Hello once again. I haven’t posted since I broke my foot last
fall. Lesson learned: watch where you walk when working a leaf
blower, because a broken foot takes a long and painful time to heal. The foot is working better now, spring is on
the way, it’s almost time for starting seeds, and I’ve got some new LED grow
lights to show off.
For years I’ve used a 4 foot
shoplight with 4 fluorescent bulbs to start seeds, and for years there have
been times when there were more seedlings than space under the lights. The workaround was to do a plant shuffle,
moving trays out to the cold frame, then moving them back inside if a frost was
imminent. Even with the extra trips
between house and coldframe there were times when I had to hold off starting
seeds until space opened up under the lights.
This year I knew I wanted another light unit to avoid those extra trips,
and I also want to raise some extra seedlings for friends and neighbors. I almost bought a shoplight at Lowes
when they had a really nice one on sale for $40, when a thought came to me: are
there LED grow lights available that can be used for starting seedlings?
LED growlights are relatively new but
are being adopted quickly by growers.
The beauty of the LED is that it can be manufactured to produce light in a relatively
narrow band of wavelength, or it can be made to produce a full spectrum of
light, and these different LED's can be combined in a light unit to produce virtually any kind of light. Some of the fancy units even allow the user
to control which lights in the unit are turned on. Since a plant’s use of light is weighted more
in the red and blue parts of the spectrum, an LED growlight can be tuned with a
selection of LED’s that produce light at the wavelengths that plants need the
most. In theory, an LED growlight with a
light output tuned to produce useful light should use less electricity than
other lights and still produce the same amount of growth.
Several years ago I made a post about
lights, and I’ll borrow some of the tables for this post. The ‘action spectrum’ of chlorophyll A and B
is strongest in the red and blue regions.
Which is a little weird because sunlight peaks right between the reds
and blues, where photosynthesis isn’t driven as strongly.
Of
course, there’s more to it than that, there's always more to it than that.
That action spectrum measures how effective a narrow wavelength band is
in driving photosynthesis, then adds it all together to make a chart. It doesn’t take a holistic view of how the
full light spectrum works together to grow a plant. There are auxiliary pigments that can capture
photons in that yellow/green region that chlorophyll doesn’t use and pass on
the energy to chlorophyll. There are
phytochromes that require UV and IR light in order to regulate growth and maintain
plant health. This graph gives a more
nuanced view of the total absorption spectrum of a plant, showing that the
entire spectrum is usable, but some wavelengths are more useful than others.
Bottom line, plants require all of
the spectrum produced by sunlight, they just don’t require it in the same
proportions that sunlight produces, and that’s where artificial lights can
improve on sunlight by making a greater proportion of light that is actually
useful to the plant.
I shopped for LED lights on Amazon. At the cheaper end of the offerings were
growlights made of square aluminum plates, about the thickness of a slice of
bread and a bit over a foot square, weighing not much over a pound. Most of these had an array of 225 LED lights
of 1/5 watt each (nearly all of these LED bulbs are made by the same
manufacturer), for a total of 45 watts. Each LED is in a cone-shaped depression for focusing.
From these small units there is a big
jump to the much more powerful fan-cooled units used by professional growers,
and not much in between. I was hoping
for a single unit that would take the place of a 4 foot shoplight, but nothing
like that was available, so I decided on 2 of these:
Most of this type of light unit that were available on Amazon had only red and blue LED’s, in a ratio roughly between 2:1 up to
4:1 (red to blue). After doing some
research, I chose a unit that has not only red and blues, but full spectrum
white, UV and IR. That should cover all
the bases. Although the potential output
is 45 watts, the unit’s actual energy consumption is more like 35 watts. Don’t
ask me why this is so, I don’t know.
My educated guess is that 2 of these
lights will take the place of a 4 foot shoplight with 4 bulbs. They
should use about half the electricity of the shoplight. The first thing I found out about them is that
these bulbs are pinpoints of very bright light.
If I look directly at them, I’ll have after images for several minutes. I got this photo by first pressing the
shutter on the camera halfway down while holding the camera directly over the
light, which freezes the aperture opening, then moving to an angle and taking
the shot. It's not floating in space, it's the same light as in the picture above.
Including shipping, the cost for 2
lights was $66, comparable to what I would pay for a new shoplight and 4 T8
bulbs. The manufacturer is
Growstar. I counted 144 red LED’s, 50
blues, 25 white full spectrum, 4 IR and 2 UV.
According to the maker, there are 2 different kinds of red LED’s at
slightly different wavelengths, but they all look the same to my eye.
I built a small frame from 1x2’s to
hold them. With eyescrews installed on
the top of the frame, the assembly can be raised and lowered with ropes, just
as with the shoplight. It’s much easier
than moving a shelf with trays on it up and down. You can see just how thin these lights are here.
For both the LED assembly and the shoplight,
reflectors were put on the back side of the shelf unit. If the LED’s work out, they will be used as
the go-to lighting unit. When I run out
of space under these lights, I’ll put new starts under the old shoplight. This picture shows both the LED assembly and
the shoplight on the shelf below it:
LED’s turned on. It looks like there is adequate light
coverage for 2 trays end to end, and I’m hoping for enough coverage for 3 or 4
trays side by side.
Looking up, comparing the new technology
to the old technology:
The grow chamber that will be
used, with a movable reflector installed on the front side.
I’ll
be starting onion and lettuce seeds shortly, and will find out soon enough if
these lights are effective or not. I
think they will be, but if they don’t do the job, another light can be added
with some modifications to the frame.
I’ll keep posting on the results.
Happy growing season, all
