Light can be understood as a combination of
energy waves traveling outward from a source, or as
small packets moving from that source at the speed of light
(each peak in the traveling waves would correspond to a single packet
of energy, a photon). Light
always travels at the speed of light, altering only for
the material through which it's moving (it goes slower in
water, for instance), so a segment of a light beam with wave peaks
more separated (a longer wavelength) would
have fewer peaks absorbed by a surface (a lower frequency)
in any given amount of time, and would hit that surface with
less energy. This means
short wavelength = high
frequency = more energy, long wavelength = low
frequency = less energy. The only reason that
this is important is that sunlight
contains a fairly
range of energy frequencies, but only
a few are absorbed and
used by chlorophyll,
the energy-capturing molecule of photosynthesis.
can tell a few of the frequencies that are not
absorbed by chlorophyll (and a few other light-absorbing
molecules) by looking at a plant. That green you see
is part of the
reflected frequencies of
light. For the most part,
the other frequencies of light
is used in an energy conversion process that "spits" electrons
through a system from the "excited" chlorophyll
molecules. Energy conversion can
also involve reradiation - electrons on certain atoms will
absorb a particular frequency, "jump" to the next electron level
(which, with just one electron in it, will be unstable), then "jump"
back, releasing the energy at a different frequency (because some
has been used). Some radiation is called ionizing radiation
because it can make electrons jump completely off their atoms.
Although land plants absorb a variety of light frequencies,
all frequencies are not equally powerful or useful:
while plants can absorb both red frequencies and purple
frequencies, the purple have shorter wavelengths and carry
more energy. This is one of the reasons why
"plant lights" are distinctly purple.
It is not unusual
for land plants to use molecular supplements to
frequencies that chlorophyll can't, and feed more energy into
the photosynthesis process; these pigments
are commonly types of carotenoids.
of leaves in the autumn reveals the carotenoids that
have always been there but have been covered by huge amount
Carotenoids can serve multiple
roles: they can be photosynthetic aids, but they may
also minimize light damage (animals use pigments, like the
human tan-producing molecule melanin, for similar protection)
or even function in fighting disease. Land plants may
including carotenoids, in structure that need to stand out,
such as the colors of flowers or mature fruits. These colors
signal animals that a food bribe is available, and then the animals are used
to carry pollen or seeds.
Ranges of wavelengths associated with different types of energy.
Graph showing the many wavelengths in the sunlight that hits the
atmosphere, and the fraction of those that reach the surface.
The wavelengths absorbed by plant pigment molecules.
How does "visible light" fit in the full spectrum of radiation
A page on photosynthetic pigments.
A page specifically on carotenoids.
How autumn leaves get their color.
Pigment use in flowers.