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Chap 9. Light and Lighting
Solar Radiation Nature of Solar Radiation Light Quality, Intensity, and Duration Atmospheric Window Greenhouse Effect
Light Intensity Measurements Radiometric Method Photometric Method
Lighting for Photosynthesis Purpose Light Sources Application
Lighting for Photoperiod Control Purpose Light Sources Application
Concept of LightRadiation: A process of emitting energy in the form of electromagnetic
waves or particles (photons). It ranges from cosmic rays, gamma rays, x-rays, UV lights, visible light, to infrared and radio waves.
Light: That portion of radiation perceived or the light-restricted portion of spectrumIrradiation: A process by which a surface is illuminated or irradiated (i.e., irradiation
of flower buds with x-ray to induce mutation).
Visible Light Spectrum
The Solar Radiation
The Influence of Atmosphere
Courtesy: NASA
Atmospheric Windows
http://csep10.phys.utk.edu/astr162/lect/light/windows.html
The interaction of electromagnetic radiation with atmosphere allows only light in certain waive length regions to penetrate the atmosphere well. These regions are called atmospheric windows. The filtration of radiation is largely due to CO2, zone, water vapor in the atmosphere.
Composition of the Visible Light
Source: NASA
Spectral Ranges of Visible Lights
• Violet 0.4 - 0.446 µm
• Blue 0.446 - 0.500 µm
• Green 0.500 - 0.578 µm
• Yellow 0.578 - 0.592 µm
• Orange 0.592 - 0.620 µm
• Red 0.620 - 0.7 µm
• Infrared 0.7 - 0.9 µm
Light Quality
1. What does it mean?
What spectrum of light does it involve? (Red, blue, green, orange, or infrared lights, etc.)
2. Measurements
a. Wave lengths: distance from peak to peak
or valley to valley in units of nm or µmµm = 10-3 mm nm = 10-6 mm Å = 10-3 nm
b. Wave number: number of waves per cm of light (number/cm)
c. Frequency: number of cycles per second (cycles/sec, cps)Hertz (Hz) = 1 cycle/secMega Hz = 1 million Hz
Light Intensity
1. What does it mean?
How much irradiated on the surface (Quantity)
2. Radiometric measurements
a. Light intensity measured in terms of power of radiation on a unit surface area
Power = energy/unit time Intensity = power/unit area, energy/unit area per unit time
b. Measurement units: Joules cm-2 sec-1, watts cm-2,BTU ft-2 hr-1, kcal cm-2 hr-1
c. The shorter the wave length, the more the energy available.
3. Radiometric measurements
a. Light intensity expressed in terms of illuminance or how bright the light is (visible radiation only)
b. Measurement units: Foot candles, lumens, lux, µmol m-2 sec-1
c. Relationships: 1 lux = 1 lumen m-2
1 foot candle = 10.76 lux
4. Factors affecting light intensity a. Moisture in the air No. of clear days in January: 70-80% in AZ, 30-40% in NY b. Topography c. Pollutants in the air (PAN, SO2, NOx, etc.)
Duration of Light
1. What does it mean?
How long the light was on
2. Factors that affect light duration
a. Time of the year (seasonal variation)b. Latitudes (both northern an southern hemisphere) Fargo: 56.5 N
3. Photoperiod responses
a. Long day plants (short night plants)Requires days longer than 16 hours to bloomAster, petunia, potato
b. Short day plants (long night plants)Requires days shorter than 13 hours to bloomChrysanthemum, poinsettia, kalanchoe
c. Mechanism of responsesPhytochrome systemP660 – red light absorbing formP730 – far-red light absorbing form
Influence of Photoperiod on Flowering
Spectral Distribution of Various Lamps
Sunlight
Incandescent lamp
Fluorescent lamp
PAR region
Red-Infrared region
400 nm 700 nm
Ra
dia
nt
En
erg
y
Spectral Distribution of Various Lamps
Spectral distribution of selected fluorescent lamps
High Light Intensity Discharge (HID) Lamps
Mercury Lamps
Mercury Vapor Lamp
High Pressure Sodium Lamps Metal Halide Lamps
Lighting for Photosynthesis
Lighting for Photosynthesis
Quebec, Canada
Influence of Photoperiod on Poplar Tree
Left - Short Day Grown
Right - Long Day Grown
“Black-Clothing” to Shorten Day Length
Automation of Shading for Photoperiod ControlBergen’s Greenhouse, Detroit Lakes, MN
Cut Chrysanthemum ProductionSalinas, California
Day Length Control for Cut Chrysanthemum Production in Florida
Year Round Production of Potted Mums Palisade Greenhouse, Colorado
Black cloth canvas is used to cover plants during short-day treatment