LED Grow lights

[buddy roo]

Hi All, i have searched the net a few times till my eyes melted looking for just the right grow light for starting seeds indoors and growing small seedlings like,jabo's grumichama exc.  i read that some light is good for dark green leaf some for stocky bushy growth some for strong root devel.   i have read that you need a % of reeds to a % of blues to a % of greens and whites , most of the lights i see advertised are designed for the pot growers with a lot of extra reds for growing large blooms and flowers, not what i need  due to my lack of  experience on the internet once i change pages i can never find that last article  twice, the lights i have been looking at are around 40 to 45 watts and around 10 to 12 inches sq. in the price range of $25. or so ....SO my question is dose anyone have experience with these and know what is the best one for my needs??          Regards     Patrick

[KarenRei]

Okay, take a step back    A couple truths about LED grow lights.

1) Sellers lie.

2) Some things about how plants grow in different conditions are well understood.  Others are generally believed, but there's some controversy.  Some are very much up in the air.  Some are true but only apply in very specific conditions. Etc.  It's not realistic that you'd get a solid grasp on all of the nuance in a short period of time.

As for red and blue:

Red is the most wall-plug-efficient frequency for photosynthesis. Blue light, on a per-photon basis, is slightly more efficient at photosynthesis in practice due to its better penetration, and blue LEDs are more efficient than red, but blue photons contain a lot more energy than red ones, and this overcomes the efficiency differences.  So if you want to max out photosynthesis, it's pure red that's the choice.

But of course, colours have an effect on plant hormones.  Exactly what effects, and whether they're a good thing or not, depends on the species.  Blue tends to encourage more compact growth and root development, while red encourages petiole elongation (growing bigger and lankier) and, in some species, flowering, with less focus on the roots.  For people growing crops of lettuce, for example, some studies suggest that pure red yields the best growth per unit watt (although not every study is in agreement).  But I wouldn't recommend that for long-term plants like trees. 

The simple fact is, however, this is no hard fast rule about how much red. vs. blue will be best for your situation.

As for other colours: there's a myth that yellow/green/amber don't do anything for plants.  In reality, photosynthesis works fine with them (as should be obvious from the fact that the traditional way to grow plants under lights in greenhouse has been HPS lights, which are yellow with a strong green spectral component).  Indeed, under heavy red-blue lighting conditions, adding green (on a per-unit-energy basis) can actually cause *more* growth than adding more red or blue; the surface becomes saturated, while the green penetrates better, particularly with inter-reflections.  But again that's very much a situation-dependent scenario. 

Some various hormonal effects to yellow/green/amber light can occur.  In most plants they're small, but you never know.  I personally think it's worth it to have a bit of your light in this range - just not too much.  You can provide that light with white LEDs (most common) or yellw/green/amber LEDs (less common).  Neither are very efficient.  Having some white / mid-wavelength light also makes it easier to see details on your plants; leaves look black or purple under narrowband red/blue light.

When shopping for fixures: the larger the fixture's surface area and weight relative to its power output, generally the better.  Larger fixtures run cooler (more heat sink area), which increases their lifespan. It's also a sign that the manufacturer is willing to spend more to make a higher quality product.  If you can get your hands on it, look for a wall-plug efficiency (WPE) figure or, more commonly, a umol/s/W figure.  Just beware of rule #1: sellers like.  Particularly no-name Chinese brands on Ebay and Amazon.      The power or light output may not be what they claim it is.    A high quality fixture may be as much as 45% WPE and ~2,7 umol/s/W for a mostly red fixture and ~40% WPE and ~2,3 umol/s/W for one with more blue and a bit of white or UV or whatnot broadening the spectrum.

Or.... you can just not fret about it and just focus on watts.  There are differences in LED fixture efficencies for a given spectrum, but they're not some sort of vast differences.  If you want to be relatively safe... get whatever fixture you want... plug it into a kill-a-watt or other wattmeter and measure how much power it's drawing.... and if it matches the ad, call that good enough.  If it draws less than they claim, demand a refund from the seller, as they overrated it.   Another thing you can do is get a couple of fixtures from different sellers, and (so long as the spectrums are similar), if some look clearly dimmer for a given amount of power output, they're probably cheating / cutting corners somewhere.

Lastly: 40-45 watts is almost nothing.  Hope you're planning on covering only a very small amount of surface area with that light.

[buddy roo]

Hi Karen,, thinks for the input i am only looking to cover less than 1 sq. foot but later go to 4 sq. ft but the main thing is the quality of lighting.   thanks     Patrick

[KarenRei]

Hi Karen,, thinks for the input i am only looking to cover less than 1 sq. foot but later go to 4 sq. ft but the main thing is the quality of lighting.   thanks     Patrick

Okay, that's actually good lighting for 1 square foot; I think you'll have some happy plants 

If this is indoors, also don't forget about your plants' humidity needs, whatever they may be!  And also if they're in an enclosed space, don't let them overheat - even tropicals can get "heatstroke"! 

[buddy roo]

I think what i am really looking for is the ratio of red lights to blue, green and white

[gozp]

Since the OP is asking about growlights.

Mind if i ask u Karen of what are your thoughts on 1500w COB LeD lights full spectruM?

[KarenRei]

COBs are good, although they're not the be-all end-all of LEDs.    But it is a good tech; all else being equal, I'd choose COBs for their better cooling potential and fewer opportunities for bad connections - particularlly from a source of questionable quality.  That said, I wouldn't put a huge premium on them, like some sellers want.  You can compare efficiencies on COBs by looking at the tech specs on bulk LED sales, and COBs don't come out any higher than non-COBs.  I'd also choose a larger non-COB fixture over a smaller COB fixture any day.

Full spectrum means different things to different people.  Sometimes it's used to mean broader red/blue peaks with a small amount of green/yellow/amber and sometimes UV or NIR. And that's great.  But sometimes it's used to mean white or mimicking the solar spectrum, and that means that that you spend a lot more money in power for a given amount of photosynthesis, for a questionable amount of benefit.  A high quality light matching the solar spectrum will usually get only ~1,5 umol/s/W (under 30% WPE).

[SoCal2warm]

I've seen an experiment that showed plants grow better under regular white LED light than they do under red + blue grow lights. This is apparently because other wavelengths of light are important too. There are different photosynthetic pigments that absorb other wavelengths, so I think if you're just using red + blue, some of the photosynetic receptors might be getting overstaturated (i.e. there's only so much energy the plant can absorb from any specific wavelength). However, I've also seen another study that showed higher growth efficiency the more red there was. I'm pretty sure red is the most efficient wavelength at driving photosynthesis. So ideally then, the optimal mix would involve both red and white light.

Another reason other wavelengths of light are important (i.e. green or white) is because blue light actually has limited penetration through the tissues of the leaf, since it get absorbed so strongly. This limits the utilization of this wavelength in the leaf. Wavelengths less strongly absorbed (such as green) will have much better penetration and be able to drive more photosynthesis, paradoxically. If you're only using blue wavelengths, you'll just be over saturating the chlorophyll on the surface layer of the leaf and it won't do as much good. Deep red wavelengths of light have medium penetration, somewhere between blue and green.

In addition, there are two different peaks of chlorophyll absorption, since there are two types of chlorophyll, 660nm and 620nm. Several of the photosynetic accessory pigments dump their energy to the 620nm type. So by this reasoning perhaps 620nm (red-orange) could just be used instead of white light, but I don't really know.

One last thing- blue LED emitters have become very efficient now and so the efficiency of using white LED light (white LEDs are driven by blue emitters) by itself is not going to be more than 20% less energy efficient than using any other combination that also uses red LEDs. There's simply been a lot more research going into trying to make blue LED emitters more efficient because they're used in white LEDs, which have become ubiquitous for general lighting purposes. This despite the fact that the theoretical quantum efficiency is lower, having to generate a wavelength that requires 25% more energy, with a small degree of additional loss in the phosphor conversion to the other wavelengths (white light).

I might also point out that the theoretical optimal mix probably depends on the light intensity level. If you're not using enough light then I would say red would be the most important, followed by a small amount of necessary blue (to signal the plant to grow). At very high light levels oversaturating the plant then white would be the most important, I think.

As for me, what I'm doing is using 5000K bulbs, the highest efficiency ones I can find that are not too expensive, and supplementing that with some lower wattage "energy saving" halogen bulbs, although in one case I'm using a 660nm deep red flood lamp instead. The idea is that the halogen (a form of incandescent) has plenty of deep red wavelengths, and anyway the small amount of additional heat they're giving off isn't hurting. (Hardly makes sense not to be using incandescent light if you're also running an electric heater at the same time) All in all I'd say the overall wattage is evenly split between the halogen and LED. If I was running a large scale commercial operation I would probably be choosing a mix of 660nm deep red, white LED, and perhaps a small amount of added blue. Perhaps a little 620nm if it wasn't too costly to add it in.

[SoCal2warm]

If you're spending less than $30 for a cheap red + blue LED grow light manufactured in China, it very likely (read: almost certainly) won't actually be the wattage claimed. (If it claims to be 45W it will very likely actually be 32W, as an example)

Furthermore the overall efficiency of these lower cost grow lights are likely to not be as high as a typical white LED bulb you can find at the store for very cheap. So, I would ask, are you really gaining much advantage by using a special red + blue grow light? At the very least you might think about some combination of the two together.

[KarenRei]

I've seen an experiment that showed plants grow better under regular white LED light than they do under red + blue grow lights.

For a given number of photons, in most situations (not all), yes.  The problem is that you don't get nearly as many photons per watt with white as you do with red-blue.

Photosynthesis is carried out on a per-photon-absorbed basis.  And regardless of frequency, the vast majority of light that strikes a leaf ends up absorbed.  Yes, there are differences in utility between different frequencies (although there are no hard-fast rules - start reading scholar.google.com and you can find a study that contradicts almost any other study    ).  But they're not huge and don't make up for the fact that 1) Red LEDs are moderately efficient and red photons are cheap to make, 2) Blue LEDs are highly efficient (although blue photons are expensive to make), and 3) white, yellow, green, and amber LEDs are very inefficient.

Look at the LED fixtures that commercial greenhouses use.  Look at the fixtures that NASA uses.  They're red-blue for a reason.  Red is simply the cheapest way to drive photosynthesis, in almost all realistic situations.  Everything else is just about hormonal triggers - blue addressing the most significant of them (excessive petiole elongation) in a rather efficient manner.

One last thing- blue LED emitters have become very efficient now and so the efficiency of using white LED light (white LEDs are driven by blue emitters) by itself is not going to be more than 20% less energy efficient than

This is simply not true.  Check out umol/s/W (umol/J) figures for commercially available fixtures from the same manufacturer.  White fixtures generally yield about 2/3rds as much flux as blue/red fixtures, at best.  For example, Senmatic's "sunlight" fixtures  are 1,5umol/s/W, while their red-blue lights are 2,3.

[KarenRei]

If you're spending less than $30 for a cheap red + blue LED grow light manufactured in China, it very likely (read: almost certainly) won't actually be the wattage claimed. (If it claims to be 45W it will very likely actually be 32W, as an example)

Agreed.

Furthermore the overall efficiency of these lower cost grow lights are likely to not be as high as a typical white LED bulb you can find at the store for very cheap.

Not even remotely close to agreement.  Making things even worse is that white LED bulbs designed for illumination try to maximize frequencies close to green/yellow (the least efficient frequencies) while minimizing blue/red (the most efficient frequencies) because human eyes are most sensitive to them.  You'd be lucky to get 1,5 umol/J.

Start browsing LEDs.  Examples here:

https://www.digikey.sg/products/en/optoelectronics/led-lighting-color/125?FV=940003%2C1500000a%2C15000066%2C1500000e%2C1500002d%2C1500002f%2C15000006%2C15000049%2C1500005a%2Cffe0007d&mnonly=0&ColumnSort=-1344&page=1&stock=0&pbfree=0&rohs=0&cad=0&datasheet=0&nstock=0&photo=0&nonrohs=0&newproducts=0&quantity=&ptm=0&fid=0&pageSize=25

Ignore the first 3-4, as they're longer wavelengths than the rest so they inherently get more lumens per watt (a horrible measure for LEDs, but I digress).  Compare the rest that are clustered around the same frequencies, from different manufacturers.  Notice how little difference there is between their output per watt.  And part of that can be accounted for by minor frequency differences.

Go ahead and do the same for red or any other colour.  For a given frequency (note: the frequency has to be the same for lumen per watt comparisons!), there's rather little difference between efficiencies.  Yes, there are some differences, but they're not huge.

Cheapo manufacturers buy their LEDs in bulk from the same sort of places as everyone else.  They don't make their LEDs, they buy them from big manufacturers; an LED is not something you can whip in up your garage.

[SoCal2warm]

The problem is that you don't get nearly as many photons per watt with white as you do with red-blue.

That's true.
Which is why theoretically red-blue is the most efficient (but again that's very theoretical, and may depend on a number of other factors).

Photosynthesis is carried out on a per-photon-absorbed basis.

Not sure I agree on you there. Light absorbed by the leaf does not automatically mean it was necessarily converted to energy.
I think while green light has a much lower absorption rate (and thus lower conversion), of the light that is absorbed it may have a higher conversion efficiency.

(This isn't an argument for using green LEDs, since current technology green LEDs have the lowest amount of efficiency, about half that of red or blue)

But they're not huge

I agree.

Red LEDs are moderately efficient and red photons are cheap to make
 Red is simply the cheapest way to drive photosynthesis

Yes, theoretically if you just wanted to dump energy into the plant red LED would be the best way to go about it.
(Although plants don't seem to grow very well unless they have some blue light)

white, yellow, green, and amber LEDs are very inefficient.

Actually white LEDs are not that inefficient (although they're certainly less efficient than blue).
I'm just saying it wouldn't be a terrible terrible loss if you tried to use white LEDs to grow plants, especially at the higher color temperatures.

Look at the LED fixtures that commercial greenhouses use.  Look at the fixtures that NASA uses.

I wonder if NASA has ever run side-by-side tests comparing plants grown under red-blue light and plants grown under different combinations of red-blue and white light.

If NASA was really aiming for optimal energy reduction then one would assume red-blue would be the way to go, but it may well be sacrificing growth rate.
That is, if you're going to under-power the plants, then you probably could get away with higher efficiency using less light.
But these are not necessarily the same growing conditions everyone is going to use.

I've never come across any study comparing red+blue lighting to red+white, or red+blue+white.

This is simply not true.  Check out umol/s/W figures for commercially available fixtures from the same manufacturer.

It's more likely true for the cheap LED grow lights.


I'm just saying that plants are more likely to grow better under red+blue+white than they are under just red+blue.

I did see one study that compared different combinations of red-green-blue wavelengths, but the study is not directly applicable here since they were using a green emitter, which has substantially lower efficiency than the green wavelengths coming from a white LED, and for other reasons.

I'm saying that if you had to compare between using a cheap red+blue grow light and just using a regular white LED bulb, you might not be so bad off deciding to use the bulb.

[KarenRei]

The problem is that you don't get nearly as many photons per watt with white as you do with red-blue.

That's true.
Which is why theoretically red-blue is the most efficient (but again that's very theoretical, and may depend on a number of other factors).

It's not "theoretical", it's basic physics.  The amount of photons you get is always  the efficiency times the amount of energy per photon times the input power. 

Photosynthesis is carried out on a per-photon-absorbed basis.

I think while green light has a much lower absorption rate (and thus lower conversion), of the light that is absorbed it may have a higher conversion efficiency.

That is a physical impossibility.

https://en.wikipedia.org/wiki/Light-dependent_reactions

You move one chlorophyll molecule to a higher energy state per photon.  It's impossible to move more than one to a higher energy state with a single photon.  Now, it's possible to have different frequencies be more or less likely to end up absorbed by chlorophyll (after taking into account reflections and an integrated sky sphere approach) - and indeed, there are differences.  But they're not huge, and they're not even consistent between plants and illumination conditions.

Look at the LED fixtures that commercial greenhouses use.  Look at the fixtures that NASA uses.

I wonder if NASA has ever run side-by-side tests comparing plants grown under red-blue light and plants grown under different combinations of red-blue and white light.

Do you think NASA's horticultural department is run by idiots?  That they just send things up to the space station and build large-scale system prototypes without ever bothering to test the best way to do something?


(Above: growing lettuce on the ISS)


(Above: NASA prototype lunar greenhouse)

[SoCal2warm]

It's not "theoretical", it's basic physics.  The amount of photons you get is always  the efficiency times the amount of energy per photon times the input power.

It's not as simple as that.
If we were talking about generating photons with 100% efficiency and having them be absorbed by a single molecule of chlorophyll, then yes you would be completely right.


Here's a real world test that shows the difference between growing a tomato plant under a 38 Watt red+blue lamp versus a 50 Watt white LED lamp:

https://www.youtube.com/watch?v=HawgP5SXPko

Obviously not exactly a fair comparison because of the difference in wattage but the plant grown under white light obviously does much better.

Here's another experiment that shows plants grow better under white LED light than they do under either red or blue light alone, keeping wattage equal:

https://www.youtube.com/watch?v=mwwLSgK-924

[KarenRei]

Here's a real world test that shows the difference between growing a tomato plant under a 38 Watt red+blue lamp versus a 50 Watt white LED lamp:

https://www.youtube.com/watch?v=HawgP5SXPko

I'm sorry, but random Youtubers' poorly controlled, non-peer-reviewed home experiments do not count as "science" (just ignoring that one of the fixtures is 31% more powerful in nameplate than the other, there's no attempt at measuring the light flux and no measurement of real-world power consumption, which is often lied about concerning cheapo LED fixtures).

This is peer-reviewed science. For example, from one of the first ones (happens to be about spirulina, but whatever):



(Sun over the course of a day in the tropics = ~1000 umol/m²-s average, ~3000 umol/m²-s peak. Caution that the red and yellow symbols are swapped in (c). Frequencies: red 620–645 nm, yellow 587–595 nm, green 515–540 nm, and blue 460–475 nm.  Looks like they *overgrew* the sample at 3000umol/m², as the population starts to decline at the end)

The above biomass accumulation rates are with directly measured photon intensities.  For the same number of photons (while in reality you get a lot fewer PAR photons with white LEDs than with red).  I'll repeat: there's a reason that professional growers use lights dominated by red, not white.  You drive with red, and use blue as needed to prevent petiole elongation.

If all else was equal, white would be "second best" to red at driving photosynthesis.  But all is not equal. A) white LEDs are lossier, B) part of the energy lies outside of the PAR spectrum, and C) photons in the "white" spectrum contain more energy on average. 

[MattEdmunds]

Spammer