+++ title= "Plant Grow Lights Analysis" date= 2020-03-08 template= "page.html" +++
As part of the Four Corners Garden, I was tasked with identifying economical, ecological plant grow lights. First: A primer on the properties of lighting; next: a table breaking down the three options I identified; then: how the contenders perform in Team Four Corners' primary metrics of Utility, Price, & Ecology. And finally: the champion is decided.
Everyone has heard of photosynthesis - turning carbon dioxide & water to sugar and oxygen, by way of sunlight. It's how plants survive, store food, and release the oxygen we breath. But have you heard of photomorphogenesis?
What do we call a plant's growth & development under different sources and intensities of light? Photomorphogenesis. That was a gimme. Two key light receptors that shape a plant's morphogenesis are phytochromes and cryptochromes, which respond to red & far-red light or blue light, respectively. There are also receptors for ultraviolet light & many varieties of all these "photoreceptors".
What may have you scratching your head is that most of them aren't directly involved in photosynthesis -- they merely optimize the plant's growth. That includes getting the best sun for chloroplasts, but those green bois will get straight to work as soon as sun hits them. They don't need to be told what to do by no photoreceptor! If anything, cryptochromes only need to tell chloroplasts when to take a break and avoid "photooxidative damage" - sun burns.
Some plants need a good ten to twelve hours of sunlight per day -- close to full exposure. Others are happier with six to ten hours of sun; we call them wallflowers because they stick to the shadows. We typically measure the amount of light with luminous flux or "lumens"; that's a rating you will find on many lights. Do note that plants measure things a little differently; they can make use of light outside the spectrum visible to humans -- which is all we include in a light's lumen rating. So that spec may actually underrate the full radiant flux the light puts out for plants!
For our garden, we are assuming the Three Sisters want 5000-7500 lumens of light per day. Even on an overcast day, the sun will put out ~2500 lumens; therefore we have to make up almost 5000 lumens to keep lighting optimal for our plant growth.
The optimum lighting for plants emphasizes ultraviolet, royal blue, red, and far-red light. Remember the chloroplast, powerhouse of photosynthesis? They reflect green & yellow light, so those shades are useless to plants. Different stages of growth favor certain wavelengths, but no seedling will turn away from ultraviolet light -- best for growing full, juicy fruit -- just because its young. Have you ever tried giving candy to a baby? That's even easier than taking it.
The wavelengths of visible light are in the hundreds of nanometers, but frequently lights are rated by Kelvin or "K". Kelvin and wavelengths are not directly convertable, as a light at a certain Kelvin emits light among many wavelengths. The light will peak at a certain, known wavelength for a given Kelvin; but still emit visible light in a broad range around that wavelength.
Ultraviolet, royal blue, red, and far-red light corresponds to ~385, ~445, ~650, and ~740 nm wavelengths, respectively. Further, the Kelvin ratings that would peak at those wavelengths are ~7800, ~6750, ~4615, and ~4050 K.
Note that the three options given below are obviously just a small spectrum of what's available. I encourage the reader to do their own research and make the choice that best fits their needs.
|IP65 Flex Strip||Integrated T8 Fixture||Aluminum Star PCBs)|
|Bulb Type||LED||LED||Power LED|
|Fixture Type||Strip||Tube||Individual PCB|
|Wavelength||Red: 620-625 nm;|
Blue: 465-470 nm
|Unrated||UV: 380-390 nm;|
Royal Blue: 440-450 nm;
Deep Red: 640-660 nm;
Far Red: 740-745 nm.
|Temperature||Unrated||Cool White: 4100K;|
Daylight Duluxe: 6000K
|Power||12 V DC||120 V AC||1.44 - 4.0 V DC (varies by color)|
|Watts||19.2/4'||19/4'||Max 3 ea|
|Price||$14.62/4'||$9.95/4'||Starting $1.43 ea|
|Package||16.4'; no hardware included.||4' fixture; mounting hardware, series power connector, & hardwire power cable included.||Bought individually with bulk discounts.|
|Notes||High-Density option. Waterproof. Requires wiring power leads.||Series-mountable up to 20'. Requires wiring power leads.||Requires extensive wiring, heatsinks, and power conversion.|
|Batch per 8' Bed||1/2 red & 1/2 blue, providing 5760 lumens at 38.4 watts||2, providing 3800 lumens at 38 watts||64, providing 3200 lumens at 192 watts|
The quality of light produced is the number one consideration.
Two Flex Strips produce an impressive 5,760 lumens. Buying red & blue strips hits the most important sectors of the color spectrum.
Two T8 fixtures are not quite as impressive, only producing 3800 lumens. Furthermore, the 4100 K "Cool White" and 6000 K "Daylight Duluxe" temperatures are not as ideally situated in the color spectrum for plant growth.
As individual lights, it would take sixty-four Power LEDs to produce a third-place luminescence of 3200 lumens! That figure was surprising to me, considering they also draw the most power and, I would expect, are manufactured to the highest quality. The Power LEDs do have two benefits: First, they are precisely designed for certain wavelengths. With careful choices, we can maximise the amount of useable light for our plants, even if total light is less. Second,as individual mounts, you could exactly spotlight your plants, and leave the space in between unlit. Of course, if you plant very densely or move crops around year-to-year, second benefit is moot.
In luminescence, I find a draw between the Flex Strips and the Power LEDs. The Flex Strips have superior output, but the Power LEDs are finely tuned to our purposes.
To stay below the team's $4,000 budget, we forgo a greenhouse or other enclosure. Considering that would protect the lights as well as the plants, it makes mounting the lights a huge concern.
The Flex Strip is available with a waterproof silicon coating at no extra charge. Still, it's power and ground connections are exposed and must be wired, exposing a vulnerability to water damage.
The T8 Fixture has a housing, but it's unclear how much protection that would offer to the connections between the bulb and the fixture. Further, its power leads are also exposed -- but admittedly they are wires instead of soldering pads, so they might be a little tougher. One benefit of the T8 is the series connection that allows up to 20' of continuous lighting from a single source.
By far the worst contender are the Aluminum Star PCBs. As individual components, each LED must be soldered to the next -- besides being mounted on a heatsink and put in a custom housing. While that's a fun project for a committed professional, our Garden is aiming for accessibility and modularity, making custom wiring a bad match.
For mounting, I declare a draw between the Flex Strip and the T8 Fixture. Both would be fairly easy to mount on cross-beams, but require extra waterproofing around leads and connections. The Power LEDs require too much wiring and protection.
Both the energy and financial economies of our lighting choice are cruicial. To be practical and adaptable for any overworked wage slave plucked off the street, the bottom line has to balance out. Besides the sticker price, lights having a large power draw requires more batteries and solar panels to support them.
The Flex Strip and T8 Fixture are almost matched for power draw, consuming 38.4 and 38.0 watts/hr, respectively. However, the Flex Strip is about 45% more expensive at $14.62/4'; that is when buying the longest reel, 16.4', and cutting it (yes, you can cut it! But only between every three LEDs!) into sections 'about' 4' long.
At the starting prices, sixty-four Power LEDs could cost $91.52! The actual price would come down due to buying in bulk - but for a personal project, Power LEDs will always be more expensive than the other options considered. Furthermore, out batch consumes a stunning 192 watts.
From an economic perspective, the T8 fixture can't be beat and wins this category.
Unfortunately, I am not versed in complete life-cycle analysis. For ecological impact I can only call it a draw, as all options are long-lasting LEDs.
However, I will say that the housing on the T8 fixture is unneeded if we are building our own mounts as assumed, so wasteful; and for the Power LEDs, the materials and waste an individual would likely generate trying to wire & mount them represents an inefficiency that a factory-complete solution would avoid.
With one win and two draws, the T8 seems like the winner - but this is the Lighting analysis. That's why we devoted three sections to a physics lesson and compared the Luminescence of our options first. For offering red and blue wavelengths and competing extremely well in power, price, and mounting, we recommend the LED Flex Strips. :muscle: :bulb:
There are T8 tube guards out there in red and blue colors. However, these do not generate that light originally, but merely mask other colors outputted from the bulb to change the color. You would be wasting a huge amount of your energy with those bulb guards. You need colored phosphors to get the T8 to emit the right color, but those bulbs can cost $15 a pop.
The Power LEDs provide ideal luminescence, but are prohibitively technical and expensive, from both a energy and financial perspective.