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