to install

Lamp Types-Incandescent-1

Number of wattages are available

Economical to purchase and install

Can have internal or external reflectors

Lamp Types-Fluorescent

Low pressure gas discharge lamps

UV radiation absorbed by fluorescent powder

Light quality controlled by the phosphor

Use a ballast Efficiency is20%

Lamp Types-Fluorescent-2

Lamps can be located near the plants because operating temp is low

Used as sole source in growth rooms

Cool white plus warm white -- good combination

8’ VHO and HO hot

Lamp Types-HID

High intensity dis-charge (high pressure)

Light produced by electrons moving through gas

Sodium-yellow, mercury-blue-green

Operate with a ballast Efficiency 25%

Lamp Types-HID-2

Cost of lamps and installation is high

Wattages are between 400 and 1000

Most frequently used as supplementary light because high irradiance and small fixture

Supplementary light-plant response Irradiance level times

duration creates plant response

Cost of lighting is irradiance times duration