Hi, I’m Al Gracian from albopepper.com.
Today's grow light market is advancing faster
than ever before, especially in the field of LEDs.
New models hit the market every month.
Lights become more efficient AND more affordable.
But the selection process is becoming more
complex as well.
We must filter out over-inflated product claims.
Meanwhile, we're trying to understand the
various product specs and what these mean
for us.
What is PAR light?
Do plants benefit from full spectrum light
or is red & blue all that they use?
We'll answer this in this 1st video of a multi-part
series.
And then later, we'll get into PPF, PPFD and
light efficiency.
And finally we'll compare the pros and cons
of various light technologies and their form
factors.
When looking at the characteristics of a light
source, we can focus on two crucial aspects:
First, there is Light Intensity which refers
to how bright a light is.
This relates to the photon density.
(More on this in the next video.)
Secondly, there's Light Quality which is also important.
This refers to the composition of light.
How much red is emitted in relation to blues,
greens or any other color?
And that’s what we’re discussing today.
So lets start with the basics!
Grow lights emit radiation within the visible
light spectrum.
This chart, which you'll see time and again,
portrays a narrow portion of the electromagnetic
spectrum.
Each color has its own unique wavelength,
from violet to red.
A specific color can be described by its wavelength
in nanometers (nm).
So a blue light may be 450 nm while green
is 550 and red is 680.
Travelling left on this graph, towards blue,
each photon (or particle of light) has more
and more energy.
Moving right, towards red, each light wave
possesses less energy.
As you get right outside of the visible spectrum
(below 400 nm) you have Ultra-violet light.
Some grow lights may produce UV in addition
to visible light.
And interestingly, plants have shown physiological
responses to UV with improved disease and
pest resistance.
Between 710 and 850nm we have Far-red light,
which plants are sensitive to as well.
Far-red does less to drive photosynthesis,
but can greatly effect plant development or
morphology.
For example, certain ratios of red to far-red
can tell plants that they’re under a canopy
of taller plants, triggering them to grow
taller in response.
Of course, the most crucial range for plant
growth is within the 400 to 700nm color range.
Photons within this range are most effective
at driving photosynthesis.
This is referred to as PAR light (Photosynthetically
Active Radiation).
Note that this range includes even green light.
Wait a second!
Don't many growers emphasize blue and red
frequencies, saying plants don't use green
light?
They may refer to green as being completely
wasted light.
Well, for decades researchers have demonstrated
that green light serves a useful function
and is capable of driving photosynthesis.
In fact recent research is revealing some
unexpected benefits of green light, even helping
with organic pest control!
The point is, don't prescribe to the oversimplified
mentality that plants only need one or two
colors to thrive.
They may live and grow, but that doesn't mean
that all other light frequencies are useless
and unneeded.
But where did this misconception come from?
Well one thing that doesn’t help is the
misapplication of the photosynthesis absorption
spectra.
People love bringing up this little graph
which certainly makes green light APPEAR useless.
Even laying on that popular carotenoid graph
still leaves a big gap.
But how was this data gathered?
This is based on testing of thin algal solutions.
Higher plants (you know the stuff that we’re
trying to grow) do not respond to and process
light in the same fashion.
They have much more complex structures.
In reality, “green leaves of land plants
absorb a substantial fraction of green light.”
And this light then drives photosynthesis
as well.
So yes, plant leaves reflect SOME green light.
And that’s why they’re green.
That’s good because this results in improved
canopy penetration.
But ultimately, much of that light is able
to be harnessed.
Should that really surprise us though?
Afterall, the PAR measurements used by horticulturists
give green photons the same weight as blues
and reds.
So really a broad, full spectrum light source
is a good thing.
- not a bad thing.
A spectrometer can analyze a light source
revealing the ratios of one color compared
to another.
Many light manufacturers will share spectral
graphs of their light.
It may be portrayed as a curve like this or
perhaps this.
Plants respond differently to different combinations
or ratios of light.
At different phases of growth, certain spectrum
profiles may enhance results.
Professional growers may switch bulbs as their
plants mature and enter their fruiting or
reproductive phase.
High Pressure Sodium lights are heavier in
the yellow through red end of the spectrum.
Meanwhile, Metal Halide lamps emit a larger
amount of blue and UV.
You may be familiar with the Kelvin rating
system which is commonly used to describe
the color characteristic of Fluorescent lights.
Lower numbers like 2100 K have a warm amber
hue while "cooler bulbs" like 6500 K are higher
in blue light.
With the widespread adoption of LEDs, we do
see LEDs that use a Kelvin rating - but many
plant grow lights do not.
Instead, they may contain multiple diodes,
each of which emits a unique narrow band of
color.
A 3 band LED, for example, may contain 1 type
of blue and 2 types of red.
Thus, custom tuning of that "perfect" ratio
is often sought ought as one LED seller tries
to stand out from the rest.
LED Grow lights are showing more and more
color bands.
Some even claim to be "full spectrum".
This can be achieved by including a few diodes
that have a phosphor coating.
The coating changes the energy state of photons
from a blue diode.
The result is a mixture of wavelengths that
produce white light.
The reliance on phosphor coatings slightly
reduces an LED's efficiency rating.
But it creates a more rounded spectrum that
is likely to support a broad range of plant
types.
Light Quality can have a drastic impact on
plant development, effecting the shape and
length of plant leaves.
But just as important is the overall Light
Intensity.
What's the best way to measure light intensity
when it comes to plants?
Our next video will answer that question!
Thanks for watching.
Please subscribe if you haven’t already.
And as always, Happy Gardening!
