What type of LEDs are used for grow LED lights?


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RikJ11 year ago

how can you calculate what the best mix of led diodes is than? because the spectra is found every where but no info about the mix of red bleu green uv and infra red

Short answer: Plants evolved under sunlight. The best thing to do is to duplicate sunlight, which means providing full spectrum lighting.

Less short answer: Chlorophylls turn light into energy in plants. Chlorophylls are greenish pigments, and each type is sensitive to particular wavelengths of light. Land plants use chlorophyll a and b. Both types have two small spikes--small frequency ranges that they're most sensitive to. Type a absorbs UV (below 400 nanometers,) up to around 470nm, and also at the red end in the ~560nm to ~700nm range. Type b absorbs more weakly in the UV--let's say ~420-490nm, and orange/red light at around 600-680nm. It's easiest just to lump those sets of ranges together and say 400-500nm, and 600-700nm. (These aren't hard numbers; just me glancing at a graph and estimating.)

Most commercial LED grow lights put out 5-8 times as much red light than blue. Plants don't use 8x as much red light as blue, though. It may be partly because red LEDs have been around longer, and are cheaper and more available than blue. Violet, "hyperviolet" (near UV,) and ultraviolet (outside the visible spectrum,) LEDs are a relatively new thing. Bright blue LEDs have only been available since the early 90s. A photosynthetic response graph of chlorophll a & b shows that light from below 400nm to over 700nm is absorbed. We probably don't know everything about how plants use light, but you can provide a only couple of frequency ranges and grow nice, healthy plants. That response graph has lumps centered at ~440nm and ~640nm, but those are peaks, not the whole mountain.

Fancy commercial LED grow lights might have 10 emitter types at different frequencies, while the cheapest have 2 or 3. Some even have customized emitters with specially formulated phosphorus to create special light magic. Apparently, they're working very hard to cover the visible spectrum, while imbuing some colors with mystical importance. Seems to me that it's easier to just use full spectrum lights to begin with, possibly supplementing with some deep blue and far red. The grow setups I've seen in recent years have used plain, old CFL bulbs; 2700K and 5000k. Maybe not ideal, but it does tell me that unenhanced white light can grow big, productive plants.

In building LED grow lights there seem to be two general approaches: 1) Use a small number of high-power (5 or 10 watt) white/broad spectrum Chip-On-Board (COB) LEDs; mostly warm white (2700K,) and some daylight (5000 Kelvin,) or 2) Use a lot of individual LED emitters at 5, 6, 8... maybe even 10 specific frequencies. My thumbnail is that you'd want to cover two ranges, say, 400-500nm, and also around 600-700nm, but that isn't a scientific answer, it's just an easy answer. Yes, you could focus on 650nm, but that's right in the valley, between the absorption peaks of types a and b chlorophyll; you want both sides of that.

I've found all sorts of good and bad data & dis/information, but this theory+practical write-up a good one: http://goo.gl/F8IVc6. This guy uses four 2700K (warm/red,) COB LEDs, and one 5000K for a 2'x2' space. His build and gear are kind of high-end/overkill, I think, and components he used are less expensive now. He supplements with two CFL bulbs, which I would also do. Since that was written, cheaper, more efficient LED COB modules have hit the market. There are good inexpensive drivers, and easier approaches to cooling. (like aluminum square stock w/ a fan at each end.) He doesn't bother salvaging obvious stuff like old computer power supplies, which are good, cheap, and easy to find. I suspect now you could make something equivalent for under $100. I'd use old PC power supplies, cheaper drivers, aluminum square stock w/ airflow as heat sinks... I truly don't think that many exotic LED colors are necessary.

In nature, the plant goes through two main phases: vegetative and flowering. Vegetation starts at the beginning of summer, as days are getting longer and the sun gets high overhead. Toward the end of summer, days get shorter, and the light gets redder as the sun sinks toward the horizon. (Sunlight coming at more oblique angle passes through more atmosphere, and is more yellow/red than when straight overhead.) Shorter days induce the plants to enter their flowering phase.

When growing under lights, some people provide more blue/daylight light in the veg phase, and more red in the flowering stage. The duration of the light is key, but the color change may have an effect. I don't know. I do know that you can induce flowering by going from 18-20 hours of light per day to 12 hours without adding red light. I like to try and mimic nature, but I can't say whether the plants appreciate it or not. It makes sense that the flowers might be attuned to the redder light of late summer.


I know that your post has been here for some time. There are uv leds that can be purchased but I don't know the wavelength they emit. Thought you would like to know.

There's the LUXEON Z UV package. Those go down into the ultraviolet, and up above 400nm into what's being called "hyperviolet." Those span the 380-420nm wavelengths. They cost ~$15-20/ea. stevesleds.com has SemiLeds Hyperviolet stars that emit at 415-425nm. Those are currently $3.90/ea.

If you're doing something like curing dental epoxy you might need a 365nm light source, but I'm not sure whether that would help with photosynthesis or not. It might! Great way to burn your retinas! (Seriously. Wear UV goggles when working with intense UV/HV sources. Retinas don't grow back.)

For LED grows you want to know the ratio between spectrums first of all. That prereq depends on what sort of crop you are growing.

And the better your aim, the better result.

The majority of the emitters in a LED-array should be in the 660nm spectrum for general use.general. The next largest would be (depending on who you ask) 740nm or 450nm. Personally I'd focus on 740nm after 660nm for a good result and make the third largest the 450nm. The border spectrums to green from both directions are active, but in general, there is little point in adding emitters for these. A spectrum between the 450nm and 395nm could however be usable, but from what I've seen, those are fairly hard to come by.

Keep in mind LEDs usually vary in their spectrum +-20nm. So with a middle spectrum you should cover the overlapping spectrums as well as is the case with 740nm, the spectrum you really aim for is 730nm.

Be advised 740nm is visible to humans even if it's faint which IR isn't, but it is to plants. Some use IR as well as supplementary spectrum.

The general multiband tailormade horticulture LED spectrums are:

~400nm (UV) >1%

~420 (Purple)

~450nm (Blue)

~480nm (Turquoise)

~590nm (Yellow)

~630nm (Red)

~660nm (Deep Red)

~740nm (Far red)

~850-950nm (IR) >1%

I cannot stress enough how important the ratio between the spectrums are. You are better off buying 100W warmwhite+coldwhite emitters, they provide enough light to give a good result. If needed you can always add supplementary spectrums in the UV and Deep/Far Red and IR spectrum.

Mogger8 years ago
noahw8 years ago
monchito7 (author)  noahw8 years ago
110100101108 years ago
the way i understand it : each plant needs various ranges of light - each for another need. the light source should match as much as possible the needs of the plant - supply enough light in each range here are some images that show this (the light sources are taken from lamptech.co.uk) some plants need dawn-like light to grow and day-like light to flower
monchito7 (author)  110100101108 years ago
rachel8 years ago
monchito7 (author)  rachel8 years ago
monchito7 (author) 8 years ago
Thanks for the replies everyone much appreciated.
jeff-o8 years ago
monchito7 (author)  jeff-o8 years ago
Thank you very much, makes sense:)