Wednesday, February 14, 2018

Introducing the LED grow lights

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 


Eight Gate Farm NH said...

There's a lot of useful information here Mike, I'm going to bookmark it for future reference. Right now all I have is the T5 setups but want to expand with LEDs. Hope your foot is completely better soon!

Margaret said...

That is an amazing photo of all the colours on the LED's & I'm impressed by the frame that you built to accommodate the fixtures. I have read a couple of articles on using LED grow lights and it certainly seems to be the wave of the future. At $66 for your two fixtures, that is certainly not bad at all (and a lot less expensive than I would have expected), especially if they do end up being sufficient for the entire shelf.

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