There’s a lot of info out there that is probably really helpful but that i don’t actually understand. Like you need growlights because they have wavelengths that ordinary lights don’t have. But also that any light with about 65000k should be good so what i am wondering i guess is can i just use whatever floor lamp with a 24W CFL globe that has a colour temperature of 65000k. Or do i have to use a special growlight. If so what growlights do you guys use because when i search online i can only really see temu ads which i don’t want so i don’t know where to buy from and what’s reliable and on top of that, what is actually available in Australia… I’m a bit overwhelmed by all the different things that need to be considered… help…

So I've been seeing a lot of posts about grow lights and such and I thought I would throw together a basic guide. With winter in full swing in the Northern Hemisphere I thought it would be useful to give just some basic information to help when choosing grow lights for your plant babies. This is not intended to be a conclusive guide and I encourage anyone interested to look deeper or correct me on anything.

What to look for

When choosing a grow light the most important value is going to be the PPE of a bulb. This is the efficiency of the bulb at turning electrical energy into usable light energy. As energy prices increase this is really important and we should all try to be energy conscious. Higher numbers here are always better.

The second important value is Photon Flux or PPF. This gets a little complicated but in general you can think of it as the intensity. In general here, the higher this number, the more photons the light is going to put out. This gets tricky though, as it tells you how much but does not tell you how focused that light is. Some manufacturers list a PPFD which is a density measurement which is more useful, but how it's measured is a crap shoot and whether it's included at all is a toss up.

To sort the PPF/PPFD out you can use a simple rule of thumb. Look at the bulb and see what its shape is. If it is a standard globe shape its going to diffuse the light and spread it around. If its a cone shape or flat its going to focus the light. If PPF is the same on both bulbs, you can assume the density of the globe shaped one will be lower than the other. This really depends on your use. You have a meyer lemon you want to keep going? Get the focused one and shoot that on it. If you have typical pothos or medium-low light plants? Throw the globe one in a standard fixture and roll with it.

Wattage is the other big player here. Do not pay attention to the wattage broadcasted on the amazon listing. They will ALWAYS try to list the incandescent equivalent wattage. That does not matter as incandescents are all but dead. You want to know the actual wattage used. That 200 watt led light on amazon is not 200 W. It's a marketing gimmick to get you to think you are getting more bang for your buck. Any reputable grow light manufacturer will clearly list the actual watts used when running the light. Anyone trying to hide that information is trying to mislead you.

Some people find the PAR value to be useful but I don't think it's that important and is largely also a marketing thing. It stands for photosynthetically active radiation and is essentially how much of the light is actually useable by the plants. The problem with this value is many plants use different wavelengths for different things and what happens is manufacturers make a bulb with a super high PAR value and its that ugly blurple because that maximizes that value. However, plants just simply aren't that fine tuned and realistically they want a light close to the sun in spectrum. Which leads to my next paragraph.

The spectrum largely does not matter. You want a bit of all colors in there. Reputable grow lights will either tell you the spectrum of the light in nm or will show you a spectrograph. You want the peaks in the reds and blues but you also do not want to cut out the middle. The rise of cheap LED lights have lead to a plethora of goofy designs and these perfectly tuned "Blurple" lights. They work, but there is no proof they work better than a full spectrum grow light. And the draw backs, for me at least, greatly outweigh the possible benefit. I like to look at and show off my plants, and nothing kills the natural beauty of my plants than this intense epileptic blurple color.

Side note, many grow lights advertise full spectrum or daylight color. Do not be surprised if you get them home and they tend to skew red or blue. It happens and perceived color is hard to predict. I tend to enjoy red skewed ones as they feel warm. If you get one that you just don't like the color of just return it and try something else. Or use them for your cuttings in an area you aren't in. That's what my blurple lights are all used for... in my basement.

Parting Tips and Summary

Heres a few tips you may find useful.

1.) Amazon is full of crappy grow lights that will do little more than waste your money. Take every one of those FENKEY 200 WATT MASTER GROW LIGHT FULL SPECTRUM BLAST SUN GOD RAY MASTER products with a huge grain of salt. Look through the description and see what the actual values listed for the previously mentioned metrics. Compare those values with other manufacturers. If the values seem too good to be true they most likely are.

2.) Don't bother with built in timers. It's christmas and you can buy timers everywhere. A timer and a power strip is way more versatile and you don't lose your timer if the light fails. And they are dirt cheap.

3.) Grow lights can be really cheap but again, keep an eye out for ones that seem too cheap. Buy some clamp light fixtures and some bulbs and throw them in there. Do not buy the self contained all in one stuff if you can avoid it. Especially those long black skinny ones that seem to be really popular, their efficiency values are super low and the density is awful. Again, you want something you can replace if need be and not have to buy a new fixture. Once those burn out you have to throw the whole thing out. And they burn out fast because they are usually junk.

I hope this guide helps some of you out and feel free to correct or clarify on any of the topics. I love you all and hope you dudes have a wonderful holiday season filled with thriving plants.

TL;DR go back and read it.. its cold outside and there's nothing better to do anyway.

Hi, I am a seriously noob gardener.

I recently took a major interest in growing food, especially with the price increases and the disastrous state of U.S. ag right now.

All my plant growing is inside my apartment ( no balcony). I get 6 hours of sun through the window, but that's a very small space. I want to grow more things, but that means grow lights are needed. I have heard that LED lights are great for small-scale gardening: versatile, long-lasting, energy-efficient.........

My question is: what is a good brand?........

Where do I get them? .................

How do I know which bulbs are worth the money?.................

Are there cheaper alternatives that work as well?.............

Standard light bulbs ( like for an ordinary lamp) probably won't do it , if I understand right........

And if you use grow lights, what works for your setup and why?

Thank you for your advice.

I'm looking for a good quality LED grow light from Amazon. I'm somewhat on a budget so lower priced recommendations would be best.

There's so many options and as we all know, Amazon reviews can be both confusing and deceiving. I have no way to test the strength of the lights so I'm going mostly off user reviews for a good product. This will be my first time purchasing grow lights so I honestly don't even know what to look for. In the past I just used t5 bulbs but those get expensive with the fixture cost figured in.

I'm trying to use them for a relatively small area. Approximately 4'x2' area, all one level.

I’ve been making my own LED lights for many years now and thought I would share a brief overview of the process in case anyone is interested.

It is much cheaper, usually higher efficiency than commercial units, and extremely versatile for a wide range of applications. I’ve personally used them for vegetables, cannabis, microgreens, and aquariums but you can use them for practically any application.

I would recommend using a constant voltage driver and wiring in parallel for a safer output voltage but you can also use a constant current driver and wire in series if necessary.

Items needed:

• LED strips (I recommend Samsung or Bridgelux)

• LED driver (Meanwell, Delta, Wallwart for low power applications)

• AC cord

• Wago connectors and/or terminal blocks

• Waterproof Junction connector (easily connect AC cord to driver)

• 18AWG solid wire

• Thermal tape

• Potentiometer (for dimming on drivers with external dimming leads)

• Heatsink, Flat/Channel/Angle aluminum

You can generally get strips in 1’, 2’, or 4’ lengths. I typically use Samsung strips that contain LM281+, LM561C, or LM301B/LM301H diodes. They usually range in 150-200+ lumen/watt which is ultra efficient. Usually 1’ strips are 12v, 2’ are 24v, and 4’ are 48v. Make sure you buy a matching voltage driver. Bridgelux is another high efficiency LED manufacturer but their strips use a non traditional voltage (20v, 36v).

Lower kelvin (2700k-4000k) is going to appear more warm white and have more red in the spectrum, while higher kelvin (5000k-6500k) is going to appear more cool white and have more blue in the spectrum.

Some drivers have internal current/voltage dimmer pots (eg. Meanwell A type) which is very convenient and doesn’t require external potentiometer, however be warned that you can’t dim past 50%.

Other drivers likes Meanwells B type have + dim leads and require an external potentiometer. You can fully dim the current but voltage is not adjustable.

A/B type has both features.

Step 1: Wire AC cord to driver input side with waterproof junction connector

Step 2: Attach LED strips to heatsinks or flat/channel/angle aluminum with thermal tape

Step 3: Connect output +/- to either Wago connectors or terminal blocks

Step 4: Feed 18AWG solid from Wago/terminal blocks to corresponding +/- on LED strips.

To determine the quantity of strips needed for your use, look at the max ratings on the spec sheet.

For example I have 2’ strips (H influx L09 that use LM301B dioxides that are rated max 1.6A @ 48v. That means each strips is capable of 76.8w. They are rated at 192 lumen/watt efficiency so each 2’ strip can put out a max of 14,745 lumens.

If you run a strip close to its max rating, you will need proper heatsinking. However, if you run a strip at ~50% it will barely get warm to the touch.

Where I source my stuff:

• Arrow electronics (good for strips/drivers/cords in bulk)

• Digikey (strips)

• Mouser (drivers)

• Amazon (wire, connectors, tape, etc)

If you have any questions feel free. I tried to keep the post informative but somewhat brief. I am not an expert by any means, just a hobbyist and DIY enthusiast.

TY (:

I'm looking for recommendations for a 4ft long LED Grow light that I can use for up to 4 tomato plants in DWC.

While searching Amazon I found this Grow Light but I'm always skeptical about cheap grow lights on Amazon.

EDIT: My intention with this post is to provide beginners purchasing their first grow lights with what I think is the most efficient way to spend their money. I am not claiming that those who have previously purchased and used T5/T8 style lights are bad people who will have zero success growing anything. If you have purchased and use these lights I wish you the best. My point is that for those purchasing new grow lights I think there are much better options, for the same or very similar cost, that are more suitable for home gardeners growing different plants at the same time. I welcome comments that disagree and provide general reasoning outside of your own personal experience using a shop light.

TL;DR Don't buy T5/T8 "shop light" style LED grow lights and definitely don't buy the clip on wand/bendy style of LED grow lights. These lights can work (and even work well for specific setups) but there are now much better alternatives for a home gardener who wants to prepare a variety of different plants indoors in order to transplant for their summer garden.

The first light on my list was specifically selected as a better alternative to a pack of the common T5/T8 "shop" light style of grow lights for approximately the same cost ($45-$60). Compared to the shop lights it provides much more light energy, uses less electricity and perhaps most importantly: allows you to grow a variety of different plants that are different sizes as you don't have to keep it so close to your plants. You won't have to constantly adjust the height and will be far less likely to produce a bunch of leggy seedlings - it's far more forgiving in this respect. It also provides enough light to grow almost any plant through it's entire lifecycle so if you end up having to keep your plants indoors for longer (e.g a cold spring) you will have this flexibility - not so with the shop lights. The other options on my list generally provide increased efficiency and/or grow area but are obviously a bit pricier.

I recommend any of the following lights for approx. 2' x 2' - 3' x 5' grow areas. If you are growing in bigger areas I assume you know all this already and can make your own buying decisions:

1. Viparspectra P1000: Great entry level light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Currently USD $58.

2. Spider Farmer SF1000: Another great light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Slightly more efficient LED's than the Viparspectra P1000 above. Currently USD $90 or $76 for the version without a dimmer.

3. Spider Farmer SF2000: I personally have this light and really like it. Stated coverage is 2' x 4' or 3' x 5' (germination/initial seedling) but I think this latter value is a bit of a stretch. I would say max 2.5' x 4.5'. Currently USD $180.

4. Viparspectra P2000: Basically a larger version of the P1000. Great light if you need to cover a larger area, or just get two P1000's since they're on sale currently and work out cheaper. Currently USD $128.

Disclaimers:

• I'm by no means an expert - this is only my second year gardening and starting seeds indoors.

• Most of the supporting information I'm presenting is research done by others who are far more knowledgable than me. I have tried to balance supporting my arguments with keeping the post length reasonable but would be happy to provide additional support or make corrections if someone finds an error.

• I'm not sponsored by or affiliated with any of the manufacturers of the lights I recommend.

I found myself replying to the posts of so many new gardeners with this information so I thought I would make a post about it. As I mentioned above I don't consider myself an expert but my personality is such that I spent a lot of time nerding out about the science and literature behind grow lights and their effects on plant growth.

Light, Defined

Light is a way of transferring the energy into plants that they require to grow. This light energy is referred to as photons. For plant growth we are interested in the photons that fall within a certain wavelength range and we refer to this range as "Photosynthetically Active Radiation" (PAR).

Measuring Light

We measure the output from a light by measuring the number of photons that fall within the PAR range referenced above. This is usually measured in micro moles of photons - per square meter - per second (μmol/m²/s). The name for this value is often called the Photosynthetic Photon Flux Density (PPFD). If these two terms sound unnecessarily technical or complicated don't worry - all that's important is that you know that grow lights are measured by how much light energy they are providing to a specified area over a specified time period. Here is an example PPFD map (at 3 different heights) of a Viparspectra P1000 which I often recommend as a good light for a small area.

Since the area the light is designed to cover is 2' x 2', each square basically represents a 6" x 6" square area with the middle commonly getting more light energy than the outer/corner areas. Note that lowering the lights 4" from 16" to 12" above the plants makes a big difference - a 38% increase in light output. Generally lowering the light increases the light energy in the centre area but at the cost of decreasing the light spread and lowering the light energy towards the outer extents.

How Much Light Energy Do Plants Require?

Unsurprisingly the answer to this is: it depends. Some plants require more light than others and plants also require different amounts of light at different growing stages. There are resources provided with plant-specific information but in general:

• Plants in their seedling stage require less light than the same plants in their vegetative growth stage. Plants in their vegetative growth stage require less light than the same plants in their fruiting stage.

• Leafy greens generally require less light than fruiting plants/vegetables.

• Roberto Lopez, Ph.D., researcher at Purdue University, developed a thorough set of guidelines to recommend the average daily light integral (DLI) for most common plants. His research showed that in order to produce crops at a high quality, most plants require a minimum DLI of 12-20 mols/m2/day.

Important: It's important to note that we refer to the amount of light required by plants as their daily light integral (DLI). Emphasis on daily. I'm pointing this out because when we choose a grow light we will want to look at it's PPFD map, which shows how might light energy is transferred in:

micro moles per square meter per second

Again - when we look at the DLI of plants the amount of light they require is generally expressed as:

moles per square meter per day (24h)

Therefore we need to convert those PPFD values to ensure that our grow lights put out adequate light energy for the type of plants we want to grow and also enough light energy into an area that is large enough to cover the amount of plants we plan to grow. For example, it's not very useful having a light that provides high light intensity (lots of photons) but only covers a 1' x 1' area if our seedling trays and pots fill up an entire 2' x 4' shelf. Conversely it's just as useless to have a light that covers your full 2' x 4' shelf but doesn't provide enough light intensity.

How Long Should Grow Lights Be On For?

I found this specific topic to be the most esoteric with some information indication slightly different answers. For home gardening and vegetable growing I feel that it's safe to assume the following:

• Some plants are capable of handling 24hr light but some are not.

• Beyond a certain point, however, more light energy becomes wasteful as plants can only use so much until other things become a bottleneck for photosynthesis.

• We generally want more light-hours during seedling and vegetative states and then slightly fewer light-hours during the fruiting stage.

• Most research points to ~16-18 hours of light per day for seedling/vegetative and ~12-14 hours during fruiting.

The most important takeaway here is when we calculate the DLI that we want to give our plants, we need to make sure we use the number of hours above and not 24 hours as our light will not be on 24/7.

Calculations and Light Recommendations

Converting between PPFD (from our grow light) and DLI (amount of daily light energy our plants require) is relatively straightforward. There are 1,000,000 micro moles in 1 mole and 3600 seconds in 1 hour. Assuming our light is on a 16hr-on/ 8hr-off schedule and using the centre value in the 12" PPFD map above of 800 micro moles per square meter per second, we get the following DLI:

800 / 1,000,000 = 0.0008 moles per square meter per second
x 3600 seconds = 2.88 moles per square meter per hour
x16 hours = 46.08 moles per square meter per day

This is more than enough but this is also best case scenario - we're using the centre area with the highest output and with the light only 12" above the plants. If we work backwards to figure out the minimum PPFD we need from our light, based on the recommended minimum DLI of 20 moles per square meter per day:

20 x 1,000,000 = 20,000,000 micro moles per square meter per day
/ 16 hours of light on per day = 1,250,000 micro moles per square meter per hour
/ 3600 seconds ~ 350 micro moles per square meter per second.

So, we need a minimum of 350 in our light PPFD maps to grow our plants in their vegetative state and get them ready to transplant. Side note: for growing plants through fruiting, we want ~500 micro moles per square meter per second.

One of the biggest mistakes I see people make (and one I made initially as well) is not considering that different plants that were planted at different times are going to grow at different rates and some will be much taller than others. If you are a home gardener then you are likely not growing in a commercial environment where you a have a shelf of one crop that all germinate and grow at the same time/pace. You aren't going to be able to keep your light exactly 12" above all your different plants all the time. If your tomato plants are 6" taller than your pepper plants (very likely) and you place your light 12" above your tomatoes, the light is now 18" above your peppers. As we saw above, this makes a big difference. Therefore, you need some buffer. My goal is to have enough light, even at the corners, to provide at least 350 μmol/m²/s to my plants from 18" (preferably 24") above.

Now that I've explained my methodology I will go over some lights I recommend and some I specifically don't recommend. My recommendations are based on the assumption that you live in the northern hemisphere and have a shorter-than-ideal growing season, so your goal is to grow indoors for ~4-8 weeks before transplanting outside when the weather is warm enough.

I don't recommend the clip on wand/bendy style of LED grow lights, AKA:

None of these provide a PPFD map showing light output for obvious reasons. This is the first red flag of any grow light. They have nowhere near enough light to produce successful transplants - even when these are so close to your plants that you risk the heat burning their leaves. For most of these lights the PPFD is not even 200 when the light is basically touching the plant. At 12" you are lucky to get 100 and above that you are lucky to get 50. Totally useless beyond helping with seed germination and maybe supplementing small indoor house plants where they just sit right above them 24/7. Don't get conned by the product images on amazon showing utterly superfluous details about lumen output and the number/color of the LEDS. This is just there to make you think they actually put some thought into these lights.

I don't recommend T5/T8 "shop light" style LED grow lights, AKA:

I often see well-known youtubers recommending these while making the point that you don't have to spend a lot on grow lights. They hold one up and go on about how it was only $20 on sale at Home Depot - with the implication that you only need to spend $20 to grow seedlings indoors. Then they pan over to their grow shelf where they have at least 4 of them on one shelf sitting literally right on top of their seedling trays.

These lights are less useless than the clip-on ones above but they are still pretty useless and end up costing more than a proper grow light while being very limiting. Some actually do provide PPFD values though. Here are the PPFD values for one of the most popular versions of these lights (Barrina T5 Grow Lights) currently priced at $50 USD:

So at 7.87" above our plants we would get just over half of the minimum that they need to grow adequately. At 12" above the plants are getting less than half the minimums that we need and at 18-20" it's basically useless. Even worse: these are the values when the plant is directly (i.e lines up vertically) under the light. If your pot is 3" off to the side you wouldn't even get that amount of light energy. The cheapest grow light on the recommended list below is $8 more which is why these lights are a waste of your money and, more importantly, your time.

I recommend any of the following lights for small-ish (2' x 2' and 2' x 4') areas. If you are growing in bigger areas I assume you know all this already and can make your own buying decisions:

1. Viparspectra P1000: Great entry level light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Currently USD $58.

2. Spider Farmer SF1000: Another great light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Slightly more efficient LED's than the Viparspectra P1000 above. Currently USD $90 or $76 for the version without a dimmer.

3. Spider Farmer SF2000: I personally have this light and really like it. Stated coverage is 2' x 4' or 3' x 5' (germination/initial seedling) but I think this latter value is a bit of a stretch. I would say max 2' x 5'. Currently USD $180.

4. Viparspectra P2000: Basically a larger version of the P1000. Great light if you need to cover a larger area, or just get two P1000's since they're on sale currently and work out cheaper. Currently USD $128.

I recently went through a sudden and devastating breakup and am having to move suddenly with my jungle of house plants. Unfortunately this picture is only about half of them and while I'm doing my best to find a place with good light my options right now are limited. I've experienced so much loss already this year and I really can't take losing my plants too. If anyone has solutions that won't make me feel like I'm living in an illegal grow op in desperate for advice 😞

First I would love to pretext this by saying this is my first post! Hi I'm Chris, and I love this forum, and find it to be so educational as an enthusiast / hobbyist!

Right now, I'm drafting an Aeroponics garden. Being a student of science and somewhat Type-A, everything has to be meticulously tailored to meet efficiency, practicality, and cost demands/restrictions! In spirit of the sentiment, I researched different lighting options and chose to opt for an LED solution for lighting (Sorry HPS lovers!). My research on these lights indicated a few different things, and your opinions/experience on these matters are paramount to me!

0: Watts. Very often, growers/designers quantify the light given to their plant in terms of Watts, but what is actually important is how much PAR ( source ). Product A and Product B may both run at 400 Watts, but the PAR actually being delivered to your plant may vary for many different possible reasons, including the quality of the chips(LED's are chips, not bulbs!) or their lens angle.

1: Different LED's need to be mounted at different heights, relative to the plant, because there is an optimal light intensity during each stage of growth. plants at the vegetative stage like 35,000 - 70,000 lux, while plants at the flowering stage like 55,000 - 85,000 lux. This can be calibrated using a lux meter. - Edit, this is only an effective method for white light.

2: Plants grow more effectively when the visible light spectrum feeding it is calibrated specifically to match the McCree Curve ( Source ). For this reason, and the nature of LED lighting, it is important to have multi-band lights. Manufacturers will design their products so that panels will have, for example, 11 varieties of lights on the panel to calibrate the spectrum, then have a 12th variety of white light, to fill the empty ranges in the spectrum. It should also be noted that plants respond to light outside of the range of the McCree curve, so this model, even though modern and helpful IS NOT PERFECT. Adding UVA and UVB to your spectrum can further promote a healthy grow. Many lamps will come with UVA, but UVB is less common. Do not bother with UVC, as it does not naturally penetrate the atmosphere, plants do not use it.

3: If light is only reaching certain areas of the space that your plant is confined to, your plant will respond to this by growing itself to get as much light as it can! Having full coverage and penetration in your lighting solution is important so that your plant can flourish on its own terms. Using a lower beam angle( like 30^o) will deliver more PAR to your plants over the canopy, which is where you want to provide the most light, but without wide angles (like 60^o) present, you may not penetrate the canopy and reach other leaves that are just as important in keeping your plant healthy! Some experienced growers prefer multiple small lighting units over one large unit because it provides them with more flexibility when tailoring their lighting solution.

4: Do not be fooled by the Watt rating listed on the product. Even though the manufacturer may be selling you a product with 50 3-Watt chips, this does not mean your panel with draw 150 Watts and convert it to PAR. Most 3W LED's are driven at a current of 550mA to increase the lifespan of the light. This would translate to an Actual LED wattage of 82.5W. You can get a general idea of your cost per unit with

Wt = advertised wattage

A = current

Ct = total cost

Actual LED Wattage = Wa = Wt (A)

Cost / unit = Cu = Wa/ Ct

Keep in mind, I'm not simply posting this for your benefit with no consideration for myself. I strongly encourage critical thinking and POLITE commentary and will do my best to both respond to, and learn from you and your experiences! in a best case scenario, I'm wrong and there's a better way, but I sure hope not!

Feel free to also ask me any questions about any of the other components of in the system, or about myself!

Hail /hydro/

-edited for formatting -edited to add more information

What grow lights are people using. I have a few smaller house plants huddled by a window for the winter months, and I’m thinking it might be beneficial to add a small grow light to the area. Thoughts? Suggestions?

New to indoor planting and my friend asked me this question and I didn't know how to answer her.

I been looking into led and I don’t want to spend more than I have to for quality. Does anyone here have any knowledge about lights like the ROI-E720, VOLT FL1, Gavita pro 1700e, ion led 720w

I live in a house with little light so my indoor plants have never really thrived. I have tried grow lights in the past but found they didn’t actually work. I have done research, but when it comes to buying a good grow light there are so many misleading advertisements that straight up just lie about the light. It is also difficult finding a light that looks pleasing in my home (warm colours) etc. I’m not too worried about price as I understand quality generally will cost more, but I really need some suggestions for grow lights that you have actually noticed a difference with. Particularly looking at something for my Monstera Thai Constellation, which I want to put in this corner of my bathroom (maybe attach the light to the ceiling?)

Theory and tips on white LEDs and grow lights

last update: 8 July 2021

I wanted to try writing stuff a bit different so I used bullet points with short and direct statements. There's a bit of theory below but actual white light theory would require its own article due to the 40,000 character limit in a post.

• part of SAG's plant lighting guide

• Using a lux meter as a plant light meter -if you don't know the conversion value, use 70 lux = 1 umol/m2/sec for white LEDs

• Core Concepts in Horticulture Lighting Theory -there is theory here that might make some stuff on this post more understandable

Good paper and the basic definitions

• From physics to fixtures to food: current and potential LED efficacy -Must read. When I write "above paper" with a page number, this is it. Note that this paper covers a lot of 2020 LED efficiency numbers while also discussing maximum theoretical efficacy in this paper, and it can be easy to confuse the two.

• PAR -"photosynthetic active radiation" or light from 400-700 nm by standardized definition. PAR is what we measure, and not a unit of measurement. Saying "300 PAR" would be like saying "300 water".

• PPFD- "photosynthetic photon flux density" or light intensity at the point of measurement. The unit is umol/m2/sec (µmol m-2 s-1) or "micromoles per square meter per second". The close white light analogy is lux.

• PPF- "photosynthetic photon flux" or the total amount of 400-700 nm photons per second given off by an LED/grow light. The unit is umol/sec (µmol s-1) or "micromoles per second". The close white light analogy is lumens (e.g a 100 watt incandescent bulb (true or equivalent) puts out about 1600 lumens of light).

• PPE- "photosynthetic photon efficacy" or the amount of photons produced by a light source per amount of energy input. The unit is umol/joule (µmol j-1) or "micromoles per joule". The somewhat close(ish) white light analogy is LPW (lumens per watt). You will sometimes see PPE written as PPF/W.

• Efficiency is the ratio of useful work (e.g an LED is 50% efficient if half the consumed energy is radiated away as the light). Efficacy, as how I'm using it, is how well something works (e.g that white 50% efficient LED at CRI 80 has a luminous efficacy of around 160 lumens per watt, give or take a bit).

The ultimate efficacy limits of fixtures

"The upper limit of LED fixture efficacy is determined by the LED package efficacy multiplied by four factors inherent to all fixtures: current droop, thermal droop, driver (power supply) inefficiencies, and optical losses" -above paper, page 1

• To maximize an LED grow light's idealized efficacy, we want the LED current as low as possible (throw more LEDs at the problem as they become cheaper and underdrive them), keep them as cool as possible (a little airflow goes a long ways, maybe 2-10 times so), get the most efficient driver (you want to look up the efficiency by current level curves in the data sheet), and don't use lenses or a glass cover. But, by not using a cover means we lose ingress protection leaving exposed voltages so there are potential safety concerns, and exposing the LEDs directly to the environment can potentially lower their longevity and the grow light's longer term reliability.

• Current droop -The greater the current though an LED, the less efficient it becomes. This is one reason why medium power LEDs in large series/parallel arrays (e.g quantum boards^® ) have become common at least in the hobby community, and how COBs work by having a large series/parallel array of LEDs in a smaller common package. LED makers typical rate their LED at a "nominal" or "sorting" current that may be significantly lower than what the LED is actually being driven at in real life. The Samsung LM301H has their specs listed for 65 mA, but is rated for 200 mA continuous, for example.

• Thermal droop -The higher the temperature of the LED, the less efficient it becomes. LED data sheets typically give bin numbers for 25 degrees C (77 F) or 85 C (185 F), and most LEDs are specified to operate at 85-125 C. Higher temperatures also means that the LED degrades more quickly, particularly red LEDs. The difference between 25 C and 85 C is about a 5% efficiency loss for most LEDs. Some 125 C continuous rated red LEDs can take a >20% efficiency hit at 125 C. Higher temperatures will also degrade LEDs faster, and cheap light bulbs are going to run their cheap LEDs very hot. Don't buy the cheapest light bulbs if you want them to last- you get what you pay for.

• Driver (power supply) inefficiencies -Some low voltage DC drivers can hit about 98% efficiency depending on drive current. There are AC LED drivers on the market that can peak at 97% efficiency. Some Mean Well LED drivers can hit the mid 90s% efficient. Most of the AC LED drivers you find in products are going to be in the low 90s or upper 80's percent efficient, which can depend on specific LED current levels. Drivers with a lower power factor also contribute to greater inefficiencies. Cheap capacitors in cheap lights (particularly cheap light bulbs) is a major failure mode particularly with poor thermal management.

• Optical losses -Using secondary optics (i.e a lens) over an LED can focus the light so an LED grow light maker can post some impressive PPFD (intensity) numbers right below the light, but the PPF number (total light output) is going to drop, too. There will always be optical losses with a lens of perhaps 7-9%. This same loss applies to grow lights that have a glass/plastic/silicon cover over the LEDs for splash proofing the light. If you grow hydroponically, and a prone to splashing hydro nute solution around, it may be worth it to take this inefficiency hit to keep the salt solution away from the electronics. Electrical safety is another very important reason glass covers are used for the ingress protection they provide.

Keep in mind on LED grow light specs, some low end sellers may give specs (e.g PPF umol/sec numbers) for data sheet temperature and current ideal efficacy (i.e 25 C, lower nominal current), or may not take in to account LED driver losses when posting a umol/joule number, and not how the light actually performs in real world grow conditions. If low end Amazon/eBay style lights are giving specs better than high end lights, then don't don't do business with that seller.

Some basic facts on LEDs, light, and lights

• The "K" in "color temperature" stands for "degrees Kelvin", not to mean "thousand". For example, it's a 2700K light, not a 2.7K light which is deep outer space cold. It's also a correlated color temperature (CCT), and not an actual approximate black body radiator color temperature like with a 2700-2800K incandescent light bulb.

• I define "white" as any light source whose spectral output is on or fairly close to the plankian locus in the CIE 1931 color space chromaticity diagram within a certain color temperature range (2700k-6500K or so). There are many types of white light (i.e different CCT, CRI, TM-30-15 Rf, spectral power distributions), and many ways to create white, so my definition is a bit vague. Bridgelux has 1750K LEDs they call white, for example, but I certainly don't perceive them as white.

• White LEDs (blue LEDs with a phosphor(s) for this discussion) are mass produced very well beyond any other LED lighting, which can make them cheaper through scale of economy, particularly the surface mount medium power LEDs like by Samsung. The amount of R&D into LED technology has resulted in some white LEDs having a PPE of greater than 3 uMol/joule at nominal (lower) current levels and at room temperature. They will max out at about 3.3-3.4ish uMol/joule depending on CCT and CRI, maybe slightly higher if underdriven.

• A 450 nm blue LED will likely have a maximum practical PPE of about 3.5-3.6 umol/joule, with a maximum theoretical PPE of 3.76 umol/joule. The 3.76 umol/joule number is the ultimate barrier to white LEDs based off a 450 nm blue LED with a phosphor, and the only current way to get a higher PPE for grow lights is to add actual red LEDs to white LEDs, or if appropriate for your plant, use red and blue LEDs only (perhaps with some white thrown in).

• There are white LEDs that use the phosphor pump from violet or ultraviolet-A LEDs. Our visibility extends down to about 400 nm, not 450 nm. They use additional broader blue phosphors instead of blue LEDs. But, violet and UV-A LEDs can never have the efficacy of blue LEDs because they have more energy in their photons. We generally wouldn't want to use these types of LEDs in grow light. Seoul Semiconductor Sunlike LEDs use violet LEDs.

• In most cases it's one photon per photochemical reaction also known as the second law of photochemistry. This applies to photosynthesis and to phosphors. You can have multiple down conversions with phosphors and not break the second law (i.e in a white LED, a photon can be absorbed and emitted multiple times always at lower energy levels), but this does not happen with photosynthesis. This means for photosynthesis that a blue photon does not drive photosynthesis better because blue photons have more energy than green and red photons, and the extra energy in the blue photons is wasted as heat in the photosynthesis process.

• 2700K has about 10% blue light, 4200K has about 20% blue light, 6500K has about 30% blue light. The greater the blue light content, the more compact the plant will be by reducing acid growth due to lower auxin levels. This is why people will say to use a higher color temperature in veging to suppress growth like stretching, and use lower color temperature in flowering to promote acid growth in flowering. Most higher end white LED grow lights are 3000K to 4000K.

• Higher color temperature white LEDs will have a higher electrical efficiency, all else being equal, because less blue light is being captured by the phosphors, and the blue light emitted by the LED does not take a phosphor conversion loss hit. The total phosphor conversion loss for a white LED can be 5-20% (page 3, above paper). Because there is a higher conversion loss with lower color temperature LEDs, they will run a bit hotter than higher color temperature LEDs. Lower color temperature (and higher CRI) LEDs will also have greater total Stokes shift heating (the energy difference between the blue photon emitted from the blue LED and the other down converted photon from the phosphor is wasted as heat).

• Some modern white LEDs may use five or more different phosphors or phosphors with multiple peaks, and I didn't really realize this until doing 1st and 2nd order derivative spectroscopic analysis on a dozen different types of Bridgelux white LEDs. The results can be seen here.. Early white LEDs were using a single yellow phosphor with blue LEDs and some still do.

• A "perfect" white light source would be right around 4.6 uMol/joule (it can vary a bit depending on the type of white). If you had a hypothetical 100% efficient array of color LEDs and a 100% LED driver to make white light, then you'll be around 4.6 uMol/joule, give or take a little. This is a theoretical limitation for white light no matter the white light source.

• Mixing warm white and cool white LEDs in a grow light makes no sense, and I consider it a marketing gimmick at best. An exception is if you want a variable color temperature grow light, then it makes sense to to mix warm white and cool white dimmable separately, or use dimmable warm white and blue LEDs to control the color temperature. I go with 3000K or 3500K for all around use for plant growing, but experiment with various 1750K to 6500K COBs, also (1750K is about what candle light is).

• I consider mixing red LEDs like 630 nm and 660 nm, or 450 nm and 470 nm, to also be a marketing gimmick, unless a clear demonstration as to their combined efficacy can be demonstrated in controlled grows (temp, humidity, CO2, and lighting levels consistent and does not significantly fluctuate to remove as many variables as possible). My first non-controlled experiments were in 2008 where I found no significant difference in 450-660, 450-630, 450-630-660 nm, and white light for a leafy lettuce cultivar. I soldered up a few thousand low power 5 mm LEDs to do these early experiments.

• There is nothing special about 6500K light for plants that may be used in veging and don't normally use it. Higher color temperature light usually have a higher luminous efficacy, and 6500K is about the highest color temperature that is tolerated for the consumer before appearing too blue. It's more often found in work spaces. 6500K is also the color temperature of the standard illuminate D65 used in photometry. 6500K has very little to do with professional grow lighting, and traditional (non-ceramic) metal halide is 4200K.

• There is nothing special about 2700K light for plants that may be used for flowering. It's about what incandescent bulbs roughly are and is close to the color temperature for the illuminate standard A used in photometry. You typically want to use this color temperature range or a bit higher for living spaces. Traditional HPS is 2100K.

• Although we tend to use higher color temperature white light for veging and a lower color temperature for flowering, I've gotten great veg growth with 2100K HPS for cannabis when LST (low stress training) techniques and higher lighting levels were used (500 umol/m2/sec). I've found greater growth at higher lighting levels but at lower color temperatures with various microgreens testing 2000K, 3000K, and 5000K light. If longer stems is what want (and what you get with lower lighting levels), but still want aggressive growth with larger leaves, play around with 2000K white LEDs at higher lighting levels for microgreens.

• CRI (color rendering index) tells us how well a light source does at accurately reproducing colors in an object relative to a natural or black body radiation source (e.g sun, incandescent bulb). It really falls flat, though, and a different standard has come out called TM-30. TM-30 doesn't actually replace CRI because they are standards from two different organizations, the CIE (International Commission on Illumination) for CRI, and ANSI/IES (American National Standards Institute/Illuminating Engineering Society) for TM-30.

• A major problem with CRI Ra is that it only measures eight pastel, non-saturated samples in their measurement. Not included are R9 (saturated red), R10 (saturated yellow), R11 (saturated green), R12 (saturated blue), R13 (white skin tone), R14 (leaf green), and sometimes R15 (south east Asian skin tone), which had to be added over time. Most CRI 80 lights have as R9 (red) value of 0, and CRI 90 lights are an R9 value of around 50. This is why you want to use high CRI lighting around food and for photography- CRI 80 is going to give you bland looking reds because of lower red chroma (saturation).

• CRI plays a larger role in lux to PPFD (umol/m2/sec) conversions than color temperature. Higher CRI lighting will have a greater amount of deeper reds, and deeper reds naturally have a lower luminous flux at the same radiant flux because luminous flux takes into account the sensitivity of our eyes by wavelength. In other words, the deeper reds have a lower luminous efficiency. You can see the differences in my spectroradiometer SPD charts here.

• You should consider using higher CRI lighting with plants that are also being used for display purposes (like orchids), particularly with plants that have red or purple colors. You should also be using high CRI lighting in your kitchen and dining room or wherever food is served, particularly for red colors like a medium rare steak. You can buy CRI +90 LED light bulbs and a quick google search shows a seller with CRI +95 (Cri 98 in their photometric data sheet).

• 100% efficient white LEDs would be fairly close to 260 lumens per watt for CRI 100, 280 lumens per watt for CRI 95, 300 lumens per watt for CRI 90, and about 320 lumens per watt for CRI 80. This can vary a bit by up to 10%.

• Red, green, and blue LEDs to make white light looks awful for general lighting because the CRI is around 40ish. The "rendering" part in CRI is about reflected light, and a RBG white light has relatively narrow spectral power distribution rather than a broader distribution, and the accurate colors of an object won't happen.

• What I said about objects having colors above is a lie. Objects don't have colors, light has colors and objects have specific absorption and reflection characteristics. Even that's a partial lie because color is a perception only, and we do not all perceive colors the same (e.g red-green color blind). "Color" is so much about our perception, the specific light, the specific subject, camera sensor characteristics, and different display characteristics which is why there are a multitude of different professional color standards.

• Fidelity Index (Rf) is used with TM-30 measurements and is sort of like CRI (0-100 scale with higher being better, but CRI can also have a negative number), but there's 99 color evaluation samples with a wide range of hue (base color), chroma (amount of saturation), and lightness. It is the average amount of "color smearing" in the 99 color samples, or the average of how far off one is from the color samples. That ultra high CRI bulb above has a TM-30-15 Rf of 94, and around 60 should be the minimum for indoor lighting (higher for living areas). A US Dept of Energy TM-30 tutorial can be found here.

• Gamut Index (Gf) with TM-30 ranges from 80-120 and is basically the amount of saturation with 100 being a neutral saturation. It is the color gamut area. Lower Gf white lights will make objects appear duller with higher Gf having colors more saturated.

• You can have a light with the same CCT, CRI, Rf, and still be different because the simpler numbers don't tell us the spectral power distribution. There's a good reason for high end studio photographers to keep gelling their lights as needed (professional videographers have their own standards on white coming out that takes into account the sensors in their cameras).

• Green LEDs are relatively electrically inefficient which is why they are not commonly used in grow lights. In physics/engineering this is known as the green gap (graph). We do, however, perceive green light much higher than red or blue light, so for display purposes this inefficiency matters less.

• Red photons have a lower energy with a higher theoretical PPE of about 5.51 uMol/joule (660 nm) compared to blue of 3.76 uMol/joule (450 nm). The higher efficacy is one reason why red LEDs are being added to white LEDs, what's held them back a bit is their electrical efficiency (red and blue LEDs use different semiconductor material).

• A red 660 nm LED that is 50% efficient would have a PPE of 2.76 umol/joule. A blue 450 nm LED that is 50% efficient would have a PPE of 1.88 umol/joule. A 450 nm blue LED can never be higher than 100% for 3.76 umol/joule, which is 68% efficient for a 660 nm red LED.

• Red LEDs have now broken the 4 umol/joule barrier in 2020 such as the Oslon Square Hyper Red by Osram (V9 bin 4.42 umol/joule at 350 mA for 80% efficient, and 4.04 umol/joule at 700 mA for 73% efficient). Currently, most red LEDs are significantly less.

• Osram is taking an interesting approach by having 4000K white horticulture LEDs that contain 15% less red than CRI 70 LEDs. This LED is then combined with their very efficient >4 umol/joule red LEDs.

• In some cases far red LEDs could be added depending on your design goals. For instance, far red could potentially help drive photosynthesis more efficiently as per the Emerson effect, but also tends to cause more acid growth (stretching in stems and petioles, larger leaves), which we may or may not want. Far red can also be used to control the photoperiod in some plants. High amounts of far red may encourage "foxtailing" in cannabis, and your specific cultivar would have to be tested.

• Adding UV LEDs are typically only used for light sensitive protein reactions effects, not as photosynthesis drivers per se. The pure UV-A grows I've done did result in slow grow and stunted plants. If I wanted to keep a tiny, important plant alive for a long duration I would be using pure UV-A. But, the effects of UV-A on a plant can be unpredictable and needs to be tested by cultivar. The theoretical maximum PPE of a 375 nm UV-A LED is 3.13 umol/joule, and the relative low photosynthesis rate is going to make them a no-go in LED lighting except for photomorphogenesis effects. Making red lettuce cultivars more red by increasing anthocyanin production, or trying to increase trichome and cannabinoid production in cannabis plants, may be reasons to use UV light.

• UV-A light is fairly safe (it can be dangerous when you stick your eye close to a light source that appears dim yet has a high radiant flux) and at the time of this writing, only UV-A LEDs are used in LED grow lights if UV light is used. The UV-B light sources I've seen in grow lights are still tube based because UV-B LEDs are still inefficient (5-10% range). UV-C should be considered dangerous, and in testing I have damaged a number of plants with higher amounts of UV-C.

• The main UV light sensitive protein known about currently is the UVR8 protein which is a 280-315 nm UV-B receptor, not a UV-A receptor.

• Apogee Instruments (Bruce Bugbee's company) have come out with a SQ-610 USB sensor for "ePAR" (enhanced photosynthetic active radiation) which counts light out to 750 nm far red, and also some UV-A at decreased sensitivity. With a long pass filter it may be possible to turn this into a red/far red light meter. They also have a new SQ-640 Quantum Light Pollution USB sensor that measures from 340-1040 nm. With the right filters, this sensor could have a lot of applications beyond light pollution measurements.

• "Hot swapping" LEDs is generally a bad practice with constant current or constant power supplies. This is where you change out an LED with the power supply still on. By lifting the load, a much higher voltage may be found in constant current power supplies. When the LED is applied, it's possible to get a very quick and short high current pulse causing damage which is accumulative. There are LED drivers where you can dial in both the maximum current and maximum voltage to make hot swapping safer. I've blown LEDs on lab power supplies because of of hot swapping and being careless.

• A silver mirror is fundamentally different than white although they can have the same reflectivity. The the main difference is that the mirror has a specular reflection where the phase information of the photons is preserved if the mirror surface is very smooth, and white has a diffuse reflection with photons being scattered. A mirror, being made out of a conductor, has a bunch of free electrons. These free electrons can oscillate when the photon strikes them, and this oscillation itself creates another photon i.e an opposing oscillating electric field is created that cancels out the original electromagnetic wave. Because these free electrons are not bound and have no discrete energy states, they have a broad range of energy levels they can oscillate at and a broad range of wavelengths of light that they'll reflect. This electric field interference also prevents photons from penetrating more than a few nanometers into the mirror's surface. I'm greatly simplifying all of this.

• If you have issues with cheap LED light bulbs burning out then stop buying such cheap light bulbs. Like most everything in life, you get what you pay for, and buy cheap buy twice.

Heat sink tips

• Only the energy input not radiated as light needs to be taken in to account for LED heat sink calculations. This is called thermal wattage. For example, a 100 watt COB that is 50% efficient would need a heat sink good for 50 watts of heat. A 100 watt COB that is 80% efficient would need a heat sink good for 20 watts of heat.

• A heat sink has a thermal rating or heat dissipation in units of °C/W, or the rise of the heat sink in degrees C per watt of heat on the heat sink. If I have a 100 watt COB that is 50% efficient (so 50 watts of heat) and want the heat sink to rise no more than 10 degrees C, I would need a heat sink with a heat dissipation of 0.2 °C/W. If I use a fan it may be 0.4 to 2 °C/W, depending on how much air the fan pushes and the particular heat sink geometry.

• I often size heat sinks that prevent the LEDs from going above 85-125 C for safety, and then use a quite fan to keep them at a temperature I want them to be. This provides an inherent fail-safe feature when experimenting.

• Rule of thumb I use: I try not to go above 125 degrees F (52 C), or where I can keep my finger on the heat sink for 4 seconds. My personal do not go over temperature is 145 degrees F (63 C), or where I can keep my finger on the heat sink for an honest one second. I've had second degree burns from electronics more than once.

• Temperature measuring tip: When working with a heat sink and a constant current power supply, you can monitor the voltage on the LEDs to see very tiny temperature variations that might not normally be measured with a temperature probe. With a constant voltage power supply, you can monitor the current to see very tiny temperature variations. This is because the I/V curves for LEDs are temperature dependent, and strings of LEDs make very high resolution temperature sensors. I use a 50,000 count data logging Fluke 287 for this purpose (I recommend a 6000 count multimeter for lower cost DIY. Every low cost meter I've ever tested reads within their listed specs when referenced to my Fluke 287, except for the occasional generic $5 meter that companies like Harbor Freight give away for free).

• 6063 aluminum alloy is the alloy with the highest thermal conductivity (around 210 W/m⋅K), and most common in heat sinks. The trade off is that 6063 is a softer alloy so common 6061 alloy (around 167 W/m⋅K) may be used instead in some cases. I've seen sellers advertise about using "aircraft grade aluminum" like 7075 alloy for metal core PCBs for LEDs, which is inferior for our uses (around 140 W/m⋅K). For comparison, copper is closer to 400 W/m⋅K, and steel is closer to 45 W/m⋅K.

• For a Vero 29 running at 120 watts I use a generic $30 CPU cooler with a fan and call it good. I've seen coolers half that price that should also work.

• I can run a Bridgelux gen 7 Vero 29 at 50 watts on the COB on a 40 mm heat sink with a 40 mm fan mounted about 1 cm above the heat sink to improve airflow. To be clear, I'm saying I "can" do this, and not I "should" do this! In these sort of experimental setups I'll use a bimetalic normally closed thermal cutout switch on the heat sink that trips at 70 C (158 F). I don't recommend beginners push DIY setups this hard.

• It is critically important that a thermal compound paste or thermal adhesive is used between the LED and the heat sink. You only want a thin layer, and I always twist the LED around a bit to get rid of air bubbles and get better overall thermal contact. If it's a heat sink/LED I'll never reuse then I'll use a thermal adhesive and just glue the LED down. Thermal pads can work at lower power levels but won't work as well as a compound/adhesive.

• When making mounting holes in a heat sink you can use a stainless steel screw as a tap. Drill a whole just smaller than the diameter of the screw, force the screw in to the much softer aluminum cutting the threads in the process (I use a ratcheting screwdriver for this), back the screw out, take a fine file and smooth out the burs completely, and you have a drilled and tapped mounting hole.

Power supply tips

• Get a Mean Well LED driver for DIY. The XLG are constant power and one work quite well with a Vero 18 or a Vero 29. A Vero 18 or 29 can be quickly interchanged at the same power level so you can rapidly measure the differences between the two if needed.

• I often use lab power supplies as LED drivers. If you only get one lab power supply make sure it's a linear power supply and not a noisy switching power supply. Lower cost linear power supplies typically have a fan that will turn on at certain current levels while more expensive and much heavier ones are entirely passive cooled.

• Power supplies have historically been the weak link in an LED grow light system and cheap capacitors are the main issue.

• The cheap boost converters you can buy on Amazon and eBay will work, but don't expect more than about 6 months use out of them. Again, it's the capacitors that tend to fail.

MacAdam ellipses and steps

The MacAdam ellipses, or SDCM (standard deviation of color matching), as used here are standard deviations of perceived color differences in LED binning including white LEDs. The higher the step or standard deviation, the lower the binning tolerances which lowers LED costs. Sylvania has a good, simple write up on this concept with a convenient graph below.

• MacAdam Ellipses: What are MacAdam Ellipses or color ovals?

• To make it simple and practical, only in a 1-step MacAdam ellipse for white LEDs are any variations in the white light unperceived to most all people with a trained person. In a 2-step MacAdam ellipse variations may just be perceivable to a trained eye, and in a 3-step MacAdam ellipse variations may be just perceivable to an untrained eye. Common quality white LED lighting for residential use tend to be two or three step, but can be 4-step and still be withing ANSI (American National Standards Institute) tolerances, which was causing issues in the past (a relative of mine is a commercial/industrial electrical contractor, and didn't understand why not all the thousand plus LED bulbs installed appeared the same. He didn't understand how white LED binning worked at the time).

• With LED grow lights we don't really care about minor variations in light, and the Samsung LM301H (horticulture) series of medium power LEDs use a 5-step MacAdam ellipse binning, while the LM301B (general illumination) uses a 3-step MacAdam ellipse binning. In other words, the LM301H has a lot more binning slop that is basically irrelevant to plant growth, but could be relevant for general illumination. The highest MacAdam step number used with LEDs is seven.

Don't worry if you can perceive slight color differences in the LEDs of LED grow lights! Your plants don't care.