Role of Light in Plants Video Lecture - NEET

light is one of the environmental
factors that affect plant growth there
are three principal characteristics of
light that affect plant growth these are
quality quantity and duration this video
will focus on light quality what is
light quality light quality refers to
the color or wavelength of light visible
light is electromagnetic radiation that
is visible to the human eye
visible light consists of wavelengths
and arranged from about 380 nanometers
to about 740 nanometers the visible
light range is located between the
invisible infrared which is found at
longer wavelengths and the invisible
ultraviolet which is found at shorter
wavelengths sunlight supplies a complete
range of wavelengths light quality
refers to the spectral distribution of
light or the relative number of photons
of blue green red far red and other
portions of the light spectrum emitted
from a light source some of these
portions are visible whereas others are
not light wavelengths are measured in
nanometers
a nanometer abbreviated in m is one
billionth of a meter differences in the
light spectrum blue light green light
and red light make up the spectrum of
light primarily used for photosynthesis
blue light is the portion of light that
has wavelengths between 400 and 500
nanometers green light is the portion of
light that has wavelengths between 500
and 600 nanometers red light is the
portion of light that has a wavelength
between 600 and 700 nanometers about
half the sun's radiation falls within
the photosynthetic wave band the rest of
the sun's energy has shorter wavelengths
including ultraviolet light or longer
wavelengths which includes far red light
and infrared radiation effective light
quality on plant growth plants appear
green to us because they reflect rather
than absorb green light red and blue
light which plants absorb have the
greatest effect on plant growth there
are peaks in the red and blue
wavelengths where photosynthetic
activity is higher blue light is
responsible primarily for vegetative
growth when blue light alone is supplied
to plants growth is shorter hard and
dark in color the proportion of red
light relative to the amount
a far red light which is referred to as
the red to far-red ratio influences stem
elongation particularly in full Sun
crops when plants are grown in red light
growth is soft and the inter nodes are
long resulting in tall plants red light
when combined with blue light promotes
flowering plants adapt their growth to
try to position their stems and leaves
so that they receive more desirable
light conditions plants have different
kinds of receptors that perceive light
quality or the colors of light to which
they are exposed one of these receptors
is phytochrome which is sensitive to the
amount of red light relative to the
amount of far red light the ratio of red
to far red light also controls flowering
in plants that are sensitive to day
length plants that grow best under high
light or the full Sun are more
responsive to changes in the ratio of
red to far red light than plants that
tolerate low light being in the shade
spectral radiometer x' are used to
measure light quality these instruments
can cost four thousand dollars or more
greenhouse growers don't usually need to
measure light quality because it's
relatively fixed for each light source
whether it be natural sunlight or
artificial light from lamps the
distribution of light and the red to
far-red ratio varies between light
sources knowing these values can be
useful to predict the impact of
different light sources on plant growth
the large amount of far-red light
emitted from incandescent lamps in their
low lamp efficiency illustrate some of
the undesirable attributes of these
lamps the following chart shows not only
the differences in light quality based
on light sources but it also clearly
indicates how one light source may have
drastically different effects on
different plants
look for future videos to learn more
about light quantity daily light
integral and supplemental lighting
you