Why is light important?

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Why is light important?

• 1.) Photosynthesis
• 6CO2 12H2O (chl light) C6H12O6 6O2
  6H2O
• 2.) Needed for chlorophyll
  
  production
• 3.) Photomorphogenesis - development of certain
  plant parts, esp. flower initiation and
  development, seed germ...

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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

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Light intensity

• -Refers to brightness
• -Often the limiting factor for growing or
  maintaining plants indoors

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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

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• 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

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Sources of light for an interior

• 1.) Natural (sunlight)
• 2.) Artificial (bulbs and tubes)
• 3.) Combination of the above

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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)

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Sunlight

• 2.) Latitude
• (distance away from the equator)

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22
20
Burlington
18
16
Atlanta
14
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Equator
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8
6
4
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J F M A M J J A S O N D
J (calendar year)
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Sunlight

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

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Artificial light

• Supplemental to sunlight
• -extend hours of light
• -increase intensity of light
• Sole source
• -role room lighting
• plant lighting
• combination

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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
v i o l e t
i n d e g o
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
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Photosynthetically Active Radiation (PAR)

• Range
• 400 - 700 nanometers
• 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)

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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

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• 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
• - traditional fixtures bulky
• -low far-red emission
• -contain mercury
• -emit ultraviolet light

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Cool white
Warm white
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Daylight fluorescent vs. Incandescent bulb
100 90 80 70 60 50 40 30 20 10 0
Fluorescent
Relative energy
Incandescent
400 500 600 700
(nanometers)
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Sodium vapor lamps (HID lighting) Pros -25-3
5 of energy visible light Cons -yell
ow/orange/red spectral emission only! -large
ballast (requires special lighting fixtures)
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• What happens when light contacts a leaf?

Reflected
Absorbed
Transmitted
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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

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Natural vs. Artificiallight intensities

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

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Minimum light required for plant maintainance???

• 100 fc

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-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...