Light

1
Light Plant Growth p. 97-139

• Quality - wavelength - color
• determines energy
• Quantity - intensity
• amount given off by source
• amount striking unit area
• Duration - photoperiod
• length of lighted period

2
Light Quality
3
Light Quality
4
Photosynthesis Light Quality

• PAR
• Photosynthetically active radiation
• 400-700 nm
• Chlorophyll has greater absorbance of blue light
  and orange - red light
• little absorption of green (500-600nm)

5
Other influences of Light Quality

• Preferential Light Absorbance
• influence internode length
• increase fr, increase internode length
• influence leaf movement - sensitive plant,
  soybean
• use red mulch to reflect red light into canopy -
  increase yield in some crops

6
Light Quantity/Intensity
7
Light Saturation

• Shade leaves vs sun leaves
• leaves developed in shade have lower light
  saturation point or optimum intensity than leaves
  that have developed in direct sunlight.
• plants adapted to low light conditions good for
  interiorscaping

8
Light Intensity - Too much light

• sunburn
• photobleaching
• stunting
• reduced leaf size
• fading flowers

9
Light Intensity- Too little light

• reduced flowering
• weak, long thin stems
• poor yield (low photosynthesis)
• etiolation - lack of light - poor chlorophyll
  development

10
Modify Light Intensity (Increase)

• Increase plant spacing
• Add artificial light
• High intensity discharge (HID)
• greater photosynthesis
• Fluorescent Lights
• Blue, green, yellow 400-600nm
• low intensity, less effective than HID
• Incandescent Lights
• low in blue light, greater red light
• low intensity
• predominately for photoperiod control

11
Decrease Light Intensity

• Decrease plant spacing - greater density or
  crowding cause shading
• shade cloth, screen, shading paint, lath houses

12
Light Duration
13
Light Duration

• Daylength/ Photoperiod
• The longer the plant receives light of sufficient
  intensity, the more photosynthesis occurs
• greater growth
• photoperiod influences seed germination,
  flowering, branching, stem elongation, onset of
  dormancy, fall color, storage organ development
  etc.

14
Short Day Plants

• Critical day length - species dependent
• plant initiate flowers after receiving a specific
  number of photoperiod cycles
• usually less than 12 hours of light
• Chrysanthemums, Poinsettias, Christmas Cactus,
  june bearing strawberries - initiate flowers
  under SD
• long days promote vegetative growth in these
  plants

15
Long day

• plants flower after receiving specific number of
  photoperiod cycles
• usually greater than 12 hours of light
• lettuce, radishes, spinach flower under LD
• short days promote vegetative growth

16
Light Duration Flowering

• Day neutral plant
• flower initiation is not dependent on daylength
• plant will flower under long or short photoperiods

17
Modify Light Duration

• Shorten photoperiod - black cloth in greenhouse
• Extend photoperiod - incandescent lights (Mum
  Lighting)
• rich in red and far red light

18
Photoperiod Light Quality

• Phytochrome - photoreactive pigment that responds
  to Red Far-red light.
• Pr absorbs red light(660 nm) Pfr absorbs far
  red light (730 nm)
• Add light at end of photoperiod or interrupt
  night and influence conversion of phytochrome
• Not all light responses dependent on phytochrome
• other pigments can be involved