The Cannabis Grower’s Guide To LED Grow Lights: Lumens

LED Grow Lights Lumens

One of the most commonly used terms when referring to the power of a given grow light is the word lumens.  For years, it has been the standard measurement of the growing capability of metal halide and high pressure sodium grow lights.  The problem is that this term has been used incorrectly for over 30 years.  In this article, we will explore the real meaning and correct use of lumens and further describe what you should be looking for when it comes to choosing LED grow lights that pack the most growing-power for your dollar.

What are Lumens and Lux

Lumens and lux are both measurements popular with grow light manufacturers - both HID and LED - to give potential customer a reference point for the relative brightness of various lights. In some jurisdictions, a lamp's lumen output rating must be on the label as required by law. What we are told (and have been for years) is that the higher the lumen rating of a given light, the better, faster, bigger, etc. your plants will grow.

But there is one MAJOR problem with using Lumens as a reference point for growing plants.

By definition, a lumen is a measurement of how bright (the power) a light is perceived by the human eye. The term lux is very similar to lumen in that it measures the intensity of light, however, it also takes into account the total area covered by a given number of lumens. For now, don't get bogged down by the technical side, just know that lux and lumen both measure the intensity of light to the human eye.

So what's the big deal? A bright light is good, right? The sun does a pretty good job at growing things and it's really bright. Don't we want to mimic the sun?

Well, yes and no . . .

Lumen & Lux Are Irrelevant To Plant Growth

Unless the plants under your grow lights have eyes, lumens & lux make zero difference in how well your plants grow. Plants respond most efficiently to light that is beyond what humans can perceive so it does not necessarily matter how bright your light is. As a matter of fact, 80% or more of the light emitted by either the sun or from HID lights, goes unused by plants for photosynthesis.  It is that portion of light that we humans see with our eyes and can register as being bright.

What matters most are the wavelengths of light that your grow light emits. When an LED grow light manufacturer rates their lights based on lumens, it is flat out misleading and irrelevant. Some manufacturers realize that people are starting to learn about this and are now skipping the word "lumen" and just showing pictures of how bright their light is. The result is the same - a bright light does not guarantee big yields.

Choosing An LED Grow Light For The Right Reasons

Making an investment in LED grow lights is nothing to take lightly. There are many factors that, if considered carefully, can almost ensure big yields. But you must take the time to educate yourself and explore the manufacturers claims. You best bet is to be sure the lights you buy come from a manufacturer that offers not only a warranty against defects but a guarantee that, if you don't like the results, you can return the lights for a refund.

Be sure the light you choose covers the correct spectra and offers an appropriate amount of power for your specific grow operation.  This article is only part of a multi-part series about growing cannabis with LED grow lights.  Come back often for updates and don't hesitate to contact us for help if you need it.

{ 21 comments… read them below or add one }

eric February 7, 2011 at 9:22 pm

I’m interested in building my own panel from a kit or scratch. any info would be apreciated.

HydroMan February 8, 2011 at 7:16 am

Eric –

To the point – don’t do it.

Unless you just want to build one for the fun or challenge of the project – then go right ahead. However, if you are trying to better the designs that are already out there or are trying to save money, then don’t bother. Trying to get out of it on the cheap will compromise your grow and likely leave you with poor results. What this means is that, whatever $$ you may save by building your own LED grow light, it would be wasted due to low yield and grow quality.


Hyalus February 16, 2011 at 9:12 am

I love this site and it has educate me greatly with th little information they have. So far I have been able to build a veg light(I have access to factoy that poduce them), now I am trying to trake down the correct nm’s and ratio they should be compared to the others bulbs.

Any information on this woud def help out.

Hydro Man I think I have talked to you before on another site. I dont think you are on that site anymore. If your the same person I would love to pick your brain.

HydroMan February 16, 2011 at 1:54 pm

Hyalus –

Good on you for trying to build your own – though usually you can pick up a decent light for the same price or cheaper than building your own. As for the correct wavelength’s and ratios, I would think that the factory you get your diodes from would be able to help you out if they have done any research. You can check out the various manufacturer’s websites as they publish this information but be warned. Many, if not all of them, do not publish ALL the info about their lights as this is proprietary information (i.e. trade secrets).


Hyalus February 16, 2011 at 2:23 pm

yes that i have came to relize. I know what diodes and wattage I want. I also know what view angles to shoot for. The quesion that has recenty been poppng into my mind is should I use different wave length per colour?

I am not sure if it was here or another site that said the bet way to fully utilize your wattage is having 2 different lights. Just like switchng out the bulbs on the mh/hps ballasts. Most of th led lights I have been seeing on the marke have a mixture of red,blue,orange and whites in them. I am thinkng this is because they were designed to be made for the full lifetime of the plant. In these I mostly see factorys using one wavelength per color.

So if I could find the perfect NM sequence I am sure I could ask them to build one at a fraction of the cost I could buy one for at retail.

Hyalus February 16, 2011 at 2:25 pm

ohh, but I do hear ya when talkin about those trade secrets. Any idea where or how to do research on what wave lengh (besides building a light of each and running them side by side) per type of plant is best?

I Married My Chevy Instead February 16, 2011 at 2:48 pm

Hyalus and Hydroman,

I recently started my first LED cannabis set up. Currently working with just coco fiber, which in retrospect is a terrible idea(not very efficient in holding or providing proper NPK’s and micros). The LED light i bought was off of ebay and was significantly brighter out of the box than it is now. Unfortunatly it came from hong kong and the specs are all jumbled up i.e, the recomended light hieght is 3 meters above the plant. Quiet possible that the 3 meter mark is in reference to growing something like lettuce as you said earlier.
My curiosity lies within switching my LED to something more powerful(higher watt’s per bulb, hopefully 3watt) and eliminating soil all together and going to aeroponics. I have heard that aeroponics is the cheapest most effeicent way to grow anything really, but i have not heard wether (fog) ponics is better than (misted) ponics. Personally i belive that the smaller the water droplet the faster the root can absorb it, clearly putting the fog system on top. The only down fall is murphys law(will it hold up to all of the nutrients, how will i be able to develop my fogging schedule, and what happens when your roots grow to large for the system and are in constant contact with water?)
In short i am shooting for a fog ponic, 3 watt per bulb LED setup for basicly 36 sq ft.
If there is any information you would like to share on those topics i would love to hear about it.

HydroMan February 17, 2011 at 6:42 am

Hyalus –

There are many lights on the market right now that use multiple wavelengths per color . . like the Magnum and the Illuminator and I think there are great benefits to doing that way.

As for researching a plant’s response to particular wavelengths – what you are talking about here is being able to quantify how a plant utilizes chlorophyll when influenced by discrete bands of light. This is what the good LED companies do and I can tell you it takes time and money to do research like that.

Good luck on your project,

HydroMan February 17, 2011 at 7:01 am

Chevy –

I feel for you getting stuck with some cheap crap! When you are ready to go for a new LED light, the one to go with is the 357 Magnum – a tremendous light and a big value given the output and price. Give Dave (owner) a call and tell him that Hydroman at sent you and he can help you determine the lights you need for your grow space.

Have you ever done a straight up hydroponic system yet? The reason I ask is that each step in hydro adds a level of complexity (hydro – aero – fog) that can be tricky on your first couple of grows. I feel that a fog system definitely has some merit but the technology is a bit too new for my liking – I would stick with either DWC or aeroponics for the main grow and, perhaps, add a smaller fog grow so you are not putting all your eggs in one basket.

One thing I recommend to ANYONE doing a grow, especially newbies, is this MMJ Grow Guide – huge, in depth, it basically pays for itself with your first grow.


great work May 17, 2011 at 5:33 am

from the short amount of looking into it that i have done, it actually seems cheaper to build it yourself if you have the know how and know a proper manufacturer, i havent pursued my own build yet as i am still researching manufacturers looking for the most economical yet dependable

i have taken notes though

the following come from a nasa study
12 red 660 to 6 orange 612 to 1 blue 470 was the best ratio they found for flowering plants at that time

the following also seem to be somewhat proven nms that are successful from other sources i have found

620 for orange/red

420 440 460 for blue

ive also found recently a newer led, at least it seems to be new, its in the farther red spectrum then 660, i believe in the 700s, that is supposed to also be very beneficial in addition to the regular 660s, ive heard people getting good results with equal ratios of 660 to the 700 one along with a few 620s and a blue

currently im only really focusing my energy on getting a flowering one down as the veg seems to be the easy part as far as lights go, yet there seems to be still alot of ongoing debate on flowering

personally i plan to make small “Test” lights where i can play with the ratios and size covered in a very small area then scale up from there

starting small it seems you can experiment fairly cheap compared to $300+ to test a commercial led light to see if it works for you

once you get the ratio, build or buy the larger equivalent setup to get exactly what you want/need

my plan is to 1st test the following ratio
12 of the high red in the 700s
12 of the red in the 660 like nasa recommended (this isnt an up to date nasa figure, it is several years old)
6 640
6 620s (also like the old nasa recommendation)
1 460
1 440
1 420

but again this is a hypothesis stealing from other proven specs and im still looking for the dealer to purchase the lights from, it also ignores the white leds and green leds for now until there is more information available about them

HydroMan May 18, 2011 at 8:40 am

GreatWork –

First off . . . if you really want to build your own light, you need to get some knowledge about how a plant actually uses light for photosynthesis – not just rely on these published numbers. Companies will publish *some* things and not others so you will have missing or untargeted light in your array. Second – forget about the old research (NASA) stuff . . .

What you need to research is photosynthetic pigments in plants (there are 6 primary pigments) and their corresponding action spectrum (the nm reading where absorption is at its peak for photosynthesis). These links will get you started:

Let me know if you need more help!

great work May 18, 2011 at 11:16 pm

You are the man
thanks again

peter June 30, 2011 at 6:56 am

GreatWork – how is it going with you led lights.?

James July 5, 2011 at 12:11 pm

What a great article i am in the LED Business and have been trying to explain that to my customers for years now. Our company is designing and manufacturing LED Grow lights and we do offer top quality lights with great warranty and money back guarantee.


funny July 21, 2011 at 11:29 am

can you tell me if the lighthouse 180w blackstar is a good led grow light and the led power is 120w, can you tell me what that will be in hps watts please.

HydroMan July 22, 2011 at 9:44 am

Funny -

I have heard very limited good things about the Blackstar lights . . . mostly negative reviews based on power failures and mediocre results. Watt for watt, it is probably comparable to at most 200W of HPS.


Zig October 19, 2011 at 6:35 pm

I just wish LED systems werent so expensive, Id love to replace my 2k worth of hps wattage. Anyone know of a good quality system good enough for 8×8 feet that wont cost me $1500?

HydroMan October 21, 2011 at 4:15 pm

Zig –

The short answer is NO. Your $1500 budget would be good for a 3×3 to a 4×4 space . . . check out the Magnum Plus or the 336x . . .

For true coverage of your 8×8, you would need a budget of $2500-$4000.


Jack January 20, 2012 at 4:51 am

hi im growing one plant and its small i was wondering would this do fine for growing one plant?
im fairly sure it is but im also confused about all the info you have got me reading.

i also have 8 25watt CFL 5000k currently for veg and i can use some of those to help it if its not good enough for a plant thats wont be grown for hieght but mainly for width in a small grow room
also this is cannabis.

HydroMan January 24, 2012 at 11:11 am

Jack –

That light would be HORRIBLE for pretty much anything . . . check out this article.

It seems like you are on a tight budget, huh? What I would do is stick with the CFLs – perhaps swapping out a couple of the 5000K lights for 2700K and running them together.


dave July 19, 2012 at 8:02 pm

How is it that Lumen and Lux don’t matter?
How do you measure the intensity of light hitting the plant?
Certainly not by watts, that’s how much energy is dissipated in the LED to produce said light.

By the way the human eye can see from 400nM ~ 700nM easy, so I would think Lumen is still a good measurement of how much light is getting onto the plant.

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