LED grow lights: will they grow cannabis?

and more importantly, will they flower them?

LED grow lights have exploded in the last few years with more advanced versions seeming to appear monthly. But among marijuana growers there is heated debate on the subject, with traditionalists yet to be converted to the new technology. For newbies the problem is often wading through the techno talk to get to the truth. Lets get back to basics.


LED lights: a brief history

As early as the beginning of the 20th century a British scientist, experimented with a solid state light emitting diode (LED), but it wasn’t until the late fifties before his research was taken seriously. In 1962 the first practical visible spectrum LED was developed by American Holynak, “the father of the light-emitting diode”. Initially used in a variety of settings, from TVs to watches, it has only been in the past 10 years that problems with reliability, stability, strength and spectrum have been resolved. Where once LEDs were used mainly for red indicators in electronics, they have now moved into all wavelengths, including visible, ultraviolet and infrared.
Research by scientists such as those at NASA and corporate development aimed at horticultural businesses worldwide have refined the specifications to the point where LED lighting is not only a viable form of alternative grow lights: it is possibly the future of grow lighting technology.


So how do LED grow light systems work?

An LED grow lamp looks very different from an HID grow light. Whereas the latter looks like an oversized industrial light bulb capable of kicking out a lot of brightness and power (which it does), the LED systems are self-contained boxes full of tiny bulbs. Each grow bulb is small in area (less than 1mm2) and uses integrated optical components to shape its radiation pattern and reflection.

To understand why LEDs are being promoted as a superior option for growing cannabis than HID grow lights, its necessary to understand the principals of wavelengths for chlorophyll absorption.




In its simplest form, the plant uses blue light for growing, and red light for flowering.

The process whereby plants grow is photosynthesis, whereby CO2 is converted into organic material using energy derived from sunlight. This energy is absorbed through special proteins containing chlorophyll, BUT chlorophyll only absorbs light from particular parts of the spectrum. For example, it uses hardly any “green” light but instead reflects it, hence the reason plants are green.
And its here that the first LEDs to be experimented with for growing cannabis got a bad name. They just used a single band of blue and a single band of red. This is fine for simple crops but failed when launched onto the market for more complex plants – such as cannabis

Today’s more sophisticated LED grow lighting systems produce light at the correct wavelengths of growing and flowering cannabis by combining four separate LEDs into clusters, each bulb emitting light at one of the four chlorophyll absorption peaks.

For cannabis growing, you want to see lights aimed at 439nm, 469nm, 642nm and 667nm.

Because each individual light is specific to a certain point in the spectrum, a system of lights covering say 1m2 will contain percentages of light colours to provide optimum use by the plant at all stages of its growth. The ratio of between 4 – 8:1 red:blue is now often augmented by additional orange components. It’s claimed that up to 90% of LED light is utilised by the plant.
In comparison, while HID lights do tend towards one end of the spectrum – i.e., metal halide for blue light, high pressure sodium for red, the light you see is more like an intense standard light bulb: they emit light through all the spectrum. Between 15 and 30% of light produced by an HID is within the wavelengths suitable for cannabis growth. This is why they need to be so powerful, so that that 15 – 30% is strong enough for good growth.


The Advantages of LEDs for growing cannabis

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  • LED grow lights emit light at optimum wavelengths

    A good LED grow light provides almost only the spectra of light that the plant needs, with hardly any wastage. In theory this means bigger, better plants.

  • Heat

    LED grow lights produce virtually no heat. This means that less investment, energy & thought has to go into dealing with heat extraction. Assuming that your grow room is located within your home environment, you probably keep the ambient temperature at around the ideal growing temps.

  • Low running costs


    • Electricity bills are said to be between 40% and 75% less than an equivalent HID or CFL system (including reduced amounts used for smaller extraction equipment, no air con etc)
    • LED grow lights have no filament system to burn out, and have an expected lifespan of 50,000 hours
    • There are no ballasts, reflectors and so on to be replaced.
    • Because there is no heat, it is not necessary to spend a lot of time, energy and expense dealing with it: only a small extractor system etc
  • Security

    Of course, we all believe that readers of this article possess medical marijuana growing certificates. But just in case you don’t, this aspect of growing cannabis using LED grow  lights is a compelling one. As more and more marijuana grows are discovered due to either suspicious increases in electricity usage or as a result of heat signatures, any system that creates neither of these has to have a large stealth bonus.  LED growing also produces virtually no noise – there’s no give-away electrical “hum”

 led grow cannabis


Size of grow room

OK, so we’ve all measured up in a new location and had to factor in space for distance from plant at maximum size, size of reflectors, sturdy mountings for ballasts, fans, extractor fans with tubing and so on. With LED growing none of these elements need to be considered. LED grow  lights can be much closer to the plants, and without all that excess equipment needed, it really is possible to grow in a small space, discreetly. See here for more information on constructing your own LED grow box.

 What must be remembered is that the science of growing marijuana indoors is not to replicate the natural environment, but to optimise it to the nth degree. Hydroponics produce great results because they enable the cannabis grower to define exactly the correct amounts of certain nutrients available directly to the plant through water, which is itself kept within a certain pH range. Similarly he/she controls the ambient temperature, introduces carbon dioxide, sets the length of time light is available. With LED lighting, it is possible to exercise even more control over the quality as well as the amount of light available for the plant

Do LED grow lights work as well as HPS for cannabis grows?

See here to read about our comparison grows



We’ve been growing weed indoors for 16 years now, moderated on forums, and as this blog shows, been quite obsessive in our quest for quality. Two years ago we started using Fero LEDs .. why? Well for all of the above reasons .. and because they work. We’d recommend using LED grow lights to any small grower who wants to be discrete. 

5 thoughts on “LED grow lights & cannabis grows

  1. Illyje Xichelliatan Ollenia says:

    What should the led bulb specs be? I have 24led, ac 110/220v, power 1.4w . Is this good or do I need different bulbs?

    • campo cultivator says:

      hey there illyje
      well mate to be honest you would be better off from my experience using a 3 watt diode I find the 1 watt diode lacks penetration
      try these guys http://www.feroled.net they have full spectrum information and a lot more knowledgeable than myself, as to be honest all that technical mumbo jumbo makes my head hurt.
      yeah sure i grow with them and have a good working knowledge in the application but little beyond that :)
      Happy Tokin’

    • weed widow says:

      Really you need to find out the nm of these colours and match as much as possible the twin “peaks” on a PAR diagram. Pesonally I don’t think the UV helps at all, the plant suffers more than it gains from UV, but I havent run any tests so prove this. Your white will contain minimal amounts of all spectrum and cover the tiny amounts of eg green that the plant does use (and hence I wouldn’t use green, it really is a waste of power as hardly any at all will be used by the plant). Your red to blue ratio (assuming the nms are similar to the peaks mentioned above) should be at a roughly 2:1 ratio. Hope that helps!

  2. max garascia says:

    uv light promotes tricrome production . the best cannabis comes from high altitude equatorial climates (hindu kush).I repilcate high altitude conditions with a uvb reptile bulb plus i live in Denver and the outdoor cannabis grown at 5280 feet above sea level is always bomb and weed from Colorado’s high country is even more potent so uv and uvb yes.

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