Key takeaways
- Three separate trials put the gain between 10% and 30% more trimmed flower, and the most rigorous of them hit 20% without adding a single watt.
- Most of the money is in grade, not gross weight — B-grade popcorn converting to A-grade is what pays the fixture back.
- Switch the bars on once stretch has finished, around days 14 to 21 of flower, not before.
- Under canopy bars raise transpiration, so check your dehumidification headroom before you check your light budget.
- In a crowded, well-dialed room with a tight canopy, the return shrinks fast — this is not a universal upgrade.
The question we get about under canopy lighting is almost never "what is it" — it is "does it actually pay, or is it another bar of LEDs somebody will be explaining to a CFO next quarter." Fair question. What follows is the evidence rather than the pitch: what three separate trials measured, what growers report once the bars have been running a year, and the situations where we would tell a customer to leave the money in their pocket.
A spec-by-spec comparison of the fixtures themselves — PPF, efficacy, IP rating, daisy-chain limits, brand by brand — lives in our under canopy LED grow light comparison, and that is the better page for that job. This one is about whether to run them at all.
Recorded May 2025. Two things said on camera have been superseded since, and both are corrected in the article above. The 20% yield and 27% bud-ratio trial is StateHouse Holdings' multi-site study, not TSRgrow's own research. And the 5% potency figure traces to an older study — the 2023 multi-site work measured potency specifically and found no significant change. Fixture specifications read off the DLC listings were current at the time of recording; check the listing rather than the video before speccing anything.
Video transcript about 15 minutes
0:10Hey everyone, Nate from Canna Cribs. So today we're talking about under canopy lighting, because it is one of the hottest topics in cannabis cultivation at this moment in time. And if you're not using under canopy lighting in your cannabis grow and you're growing as a business, you're probably kind of falling behind. So let's chat about that a little bit.
0:26You know, if you're not using under canopy lighting, you could be losing yield to larger buds, and your competition could be pulling more weight and more A-grade colas — referring to those larger, more dense, potent buds that normally are only at the top of your plant, but you can be getting those in the middle and bottom of your plant. So they're doing that with the same amount of square footage.
0:52Under canopy really isn't the latest trend. It's becoming a necessity for a lot of growers who want to stay competitive and boost their yields per square foot and maximize the value of every plant they have in their facility. When building out new facilities or optimizing existing facilities, our Canna Cribs consulting team is now recommending under canopy for all building installations. As long as you have the budget for it, it makes a ton of sense on the front end.
1:21So let's go over why under canopy lighting is changing the game, and teach you some tips and tricks of how to shop for under canopy lighting, so that you know the difference between marketing hype and true performance of a light. But let's talk about the core benefits of under canopy lighting first. There are six of them.
1:36When we talk about under canopy lighting, we're really talking about unlocking yield that's already there in your plant. It's just kind of hiding in the shadows. Let's go over a few points that are really important to note.
1:47One, you can get more yield from your garden with the same footprint. So by illuminating the lower bud sites that are otherwise remaining shaded, the under canopy lighting unlocks basically this additional harvestable biomass. It supports higher grams per square foot without expanding the facility footprint — especially impactful for environments where expanding your footprint can be very costly.
2:11Two, boost in bud quality. A lot of your plant, what comes off of it, are these popcorn-like buds. With light reaching the lower branches, you're going to get more dense A-grade nugs, as I mentioned earlier.
2:22Three, full plant photosynthesis. Cannabis plants tend to stretch towards the light source, which can lead to elongated stems and less desirable bud structure. But providing light from below makes the plant grow a little bit more uniformly, and it reduces the need for the stretch, resulting in a sturdier, more desirable plant morphology.
2:38Four, labor saving. So cannabis growers usually trim, or prune, plants below the canopy. This lollipopping, as it's commonly known as, makes sense when you don't really have good bud formation down there on that bottom part of the plant, but it does take a lot of time. So with under canopy lighting, you can eliminate or vastly reduce the amount of time it takes for you to lollipop your plants, because you're going to get good bud formation down there.
3:02Five, air flow and microclimate friendly. So under canopy lights are slim and passively cooled bars, and they won't really block air flow or create heat pockets, as long as you have proper air flow in your room. Make sure to measure the air flow, the temperature and the humidity within your canopy before and after installing your lights, to see if fans need to be adjusted or added.
3:30Number six, decreasing pests and disease. This one's kind of crazy, but under canopy lighting actually deters some pests from hanging out in the shadowy areas of your plant. So the under canopy lighting also reduces the relative humidity in that area below the plant, which makes the area less hospitable to some pathogens and pests.
3:49Let's next talk about some data that supports some of these results. For example, a study highlighted by TSRgrow revealed a 20% increase in yield and a 27% enhancement in bud size when under canopy was utilized.
4:03Practical applications further support these findings. For instance, a performance test of California LightWorks' MegaDrive under canopy system reported a 29.84% increase in total dried trimmed flower and 11% rise in A-grade flowers at the Harborside greenhouse. Yes, a greenhouse, not an indoor facility.
4:24Similarly, this research conducted by Thrive Agritech indicated that integrating under canopy lighting led to a substantial increase in A-grade flowers — referring to the highest quality buds, versus B-buds, which are lower quality, less dense and less potent. Not only were there more buds, but they also exhibited an increase in cannabinoid and terpene profiles throughout the plant, accompanied by a notable 5% increase in THC levels across the crop. Now, we're going to link all these studies below so that you can click through and see them for yourself.
4:54Now let's talk about choosing the right fixture. Let's start about talking about how under canopy lights are measured. Usually it will be by wattage, spectrum, and efficiency of the lights measured by a term called micromoles per joule — µmol/J. You will see it often notated by that, and it basically measures how efficient a grow light turns electricity into usable light for your plants. The more µmol/J you have, the more light you're getting to your plant per watt of energy that you're paying for. Basically, more yield per watt that goes into your plants.
5:24For example, if a light is rated at 2 µmol/J and another one is rated at 3 µmol/J, then the light at 3 µmol/J is 50% more efficient at converting power wattage into plant growing light. It's kind of like miles per gallon in your car, but for grow lights and photosynthesis.
5:50Some companies will claim a certain amount of µmol/J, whether it's on their packaging or their advertising, but sometimes they might budge a little bit on that marketing rating to entice customers, to make them think that their light is actually maybe a little bit more efficient than it actually is. We're going to teach you how to be an informed buyer. Let's jump into that.
6:08First, there's a third-party organization called DLC, which stands for DesignLights Consortium. DLC is an independent organization that provides third-party testing and certification for LED grow lights, ensuring that they meet strict energy and performance standards. Their certification helps growers identify high-quality, reliable lighting products that may qualify for utility rebates. Let's jump over to the website really fast and I'll show you how to use it.
6:33Okay, so here's the DesignLights Consortium website. First thing you need to do is you need to make an account — you can't access the proper reporting without making an account. Then once you do that, click on Find Products and then go to Hort QPL. Once you click into Hort QPL, you can basically search any LED grow light that has ever been submitted to the DLC.
6:57And basically, if a light is from a well-known manufacturer and it's a light that you can get rebates from from, let's say, your local energy company, it probably is in the DLC. And I would even venture to say that I would be very reticent to buy a light that's not listed in the DLC, because that means that you probably don't have third-party reporting showing how efficient or non-efficient that light is.
7:29So if you first get into the DLC, how you search lights is just searching any light. So I can look up, for example, Grower's Choice LED lights — you know, another popular brand, we sell a lot of them. You can see the under canopy light and a few of their other lights.
7:46After you do that, you can start searching for fixtures. Like for example, we're talking about under canopy lights today. I jumped over and look — this is one of the most popular under canopy lights out there. This is the Craft Farmer light. And he was really someone who popularized under canopy lighting.
8:02And here's how you go through the website. First is reported photometric performance, then tested photometric performance. Reported photometric performance is what the company said their performance of the light is. So here is the µmol/J — 2.4 — and then it has total reported photosynthetic photon flux. And then if you look at this part down here, it'll actually show you the spectrum: 400 to 500 nanometers, 500 to 600, 700. So this is more blue light, 400 to 500, and 500 to 600 is more white light. And then 700 to 800 is really more far red. So I can see that this is a red dominant light — not so much a far red, but a red dominant one.
8:44Now what I can also do here is go to tested photometric performance, which actually shows, when the light was tested by a third party, what reports they got. So the reported was 2.4, but the tested is 2.5. That's actually really good. That means they report less than they actually tested at. What you really want to look for is when someone reports something like, let's say, they reported a 2.7 and actually tested in a 2.5. That means they are actually saying that the light is more efficient than it actually is.
9:19And you can see the spectrum here follows a very similar ratio as it does up here. So I would say that's very honest in terms of its output. And you can see there's other lights in here. Here's a California LightWorks under canopy light — this is a new one that came out with some new updated technology. It's at 3.22 µmol/J. And if you go down here to the tested photometric performance, you can see that they're tested at 3.204. So it's really spot-on. And you can look at the spectrum on this one: not really far reds here, but a deep, deep amount of reds in terms of the output.
10:00So that's how you can really use this website to drill in and understand what the third-party testing is of these specific lights. Now that we know how to use the DLC website, let's actually go over a couple other things, because, like everything in life, under canopy lighting is not perfect. There are certainly things to watch out for when using under canopy lighting.
10:15So number one, turning on the lights too early in your schedule. Don't use under canopy lighting during all phases of your plant's growth cycle. Like for example, do not use them in veg — it's wasted energy. You actually also do not need to use them in early flower. The ideal time to turn them on is usually about 14 to 21 days into flower, after your plants have gotten through their initial stretch.
10:39Two, heat buildup under the canopy. So when you add more power into your grow rooms, you will also add more heat. Ensure that you have enough HVAC to withstand the added heat load. When the canopy is full, the crop will likely have higher overall transpiration rates with the addition of under canopy lights, so this might also increase the humidity load. Make sure you have adequate dehumidification, and also make sure that you have good air flow throughout your rooms. If you have stagnant air under the canopy, you could see some heat stress on your plants. So make sure that you get some air flow down there and monitor your temps at the canopy bottom.
11:21Three, placement of them. So poor placement can cost you. Really make sure you place your under canopy lights in the proper spot, where they should be pointing up at your plants, and usually about 8 to 12 inches below the canopy where those leaves are. And normally you'll see them on stands. Stands are highly recommended, and then you can adjust them to the right height.
11:44Number four, matching the spectrum to your plants. So this one — while we don't have a ton of data on this — it's kind of recommended that you try to match the spectrum of your top lights, so you don't confuse your plant's photoreceptors. So light spectrum guides plant development, and conflicting signals, some people think, can stress out a plant or reduce the efficiency of your lighting. If your top lights are full spectrum, we kind of recommend getting a full spectrum under canopy light, or at least one where that's not a super deep red and only reds. If your top lights have red enhanced diodes though, then maybe you can use something that does have a deeper amount of reds for your under canopy lighting.
12:23Lastly, let's run through some products, because there is no one-size-fits-all with under canopy lighting. Let's break them down in terms of power, spectrum, unique features, and which light might be best suited for you. We did build a blog post that is linked below on our site, and it has a chart that shows every under canopy that we sell — and we sell the majority of them.
12:47Each light does have their own specifications that make them either more powerful, more efficient, or better suited for certain facilities. As I said earlier, there's no one light that's best for everyone, but there is probably one that's best for your operation and your budget. iLuminar has the most powerful 4 ft under canopy bar that we know of at 160 W, because most of them were designed to be 120 watts per bar. The California LightWorks has their patented MegaDrive, and it makes it easy to daisy chain hundreds of fixtures and run them at any voltage from 120 to 480 volt. And there's companies like FloraFlex that are offering right now the most efficient LEDs at 3.3 µmol/J, as of recording this in about May of 2025.
13:23If you want to dig a little bit more into our options and offerings, click on that link below in the blog and you'll be able to go through all the features and specifications at your own pace. If you're thinking about buying under canopy lighting and you would like some assistance, please reach out to our team at growershouse.com. We can set you up, make sure that you're successful with under canopy lighting, which is the most important part, because it is an investment. And if you want to get rebates under canopy lights, we can help out with that too. We've actually done full installations of under canopy lighting where in some places the rebate paid for the under canopy lighting 100%.
14:03In close, if you're growing in a cannabis facility as a business and trying to be as good as you possibly can, under canopy lighting is no longer really optional. It's part of your competitive edge. So no matter the size of your grow, there's a fixture that fits your needs. And like I said earlier, check out the full lineup on growershouse.com and one of our consultants would be happy to get you dialed in. So grow smarter, light deeper, and harvest better. Over and out, my friends.
Under canopy, inter canopy, and the larfy lower third
A top light throws photons down onto a canopy that is very good at absorbing them. By the time light reaches the third node from the bottom it has been through four or five leaf layers and there is almost nothing left. The plant knows it, and it stops investing there. What you harvest off those sites is larf.
Under canopy lighting — sometimes called subcanopy lighting — puts thin LED grow light bars below the canopy, on the bench or the floor or on stands, firing upward into that shaded zone. Inter canopy lighting is the related idea with the fixtures pushed into the plant, among the branches. David Hawley, Principal Scientist at Fluence, draws the distinction by plant spacing: widely spaced plants have room for bars between them, while high-density benches do not, which is why most North American rooms end up subcanopy. On the four-foot tables that dominate US facilities, Fluence measured subcanopy placement outperforming inter canopy by an average of 7.1%.
That is the whole mechanism. You are not adding growing space and you are not, if you do it the way the best trial did it, necessarily adding power. You are moving photons from a place where they are being wasted to a place where they are not.
Does under canopy lighting work?
Three sources have put real numbers behind this, and they were run by different people with different equipment in different rooms. That is what makes them worth reading together — they are not three versions of one press release.
California LightWorks ran a MegaDrive UnderCanopy test at the Harborside/StateHouse facility in Salinas, California, on Oreo Cookies, over an eight-week run in October and November. The control block had top light only at roughly 500 µmol. The test block added 40 of the 120-watt bars, two rows of twenty, 2.5 feet apart and 16 inches above the bench, running the same 12 hours as the flower lights. Total dried, trimmed medicinal flower came in 29.84% above the control, and the share graded A rose by 11%. A second test at the same site landed near 30% again.
The 2023 StateHouse Holdings validation study is the most persuasive of the three, because of how it was designed. Run across three facilities with different cultivars, environments and flowering times, with cultivars randomized between treatments, it was overseen by a research coalition led by Dr. Allison Justice using Grow Light Design fixtures. The trick was that the intercanopy treatment did not get extra energy — roughly 30% of the existing daily light integral was simply redirected downward. Same total photons, different address.
A 20% average increase in medicinal flower yield and a 27% improvement in the premium-to-small flower ratio, with no additional energy use and no significant change in potency.StateHouse Holdings multi-site study, June–September 2023
Thrive Agritech comes at it commercially. Their under canopy program carries a published guarantee of a 10% yield increase and full payback inside the first harvest, and their own case figures put the gain at 8 grams per square foot of premium product — about $37,000 a harvest at the $2.20 per gram they assume. That is a manufacturer's number rather than an independent one, and it belongs at the optimistic end of the range. It is still the only one of the three that comes with a guarantee attached.
| Source | Design | Yield result | Quality result | Extra power? |
|---|---|---|---|---|
| California LightWorks · Harborside/StateHouse, Salinas | Single site, 8 weeks, 40 bars vs top-light control | +29.84% dried trimmed flower | +11% A-grade share | Yes — 240 W per 5×5 section |
| StateHouse Holdings validation study, 2023 | Three sites, randomized cultivars, equal total light energy | +20% average | +27% premium-to-small ratio; potency unchanged | No — ~30% of DLI redirected |
| Thrive Agritech (manufacturer) | Commercial program with a published guarantee | +10% guaranteed; 8 g/sq ft claimed | Premium grade, figure not broken out | Yes |
Read the right column and the argument gets sharper. The trial that added no power still returned 20%, which means a meaningful share of the gain is not about more light at all — it is about where the light lands. If you want the underlying arithmetic on how photons accumulate over a day, our guide to daily light integral covers it properly.
Grower testimonials and real-world outcomes
Growers who add under canopy lighting tend to describe it as one of the simpler ways to improve a harvest. Here is what cultivators and consultants have told us to expect, grouped by the thing they mention first.
Higher yields and better quality. The consistent report is a real weight gain alongside a real grade gain across every square foot of canopy. Thrive Agritech's own program figures put that at around 8 grams per square foot of premium medicinal flower; in commercial rooms more generally, growers describe flower weight rising by something in the 10% to 30% band while the popcorn that used to form at the bottom of the plant largely stops forming. Biomass that was going into trim goes into marketable colas instead. The share of the crop that grades premium moves with it.
Full plant development and uniformity. Growers report the lower branches catching up with the upper ones rather than trailing them all cycle. One consultant put it as getting A-grade nugs the whole way down and no longer needing a bag for popcorn. Plants lit from underneath also tend to come out shorter and sturdier, because they are not stretching in search of light. The 2023 multi-site study saw the same thing — slightly shorter plants, more uniform growth — and, worth noting, found no significant change in potency either way.
Labor and efficiency gains. This is the benefit nobody expects and everybody keeps. Lower nodes that never develop have to be lollipopped off, and that is hours of skilled labor per room per cycle. When those sites actually produce, growers tell us trimming time drops, and in a large facility that lands straight on the cost line. Most under canopy bars are slim passive-cooled fixtures with no fans of their own, so they slot through a canopy without blocking the air movement you already have. Several growers also report lower humidity and less pest pressure in the zone under the leaves, on the reasoning that a lit, drier space under the plant is a less hospitable one for mold.
The overall tone from people running these is positive, and consistently so. It improves yield and grade while making the crop easier to manage rather than harder. One cultivation director described under canopy LED as having become table stakes for anyone trying to get everything a square foot can give. The technology is past the experimental stage and the results repeat.
Where under canopy lighting does not pay
Every article on this subject quotes the same three trials and stops. That is not the whole picture, and if you are the one signing the invoice you should hear the other half from us rather than from a forum thread six weeks after installation.
A tight canopy fights you. Growers running high plant counts report that adding bars underneath crowds the bench further, and crowding creates more de-leafing work rather than less — which defeats the labor argument the fixtures were bought on. The tighter your spacing, the harder it is to get a bar where it needs to be.
You are adding transpiration, not just light. More light on lower leaves means more water moving through the plant. Fluence is explicit about this: intensity increases raise the moisture load your environment has to remove, and rooms that were already at the edge of their dehumidification capacity will find that edge quickly. Check your dehumidification headroom before you check your lighting budget, and be honest about whether your HVAC has anything left to give. This is the single most common way an under canopy install disappoints, and it usually shows up as a humidity control problem rather than a lighting one.
Diminishing returns are real in a dialed room. The trials compared under canopy lighting against top light alone. If your room is already at PPFD saturation up top, with CO2 enrichment and good training keeping the lower sites productive, you are starting from a higher baseline and the delta shrinks. Some experienced growers say plainly that they tested side and under lighting and would not do it again. Others argue that better canopy management — trellising and training the plant so existing light reaches further down — gets part of the way there for the cost of labor rather than capital.
Red-heavy spectrum can bleach. Bloom-weighted bars sit inches from tissue that has spent the whole cycle in shade. Fluence recommends a broad, balanced spectrum for exactly this reason — too much red at close range photo-bleaches. If you are running a red-heavy bar, that is an argument for starting dimmed.
None of this makes the trials wrong. It makes them conditional. The honest version is that under canopy lighting pays best in a room with a moderately open canopy, dehumidification headroom to spare, and a meaningful spread between A-grade and B-grade pricing.
Are under canopy lights worth it? Run your own payback
The published payback claims range from "one to two harvests" to "the first harvest," and both are defensible with the right assumptions. Rather than repeat either, here is the arithmetic so you can substitute your own numbers, because the answer swings hard on the last one.
California LightWorks published theirs, which makes it a usable worked example. A 5×5 canopy section producing 1.5 pounds gains 0.45 pounds at a 30% lift. At the $800 per pound wholesale they assume, that is $360 in extra revenue per harvest from that section. Two 120-watt bars cover it. With bars in this category running roughly $125 to $230 each, one section's incremental revenue covers its own fixtures inside one to two cycles — before any utility rebate, which on DLC-listed fixtures can halve the remaining time.
Working it out for your own room
- Take your current dried, trimmed yield for one bench section, in pounds.
- Apply a lift you actually believe. Use 10% as the conservative case and 20% as the realistic one — 30% is the ceiling a single well-run greenhouse trial hit, not a planning figure.
- Multiply by your real wholesale price, not last year's.
- Now do it again, splitting the gain between A-grade and B-grade at your own price spread. This is usually the bigger number, and it is the one most people forget.
- Count the fixtures that section needs, add cords and stands, and divide.
- Subtract the annual cost of the added watts, and add back the lollipopping and trimming hours you stop paying for.
Step four is where the decision usually turns. Fluence's read is that the financial benefit comes primarily from improved uniformity — fewer C-grade, more premium — rather than from dramatic yield multiplication. If your A-grade and B-grade prices are close together, under canopy lighting is a much weaker proposition than the yield headlines suggest. If the spread is wide, it is a much stronger one, and the 27% shift in premium-to-small ratio from the 2023 study is the number to model against.
When to turn under canopy lights on
Switch them on when stretch has finished and the plant has decided on its architecture — in most rooms that falls between day 14 and day 21 of flower.
Earlier than that and you are spending energy on a plant that is still reaching upward, and you can encourage the lower growth to run rather than to set. Later and you have given away weeks of bulking on the sites you installed the bars to fix. The Salinas trial ran its bars on the same 12-hour flower schedule as the top light, which is the sensible default: same photoperiod, same timer channel, no separate schedule to get wrong.
Two variations worth knowing. In a light-dep greenhouse the bars come on during the day while the blackout is open, not on a clock of their own. And if energy cost is the binding constraint, some growers run the bars only through the bulking window rather than the whole of flower — you give up some of the gain, but the marginal weeks late in flower are the least productive ones.
Height, spacing, dimming and the air underneath
The fixtures are the easy part. Getting them positioned, dimmed and drained correctly is what separates an install that returns 20% from one that returns almost nothing and adds a mold problem.
Height. The Salinas trial used 16 inches above the bench, and 12 to 18 inches above the medium is the range most manufacturers land on. What you are aiming at is the underside of the lower foliage, so set the height by looking at the plant rather than by measuring the stand. Adjustable stands earn their money here, because the right height on week three is rarely the right height on week seven; a fixed stand pair is cheaper and fine if your cultivars are consistent. Angled or tiltable bars help you land the beam where the growth actually is.
Spacing. Follow the manufacturer's footprint and overlap slightly rather than butting the edges together. A four-foot bar covers roughly four square feet of canopy beneath it. On a dense bench or a wide plant, two bars per row beats one bar working too hard. Where floor space is tight, stakes and trellis poles give you a mounting point the bench does not.
Dimming. Almost every serious under canopy bar is 0-10V dimmable, and that is not a luxury feature here. Tissue that has been shaded all cycle should not meet full intensity on day one. Start at 50% to 70% for the first few days and step up as the leaves respond — upward leaf movement is the signal you want. If you are running the bars off the same lighting controller as your top light, set the channel separately.
Measure what you changed. Take temperature and humidity readings at mid-canopy before you install and again after, at the same point in the cycle, so you have a comparison rather than an impression. Light is worth measuring too — a PAR meter held under the leaf tells you what the lower sites are actually receiving, which no spec sheet can. The rest of the meters and sensors category covers pH, EC and the environmental probes that go with them. If you find a warm pocket, another inline fan usually fixes it before more cooling does.
Water and cabling. Anything sitting at pot height gets irrigated on eventually. IP66 is the floor for a bar in this position, and IP67 quick-connects on the jumpers matter as much as the rating on the fixture body — a sealed light on an unsealed cord is an unsealed system. Keep runs tidy and off the floor where you can; interconnecting cords rated to IP65, daisy-chain cables and short jumper leads are all cheaper than a service call. Wipe the lenses down between cycles with the power off, and most sealed bars will take a gentle hose or pressure wash.
What to look for in a fixture
Once the decision is made, the fixture choice is a shorter conversation than most people expect, because the category has converged. Almost everything serious is a 120-watt bar somewhere between 2.5 and 3.3 µmol/J, and the differences that matter are in mounting, sealing and how many you can chain.
Efficacy still sets the ceiling. The Grower's Choice under canopy bar is a useful benchmark at 371 µmol/s and 3.07 µmol/J with an IP66 body and 0-10V dimming, listed at $179 — and the rest of the Grower's Choice range gives you a matching top light if you want one supplier. Spectrum is the next fork: a red-weighted bar such as the Faven R6 at 60% red puts more weight on lower flower sites, while a white-based bar like the Craft Farmer V3 — 6500K with deep red and far-red on top — is easier on staff working under the bench and, per Fluence, carries less bleaching risk at close range. Match it to what your top light is already doing rather than picking in isolation — and if that top light is still HID rather than LED, sort the top of the room out before spending on the bottom of it.
Then the practical three. DLC listing is what makes a fixture rebate-eligible and is the fastest proxy for independently verified performance; UL or ETL is the safety credential you want on anything running in a wet zone; and five years is the warranty length commercial-grade bars generally carry — the Craft Farmer bar goes to seven. Mounting decides the rest. Standalone bars with integrated drivers suit retrofits and smaller rooms, and length matters more than people expect: the GrowPros dual-channel bar comes in an eight-foot version that covers a 4×8 bench with one fixture instead of two. Multi-bar rigs like the FloraFlex under canopy system put three or six 120-watt bars on one frame at 360 W or 720 W, covering 4×4 through 4×12 at 2.7 to 3.3 µmol/J. Remote-driver systems put the power supply outside the room entirely — the MegaDrive platform in the trial above runs up to 80 bars from a single drop at distances to 500 feet, which is what keeps the wiring bill on a large greenhouse install sane.
Wattage is the last variable and the least discussed. Most of this category sits at 120 W, but the iLuminar 160 W R-spectrum bar runs a third harder, which suits a tall plant with a deep shaded zone and is more than a short one needs. That same bar also comes as a 160 W full-spectrum version, which is the tidiest way to settle the spectrum question above — identical fixture, identical mounting, and you pick the diode mix that matches your top light rather than compromising on the hardware. The Gavita UCL 150 W sits between the two on power. Across those and the wider Gavita, FloraFlex and iLuminar ranges there is a bar for most bench layouts, and the differences that will actually bother you a year in are sealing and cable management rather than photons.
| Fixture | Watts | PPF | Efficacy | Spectrum | IP | From | Where it fits |
|---|---|---|---|---|---|---|---|
| GrowPros 4 ft / 8 ft | 125–300 W | ~325–350 µmol/s (4 ft) | ~2.8 µmol/J | Full +5% IR, or 80% deep red | IP65 | $125 | The 8 ft version covers a 4×8 bench on one fixture. DLC and ETL, so rebate-eligible |
| Faven R6 | 120 W | 340 µmol/s | 2.9 µmol/J | 60% red | IP66 | $169 | Bloom-weighted and sealed to IP66. Dims to 35%, which suits easing tissue in |
| Grower's Choice | 120 W | 371 µmol/s | 3.07 µmol/J | 3.0 red-heavy | IP66 | $179 | Best efficacy of the single 120 W bars, and IP66. The value benchmark |
| California LightWorks MegaDrive | 120 W | 350 µmol/s | 2.6 µmol/J | Deep-red enriched, fixed | IP66 | $189 | Large rooms only. Up to 80 bars per drop, 500 ft, driver outside the room. Quoted, not stocked off the shelf |
| iLuminar 160 W Full Spectrum | 160 W | 448–480 µmol/s | 2.8–3.0 µmol/J | Full + added yellow/green | IP65 | $193 | Most photons per bar. Pair with a full-spectrum top light; easiest to work under |
| Gavita UCL 150 W | 150 W | 450 µmol/s | 3.0 µmol/J | Broad white + blue | IP66 | $200 | The white option that still holds 3.0. Dims to 10%, IP66, five years |
| iLuminar 160 W R-Spectrum | 160 W | 448–480 µmol/s | 2.8–3.0 µmol/J | Red-rich | IP65 | $216 | Same bar as the row above with the red mix. Tall plants, deep shaded zone |
| FloraFlex 3-bar / 6-bar | 360 or 720 W | Not published | 2.7–3.3 µmol/J | Full, or far-red (Emerson) | IP65 | $219 | Highest efficacy at the top of its range. One frame covers 4×4 to 4×12. DLC and ETL |
| Craft Farmer V3 | 120 W | 336 µmol/s | 2.8 µmol/J | 6500K + deep red + far-red | IP66 | $229 | Seven-year warranty, the longest here, and IP66 |
Two honest gaps in that table. The Grower's Choice product page does not print a wattage — 120 W is what its own 371 µmol/s and 3.07 µmol/J give, and what the category copy says. FloraFlex publishes an efficacy range but no PPF figure, so its output per bar cannot be compared directly with the rest. Neither is a reason to avoid either fixture; both are reasons to ask us before you spec a whole room around one.
Sorted by price, the pattern is that efficacy does not track cost. The cheapest bar here and the most expensive sit within 0.1 µmol/J of each other, and the best single-bar efficacy is the third-cheapest row. What you are paying more for further down the table is sealing, warranty length, coverage per fixture, or a driver that lives outside the room — not photons.
For the head-to-head on all of these, with the full spec sheets, chaining limits and third-party test data laid out brand by brand, the comparison article linked at the top of this page goes deeper than this table does. Whichever way you go, start with a partial install. Put bars over two or three benches, keep an unlit control block, and measure before you commit the whole room.
Under canopy lighting FAQ
These are the questions that come up on the phone most often, answered the way we answer them on the phone.
Is under canopy lighting worth it?
In a room with an open enough canopy, dehumidification headroom and a real price gap between A-grade and B-grade medicinal flower, yes — the published trials put the gain between 10% and 30% and the payback between one and two harvests. In a crowded room already at its environmental limit, the return shrinks and the install gets harder. The grade spread is the number that decides it.
Does under canopy lighting increase yield?
Yes, in every published trial. California LightWorks measured 29.84% more dried trimmed medicinal flower at Salinas, the 2023 multi-site study measured a 20% average across three facilities, and Thrive Agritech guarantees 10%. The 2023 figure is the most conservative and the most rigorous, since it added no energy at all.
When should you turn on under canopy lighting?
Around days 14 to 21 of flower, once stretch has finished. Run them on the same 12-hour photoperiod as your top light. Switching them on during veg or very early flower spends energy without a return.
What results should you expect?
More weight per square foot, a higher premium-grade share as popcorn sites fill in, shorter and more uniform plants, and less lollipopping labor. Growers also report drier, less pest-friendly conditions under the leaf. What you should not expect is a potency change — the 2023 study looked specifically and found none.
Under canopy or inter canopy?
On standard four-foot benches, under canopy. Fluence measured subcanopy placement beating inter canopy by 7.1% on that layout, and bars on the floor are far easier to work around than bars threaded through the plant at harvest.
If your question is not here, call us. We will talk through your room, your grade spread and your dehumidification before anyone talks about fixtures, and if the answer is that under canopy lighting is not right for your setup this cycle, that is an answer we are happy to give. You can reach the team through our contact page or leave a comment below.