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Modifying Light Intensity for Optimal Growth in Greenhouses

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This guide explores the importance of light intensity and quality in greenhouse settings, focusing on the range of wavelengths (400-800 nm) and intensity levels (100-300 mmol/s/m²) necessary for optimal plant growth. It covers various types of lamps, including incandescent, fluorescent, and high-intensity discharge (HID) options like high-pressure sodium (HPS) and low-pressure sodium (LPS) lamps. The analysis includes commercial applications, benefits for crop quality and efficiency, and practical methods for adjusting light intensity, such as shading compounds and reflective surfaces.

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Modifying Light Intensity for Optimal Growth in Greenhouses

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  1. XIV. MODIFYING LIGHT INTENSITY

  2. A. Supplementary Artificial Light 1.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

  3. 2. Types of Lamps a. Incandescent • primarily red light • point source • short life b. Fluorescent • deficient in red? • 2', 4', 8' lengths • greater uniformity • shadows

  4. c. Combination: -fluorescent lamps -incandescent lamps • complete spectrum • shadows • suitable for growth room

  5. d. High intensity discharge (HID) • Mercury vapor • not used today • Metal halide • good spectrum • lower eff. than HPS & LPS

  6. High Pressure Sodium • high light intensity • 400-1000 watt • eff. conversion of energy • Low Pressure Sodium • narrow band of light • efficient conversion

  7. New Lights for Greenhouses Sulfur and microwave Diode

  8. 3. Commercial Application a. 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

  9. 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

  10. 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

  11. High pressure sodium light arrangement

  12. Growth room

  13. 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

  14. 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

  15. 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

  16. B. Increasing light intensity • Clean covering • White or reflective surface • Reduce shade producing items

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