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Importance of Light for Plant Growth and Development

Light is crucial for photosynthesis, chlorophyll production, photomorphogenesis, and anthocyanin production in plants. It influences energy conversion, translocation within plants, and even affects abscission. This text explores different sources of light, light measurements, factors affecting light penetration, and artificial lighting considerations. It also delves into light quality, Photosynthetically Active Radiation (PAR), choosing artificial lights, and ways to increase artificial light for optimal plant growth.

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Importance of Light for Plant Growth and Development

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  1. Why is light important? 1.) Photosynthesis 6CO2+ 12H2O(chl & light) C6H12O6 + 6O2 + 6H2O 2.) Needed for chlorophyllproduction 3.) Photomorphogenesis - development of certain plant parts, esp. flower initiation and development, seed germ...

  2. Why is light important? 4.) Anthocyanin production 5.) Light is energy! Some is converted to heat when it strikes a plant surface 6.) Light influences translocation in the plant 7.) Light can affect abscission (dropping of plant parts) when intensity suddenly changes

  3. Lightintensity -Refers to brightness -Often the limiting factor for growing or maintaining plants indoors

  4. Light measurement Light can be measured in many ways! - Light meter (photoelectric cell) Footcandle = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 foot Lux = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 meter

  5. Conversion: 1 fc = 11.1 lux These units measure only visible light (what the eye can see!) For scientific reporting of light quantity, you might hear the following terms: candela lumen photon flux quanta joules

  6. Sources of light for an interior 1.) Natural (sunlight) 2.) Artificial (bulbs and tubes) 3.) Combination of the above

  7. Sunlight Factors affecting light penetration into a room: 1.)Windows -type (glass/plastic/glazing) -reflection -barriers (overhangs, screens, curtains, shades, buildings and plants outside, dirt, etc...) -orientation (N, S, E, W)

  8. Sunlight 2.) Latitude (distance away from the equator) 24 22 20 Burlington 18 16 Atlanta 14 12 Equator 10 8 6 4 2 J F M A M J J A S O N D J (calendar year)

  9. Sunlight 3.) Geographic region -annual cloud cover -atmospheric pollution -humidity -elevation

  10. Artificial light Supplemental to sunlight -extend hours of light -increase intensity of light Sole source -role: room lighting plant lighting combination

  11. Artificial light Considerations not necessary with sunlight: spectral emission = range of colors produced by the light Light Quality!!! Ultra- violet Gamma rays Infrared Radio X-rays Visible Light (nanometers) y e l l o w i n d e g o v i o l e t o r a n g e b l u e g r e e n r e d 380 430 470 500 560 600 650 760

  12. Photosynthetically Active Radiation (PAR) Range = 400 - 700nanometers Based on length of each wavelength of light ~~~~~~~~~~~~~~~~~~~~ Chlorophyll and associated pigments utilize light energy primarily in the blue(430 nm) and red (670 nm)

  13. Choosing artificial lights Sources: Incandescent bulb Pros: -small -no special fixtures -dramatic -range of wattages available Cons: -light is concentrated -7% of energy usable light -90% of energy heat! -short life (750 hrs.) -high in red/orange & low blue

  14. Fluorescent tubes (cool-white, warm-white, daylight) Pros: -diffuse light, new fixtures avail. -efficient! (7x incandescent!) -22% of energy usable light -cool! 36% of energy heat -last 8,000 - 9,000 hrs (15x longer than incandescent!) Cons: -work best if 70 - 90oF - traditionalfixtures bulky -low far-red emission -contain mercury -emit ultraviolet light

  15. Cool white Warm white

  16. Daylight fluorescent vs. Incandescent bulb 100 90 80 70 60 50 40 30 20 10 0 Fluorescent Relative energy Incandescent 400500 600 700 (nanometers)

  17. Sodium vapor lamps(HID lighting)Pros: -25-35 % of energy visible lightCons: -yellow/orange/red spectral emission only! -large ballast (requires special lighting fixtures)

  18. Reflected Absorbed What happens when light contacts a leaf? Transmitted

  19. Ways to increase artificial light: • Added white reflectors to fluorescent fixtures • Paint surrounding walls white • Regularly clean tubes to remove dust • Regularly clean plants to remove dust • Change tubes regularly • Keep plants centered under fluorescent tubes

  20. Natural vs. Artificiallight intensities • Noon sun during summer can measure 10,000fc • Cloudy winter day: 500-2,000 fc • Inside rarely exceeds 1,300fc • typical office 20-30 fc • typical living room • day: 10-1,000 fc • night: 5-10 fc

  21. Minimum light required for plant maintainance??? 100 fc

  22. -Light quantity- Total light per day = footcandles of light x hours of light/day Example: 100 fc x 16 hrs of light/day 1,600 fc hours/day Sometimes, extending the daylength can compensate for a lower light intensity...

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