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Topic: What kind of LEDs to grow plants? (Read 4912 times) previous topic - next topic


Hi all,

I am thinking about making a growing system for a few indoor plants (spices) that receive very little light.

What LEDs (colour and wattage) are best suited for this? Anyone with previous experience doing this?
The internet has a lot of conflicting information.



the debate arrises because nobody's certain which wavelengths plants respond to the mpst...


more wattage = better


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Google doesn't work for you?

Google returns a lot of conflicting information on that matter, saying everything and its opposite


It's not cheap, it all depends on how big you want your plants, how much money you want to spend..

if the plants are not going to grow 6ft tall, and are as you say herbs, you might not need much power, if they are going to grow tall and huge, then 100watt + you're looking at to do the job.



This is a cheap DIY endeavour, it's to grow parsley and chive. How many watts are enough for that you reckon?
In your link it is not clear whether it's a mix of red orange blue white LEDs or purple LEDs?


This is a cheap DIY endeavour, it's to grow parsley and chive. How many watts are enough for that you reckon?
In your link it is not clear whether it's a mix of red orange blue white LEDs or purple LEDs?

It's everything but green. Plants reflect green light -- that's why they look green.

The reason why they're using a mix of red/blue/orange is because they think they can get more useful lumens/watt than a white LED (which wastes some power creating green light in its mix). When you're burning hundreds of watts of power in a greenhouse you start looking at getting the most bang for your buck, but if you're just lighting a few sprigs of herbs then that approach is a bit overkill.

So you could trying mixing blue/red/orange with the satisfaction that you're saving a few pennies a year, and you might even save enough power to justify the higher market price of blue/red/orange LEDs ;). I'd suggest a cool white LED and be done with it.


It's everything but green.

confirmed by:

- http://www.lighting.philips.co.uk/pwc_li/main/shared/assets/downloads/pdf/horticulture/leaflets/cl-g-flowering_lamp-en.pdf -

- http://www.ehow.com/way_5315631_colors-light-grow-plants.html -
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)


The average power of sunlight ground level at the equator about 750 watts/SqM is seem to remember although I have read numbers from 1350 as the number that hits the outer atmosphere too.  Not absolutely sure here.

So that would be your maximum illumination.  Obvipously the watts need to be conberted to lumens an I have no idea how to do this for sunlight.

Now it depends which plants you wish to grow as some plants need more red (IR) whilst some grow better in sunlight containing more blue (towards UV).

LEDS are tailored to put out light at specific wavelengths and their output drops of very fast outside this.  An incandescent (filament) light bulb give out lots of IR (they're hot, right?) whilst fourescent tubes (sometimes inaccurately called neon tubes in some countries) put put more blue light.

I think that I would decide what I wishe to grow and then try to get a look at a pic of a professional grower environment of the same plant and see which lights they use.  Once you have this, find out the wavelength of these lights and then find LED(s) that conform to the same output frequencies.

I am sorry not to be more specific but there really are a lot of variables in here.

My daughter-in-law grows some plants in her kitchen under a brace of white LEDs and they do alright.


Oct 21, 2012, 02:56 am Last Edit: Oct 21, 2012, 04:08 am by Simpson_Jr Reason: 1
As far as I've understood 4 different wavelengths in the color spectrum are important in photosynthesis, 2 types of red (~620nM, ~660nM) and two types of blue (~440, ~470 nM).

Those are the most important 4, but Infrared and ultraviolet are usefull as well.  

The menu of colors required differs for each type of plant. Using just cheap normal red and blue leds (630nM and 470nM) will be enough for tomatoes for example, but other plants are lot more selective.

Leds emit a narrow bandwidth of light and you'll there for find growlights emitting up to 11-13 wavelengths on the market.

Since a lot of research is still going on, the effects of using a very large number of colors is also
questionable, It may... for example help to add Ultra-violet leds, but the lowest wavelength of an UV-led is about 390nM, while one of ~300 would be most effective. How much UV-leds contribute is therefor a question.

Led companies are also trying to cover every wavelength possible, but still have a hard time doing that. Using a lot of "non-standard" wavelengths is there for a lot more expensive. The 660 and 440 nM leds are already 2-3 times as expensive as common red and blue leds. Other wavelengths leds can cost much more.  In case your spices aren't that selective, it could be throwing away money.

What you would need is knowing the specific light requirements of the plants you want to grow. That can be quite hard since growing using Leds is still a relative new technique. There is some... data available, mostly agricultural, but a lot is still uncharted.

I don't know which spices you want to grow, personally I grow weed. What I know from fellow growers is that growing using led lights is great to decrease the costs of electricity, but that it can be quite hard to grow using leds only. Besides leds a lot of them use other light sources as well. CFLs for example cost close to nothing and emit a much broader bandwidth. Using a few cfls as well will give the plants at least some of the missing wavelengths resulting in better crops.

What I know of led-growlights is that they often use a ratio of 5-6 watts red to every watt blue.

It may be an idea to divide the led-part in 40% 620nM, 40% 660nm, 10% 440nm and 10% 470nm. Using extra non led-light as well a ratio of 20-25% non-led light and 75-80% led-light might be an idea. Unfortunately it's hard to give good advice on led grow since so much still is unknown.

The suggestions I make are by the way  more complicated since I should mention all light emitted in lumen instead of watts. Led development is going quite fast and there is a huge variety in output per watt, depending on which fabrication method is used. To get a good balance in light one should keep that in mind as well. Using old types red, new types blue or vice versa will make a lot of difference.

Last grow remark, besides needing different wavelengths of light, the needs of plants are different during the whole journey from seedling to crop. While growing a little more blue is better, while flowering more red.

Personally I grow in a 2x3 ft (50x75cm) closet, have used 200 watts CFL so far and am planning to do the opposite of a lot of fellow growers by keeping the CFLs and adding 40 watts of common 630nM red leds.

If you ask me using leds for growing probably will be a matter of experimenting a lot for the next decades.

When building your own "sun", keep in mind that plant-DNA has developed in millions and millions years.
Plants there for  "expect" seasons to be as they should and react on the difference in hours of daylight they get. One can "fool" plants to a certain degree by starting to grow in "summer" and after growing going from "summer" to "autumn" quickly, but if they "think" it's a certain season since you've set the clock a soft-/hardware failure resulting in 24/7 daylight or non at all will have a lot of effect in the development of the plants.

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