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