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XIV. MODIFYING LIGHT INTENSITY
A. Supplementary Artificial Light1. Light Intensity and Quality
•Quality–400-800 nanometers
• Intensity–100-300 mmols/sec/m2
–500-2000 ft. cds.•Distance vs. Intensity–decrease the greater the
distance
2. Types of Lampsa. Incandescent• primarily red
light• point source• short life
b. Fluorescent• deficient in red?• 2', 4', 8' lengths• greater
uniformity• shadows
c. Combination:
-fluorescent lamps
-incandescent lamps• complete spectrum
• shadows
• suitable for growth room
d. High intensity discharge (HID)• Mercury vapor–not used today
• Metal halide–good spectrum– lower eff. than
HPS & LPS
• High Pressure Sodium–high light
intensity
–400-1000 watt–eff. conversion
of energy
• Low Pressure Sodium–narrow band of
light–efficient
conversion
New Lights for Greenhouses
Sulfur and microwave Diode
3. Commercial Applicationa. Crops
• Roses, chrysanthemums, seedlings, lettuce, tomatoes
b. Benefits• timing• quality• less prod. time; lower
cost• less fuel costs• increasing branching• increased keeping
quality
• roses; fewer blind shoots
3. Commercial Application (contu.)c. Where used• northern latitudes• growth rooms
d. Installation/operating costs• fixture + ballast $150+• fixture + installation
$2.25/sq. ft.• operation:
$1.50/sq.ft./yr• depreciation• interest on money
borrowed
3.Commercial Application (contu.)
e. Management
•Greenhouse
–HPS
• 400watt; spaced 10’ x 10’: 10 ft above plant
• 30-60 umols/sec/m2; 280-460 ft.cd.
•Oct to Apr
• night & cloudy days
High pressure sodium light arrangement
• Growth room
Growth room• 20 sq. ft.• 2 ft. above plants
– 106 umols/sec/m2: 750 ft.cd.• 7 tubes: @ 40
watts
– 200 umols/sec/m2: 1400 ft.cd.• 13 tubes: @ 40
watts
3. Commercial Application (contu.)f. Accumulated light• 200 umol/sec/m2
for 18 hrs.–equals 23
mol/day/m2
• Summer - natural light–48 mol/day/m2
• Winter - natural light–19 mol/day/m2
A. Reducing light intensity- Why- External• shading compounds–Latex paint: 1 part to 8-10
parts H2O–Saran cloth
– Internal permanent• Saran cloth•Aluminum strips
– Internal movable
B. Increasing light intensity
–Clean covering
–White or reflective surface
–Reduce shade producing items