PAR light and Nanometers are commonly misunderstood in relation to horticulture.
The basic concept with PAR light is that plants only really need the peaks of
photosynthesis, or just the range of visible light that spans 400 and 700nm
range (approx.) Nanometers are a measurement that scientists made up to
explain what they were seeing. The word nanometer literally refers to one
billionth of a meter. Before that it was an Angstrom, and a millimicron, etc.
In science, references for references are often found to be flawed. Both of these
terms (PAR and Nanometers) are man-made, and therefore subject to the
knowledge and interpretation of those who made it. Plants just want what the
Sun has provided them for millions of years, what they need for their life processes. Humans cant selectively break the light that shines on the Earth into
just what falls into a visible range. There are portions of Sunlight that we dont
see with our eyes, but that plants use in their own way. The plant efficiency
curve was historically used in horticulture, but is really for humans more than it
ever was for plants. People cant cherry-pick the light from the Sun and nature
doesnt have two brick walls that say 400 and 700 nanometers.
The plant sensitivity curve represents the traditional basis for PAR light. The idea
is that peaks of red and blues are enough for proper plant development. Plants
want the Sun. Plants use all the light that they get from the Sun to make
chlorophyll a and b, and provide the electron volts to the light harvesting
complexes in the leaf; aka Photosystem 1 and Photosystem 2.
Light is a complex subject; light, light delivery, spectrum, frequency, and then
the photobiology, plant science, quantum physics and more. The complexities of
these disciplines only permit short explanation. Plants want the Sun, but the
Sun is twice the energy they need for maximum photosynthesis. Too much
light, too much heat, and too much humidity all inhibit the photosynthetic
process aka photo-inhibition. Light has properties of wavelengths, and long
wavelengths wave physics and particle physics are a part of that. Each color
of light travels at its own speed, each carrying a certain number of electron
volts; theres more than one speed of light. Plants want all the colors all the
time.
The relationship between frequency and wavelength are inversely related. The Sun is shining with full spectrum light, at a specific frequency. Higher frequency
electronics produce light thats closer to the Sun, but that man cant perfectly
replicate. The Sun shines in space in the Penta and Terra Hertz, but not all that
is received on the Earth PAR light is an expression for the visible spectrum, but
is no reference for what plants want. Plants just care about the incident energy,
the electron volts, that can actually be delivered to the leaf, that the plant can
actually assimilate for photosynthesis. Photosynthesis, for example, will stop on
the leaf surface when Sunlight levels reach approx. 6500 FC. More light isnt
always better. The Sun puts out approx. 10,000 FC; twice what they require for
maximum photosynthesis. Plants have just adapted to those excess levels of
natural Sunlight, to become the plants we see in Nature now.
