Environmental Factors
Plant life depends on light energy for
food production through
photosynthesis.
 Plants convert the energy to a form of
chemical energy.
 Three key aspects of light effect plant
growth

 Color
 Duration
 Intensity
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Visible light (light we see) is a small
segment of all the radiant energy (rays)
given off by the sun.
Based on their wavelengths, the rays have
been placed on an, Electromagnetic
Spectrum.(click)
Sunlight contains a blend of visible colors.
Each color has a slightly different
wavelength
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Light quality refers to the color or wavelength
reaching the plant surface.
Sunlight can be broken up by a prism into
respective colors of red, orange, yellow,
green, blue, indigo, and violet. (ROY G BIV)

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R - Red and blue light have the greatest effect on
plant growth.
O - Incandescent light is high in the red or orange
range but generally produces too much heat to be
a valuable light source.
Y - Yellow
G - Green light is least effective to plants as most
plants reflect green light and absorb very little. It is
this reflected light that makes them appear green.
B - Blue light is primarily responsible for vegetative
growth or leaf growth.
I - Indigo
V - Fluorescent "grow" lights have a mixture of red
and blue colors that attempts to imitate sunlight as
closely as possible.
The light reflected has little affect on the plant.
 In plants, blue & red have the greatest
influence on plant growth.
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Blue:
◦ Effects photosynthesis

Red:
◦ Effects flowering and growth
Environmental Factors

Plants are responsive to the length of time
they are exposed to light.

A mechanism in the plant detects the length
of the light period.

A plant’s response to the length of light is
known as, Photoperiodism.
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Different plants respond differently to the duration of
light.
Plants are broken into three categories:
 Short-day plants (Long-nights): Initiate flowering as
the night grow longer than 12 hours.
 Long-day plants (Short-night period): Initiate
flowering as the nights grow shorter than 12 hours.
 Day-neutral plants (unaffected) Are those plants that
do not appear to respond to the change of day length.
Short Day Plant
critical
day length
24 hours
light
dark
No
Yes
No
Flowers?
light
critical
day length
24 hours
Long Day Plant
dark
Yes
No
Yes
Flowers?
Environmental Factors
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Involves brightness.

Depends largely on the angle of the sun, clouds, and the
dust in the atmosphere.

Measured in foot candles

Light intensity is the greatest in the summer months.
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All plants have different terms of light intensity.

Light intensity can influence plant development for
better or for worse.
 Is the amount of light distributed by a single candle one-foot
away.
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http://www.youtube.com/watch?v=lgFOnMwo3A&feature=relmfu
http://www.youtube.com/watch?v=UQ_QqtXo
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LAB SHEET
“How Do I Look in the Light?”