COB LED Lighting


I just wanted to provide a place to discuss LED Lighting, primarily the differences between diodes (Lights with a purple hue) and full spectrum COB’s (Appear to be “White” light).

Here is a list of definitions of all the primary Lighting terms:

LEDs are very complicated when it comes to calculating the actual amount of light usable to a plant. From a DIY point of view I can’t imagine trying to build my own LED fixture using 50 diodes. A single COB bulb makes it very easy to build, this one light got me started growing for $40. and with 5 you can easily illuminate a 4x4’ area for $200.

I will say there is a newer CXB3590 Bulb by CREE now tops out at 300 lumens per watt, which is very impressive given where they were ten years ago:

Here is the CREE CXB3070 COB LED installed onto a heatsink:

I find that CPU coolers are extremely cheap to find because there are so many on old computers, they tend to be more than sufficient to cool the bulb (100-200W active heatsink). I can say that the lights are capable of growing 4" California Sweet Peppers which require a full spectrum, as well as high intensity lighting to actually create large peppers. They operate at 36V and are capable of 100W, but to get them to be more efficient I only drive them at about 1.4 Mamp. This allows me to have it run at almost 66% efficiency in terms of output.



LED Driver:

If you all are interested in learning more about plant lighting requirements, I highly suggesting reading this article:

If you all are interested in learning more about LED lighting calculations, this article is very comprehensive:

Custom LED Light Panel FCV2.0
Alternative Hardware for DIY Food Computers
Minimalist Growing
Data Model Exercise: Cornell Hydroponic Lettuce
Complete design of the personal food computer (and possible alternatives of some components)
MVP - Product Design
Discussion on the aptness of the light sources used in PFC
Building, growing and designing in Riggi's "garden"
Brain_box build for Research
Minimalist Growing

You all are stuck on using and thinking Lumens and lux. The only part of the entire global radiation spectrum which can be used by a plant for its photosynthesis is between 400-780 nm, the PAR-light (Photosynthetically Active Radiation). The shorter wave lengths close to 450nm, are used by the plant for fast growth, while the opposite end of the PAR near 650nm, is needed for strong flowering. Approximately 45% of global radiation is PAR light. The amount of photons in the PAR region is called growth light (indicated in micromol (μmol)). Providing only nm range to the plant is a world of difference from simply giving the plant white light. You must know what global radiation length (color) it is producing (indicated in nanometers (nm)) and how much, (indicated in micromol (μmol)). I just got my received my new par light meter from Spectrum Technologies this morning along with a DLI (daylight intragal). The Dli meter gives me a micromol (μmol) count. Relieved over a 24hr period. I have been using white light fro the last few years and thought I knew what was going on. The difference from the same wattage white to blue and red, i find close to half. As of today I have reanalyzed my plans, entirely. I have seen a whole new world of light.
invest 200$ and you will know a LOT LOT more about what you are making.
This is my site that i use for personal use to make notes. I used to design web sites so it came natural to me.

LEDs for food server

I’m not sure why you would say I am stuck on focusing only on lumens and lux. The reason I address it is that I understand that is the only unit of measurement that most people understand currently. If you read my final article I post it actually gives a very detailed explanation of how to calculate your own PPFD by knowing the lights SPD and current lux output. Because I build my own lights, I always know those details and so I am able to calculate what my output will be based upon a calculator I have built.

I would be curious to know what type of plants you are growing, and what lighting you have chosen to use based upon the expertise you have gained with your sensor.

Sensor Data Modeling

I’m in the process of specifying a LED system for watercress.

I tried some smaller COB’s without much success (intensity may have been too low)

Based on looking to emulate the light spectrum of the best Umol/ Watt on the market

Which seems to be BML’s ‘Grow Max’

It seems to be all about the Red at 660Nm

I also found this guide which suggests white / 660 Nm red is the way to go. (Due to the fact that ''white" Led’s are actually blue LED’s with a phosphor coating)

Is this what other people are thinking too? What else should I read?





Good morning,
I thought I would weigh in on this topic. Lets start with the CXB3590 by Cree, COBs certainly have their place in lighting and agricultural lighting but for specific uses. First lets look at the lm/w, which I agree are not the correct units of measure for plant growth, never trust Cree’s advertising you have to look at the datasheet! The CXB at 3000K (spectrum speaking a good starting point for plant growth) driven at 36V 2400mA yields 86.4W and hot-binned (once the LED is warmed to 85C case temp) yields 11,000 lumens which is 127lm/W not 300 lm/w. This 127lm/W assumes one can keep the junctions of the COB at 85C which for such a small source is no simple task. Keeping this device cool requires a low thermal resistance path to ambient environment. The CXB is far from 66% efficient it is closer to 35%; given this efficiency 35% of the energy is leaving as photons and the 65% is converted to heat (86.4W)(.65)=56.2W of heat. If you start with an ambient temperature of 25C in order to keep the LED temperature at 85C you would need a thermal path or cooling system capable of 1C/W, which is not impossible, but no trite matter. Another design consideration for the COB is achieving a homogenous light pattern at the plant canopy. Light which does not strike the plant is a waste regardless of the uMol/W of the light fixture, and a single source COB with such a large LES is hard to shape in a homogenous manner, and very hard to change as your canopy changes throughout time. Albeit, designing a fixture with multiple LEDs is far more challenging then the COB path, but optically and thermally speaking there are some major advantages to this topology.

The last point I would like to touch on is a word of warning of trusting the quantum sensors mentioned in the previous post. Quantum sensors are an incredibly valuable asset to the would be horticulturist, but beware of the readings when not using sunlight. The sensors are designed for specific sources they are measuring, if you look at the sensors documentation they give different weighting depending on if the source is HPS, fluorescent, or Sunlight. The best tool for measuring the LEDs par value or PPFD would be a spectrometer. The spectrometer also gives the added benefit of being able to see the exact (or as close as you can with measurement) to which nm of light are being emitted.



First of all, thank you for your great insights, I really appreciate contributions from people who know what they’re talking about!

I want to clarify that I am by no means saying this is the best method to grow plants. I am however offering a solution to someone looking to spend under $100 and have the ability to grow plants through maturity.

I want to challenge you on what you said about efficiency being only 33%. Keep in mind I am not driving these COBs at their full potential, due to that, I am getting a much higher efficiency than if they were running full power.

When it comes to cooling, I found active cooling to be the most obvious choice because it simultaneously created airflow, this keeps my COB temperature below 40 C.

Sorry it took me so long to get back to you!

Bypassing PFC, straight to (mini) Food Server

You mentioned that you had a calculator for calculating the PPFD output of you lights, would you be able to post this? It would be great for comparing lights when building your own light fixture.


Sorry to take so long to reply, I just happened to see this.

My calculator only works for my lights because I already know the Spectral Power Distribution so I can calculate based upon that. Since your lights would be different from mine it would not really work.


Disclaimer: this video is focused on the growing of Cannabis. However, in my opinion, it is one of the best introductions to photomorphism & understanding how lighting gets even more complicated once we step outside of lettuce. UV & far red diodes are used to influence and shorten the days to harvest (in some cases by over a week).

If you’re interested in learning more about lighting and how it relates to plant science, this video is definitely worth it:

OpenAg™ Personal Food Computer v2.0 (beta) [Documentation Release]

Great series of lectures by Dr. Cheri Kubota at University of Arizonas Controlled Environment Agriculture Center. This one gives great overview of plants response to lighting, and really helped clear up some of the confusion I’ve had surrounding the significance of green light on plants (skip to 32 mins for that).


Awesome info. I’d like to use some for my site, very informative info.


@Webb.Peter, I’m starting to see more and more COB Leds showinig up in things. I really like them. Do you know of any large COB Leds that are RGBW controllable? I’ve been getting back into electronics recently and i’ve been playing around with NeoPixels from Adafruit. I love them! I just added the NeoPixels to my DIY hacked breadmachine incubator. The incubator is mostly designed for biohacking / home microbiology bacteria petri dish growing, but it can serve double duty as a seedling sprouter / incubator. The RGBW Neopixels are great cause i can use them mainly for white lighting to see inside but with the flick of a button i can change them to blue/red grow lights or blended purple or pure red or pure blue. I am interested in something similar on a larger scale for my future food computer build as the RGBW leds would come in handy for growing / breeding with plants that are adapted to growing in South America and do not flower or set pollen in my temperate Colorado climate until late fall when the light gets less frequent and shifts into the red spectrum. This has most notably been an issue when i’ve been working with Teosinte from mexico. I’d love to have a large food computer that i can easily manipulate the light to trick Zea diploperrennis into silking and tasseling early to cross with modern Corn/Maize for perennial Maize investigation / experimentation.

There are other plant varieties other than teeosinte, but this is the one i have the most experience with this issue.



Great convo going here, thanks all for the info and resources. I’d like to share my experience first, then explain my take on applying semiconductor light sources to horticulture using market ready technology. I’ve built several types of LED and hybrid fluorescent+LED fixtures and it appears we all agree spectrum and photon concentration (delivered to the canopy) are key variables.

COB arrays with single/mixed spectrum emitters are manufactured in many flavors. In my experience, the packages sold form Chinese distributors (ebay, AliExpress) work but they’re prone to manufacturing and design defects that reduce efficiency and lifespan. COBs manufactured by known manufacturers and sold by reputable distributors cost more, especially driver-less versions. Mixed spectrum COBs usually do not allow for independent channel control so you get a set spectrum output with the only control being overall intensity of that set spectrum.

Great cheap COB comparison
Mixed emitter COBs with independent channel control (mouser)

Like most commercially available lighting fixtures, COBs pack as much output as they can into a small package to reduce manufacturing costs. This makes sense from the manufacturing side but single source fixtures result in a greater concentration of heat and a greater dependency on a single point of failure in a single package setup.

Although I see great potential in COBs, I’m still rocking 3W/5W combos in my arrays. The two main reasons are:

  1. Due to the inverse square property of light intensity and the potential benefits of oblique spectral radiation (side lighting), I like my light spread out and close to the canopy. COBs mean concentrating radiant energy from fewer sources which are on average farther from the average vegetation. Implementing light in a more modular way can also increase the reliability and fault tolerance of the array - you avoid a single point of failure.

  2. Because I’m isolating the color spectrum through independent emitters, I get to control the spectrum completely by swapping fixture plates with a different mix of emitters. In theory this has limited adverse effects on total output or efficiency because I’m not forcibly dimming emitters that remain in the array. When you invest in a fixture that concentrates high power light sources, you’re stuck with that spectrum and in a concentration that imo is difficult to optimize for plants. Compounding this potential issue, full spectrum emitters (like the Cree above) emit good light energy in an arguably less useful spectrum (green/yellow).

I’ll continue to integrate COBs into my arrays as the price for low-watt packages (10-30W) decrease and the quality increases. As a tool for in-depth experimentation I see COBs as playing a supporting role to other spectrum specific components.


I decided to buy one of these to play around with. I also put in an order for some WS2811 chips to tinker with as well. The WS2811 chips are the same ones built into the Adafruit Neopixel RGBW LEDs, so i will tinker around with seeing if i can make a large COB “neopixel” with one of these chips and some transistors or something just for experimentation sake.

Though i do like what @Drew said in the last comment. In the same order as the WS2811 i tacked on a 5W RGBW led and a 10W RGBW led!. Though not COB i don’t think, still 10W in a tiny RGBW Led sounds awesome! Will be tinkering with them as well. Who knows, maybe i can come up with a small modular PCB that has 4 10W Leds each and is easily linked to new boards via a header or something. It would be easy to then go from 40W to 160W easily. Though of course your power supply and heat dispersion would need to keep up. Just an idea at this point.



Wow! Thanks for linking the video. Glad to learn more about the utilization of green light by other than chlorophyll such as cartenoids.

I’d love to see a graph about the light utilization of anthocyanins (purple pigments). Many of the vegetable and plants i work with and/or breed tend to contain high amounts of anthocyanin expression. I tend to think the plants with this adaption do better in my climate. I live at high altitude so the air is thinner here and more UV radiation gets through. I suspect the anthocyanins can act as a sort of sunscreen for plants. For many seed varieties that are bred in greehouses on the east coast or somewhere in Califronia etc. usually die a miserable death in my climate when introduced for the first time. I think it is due to a combination of factors including dry air, high altitude high sunlight, etc. But heavily adapted varieties are key to success and survivability where i live.

Plants with anthocyanins theoretically should be able to survive in environments with higher UV exposure (i.e. Mars?) and also in colder environments. Anthocyanins also convert some light into energy but are less efficient than chlorophyll. The tradeoff is that at low temperatures where chlorophyll is not able to function anythocyanins are able to function and sometimes can help a plant to survive cold temps when many crops or plants would die or go dormant for the winter. This is my theory anyway.


Great discussions! I wanted to share some articles I found recently regarding this topic:

“Current thinking, however, centers on lighting that can deliver peak energy in the blue and red spectrum but that also delivers a broad spectrum much like sunlight. Paul Scheidt, LED product development leader at Cree, said, “The industry seems to be moving more to white light.”

@Drew I’m interested in your opinion on GE Bright Stiks. We use them in the $300 Food Computer - MVP BOM. Are you aware of any other extremely cheap sources for plug + play COB full spectrum lights? I’d prefer to have it in a wider distribution than 4 arrays of COBs, but can’t beat the fact that it’s a lighting solution for less than $20.


I found some awesome in-depth videos on this YouTube channel about DIY lights with COB LEDs.

Grow lights are without a doubt one of the most difficult things to choose, so much speculation and it seems like everyone has a different theory! Personally, I have really liked the VIPARSPECTRA 300W and 450W they’re mostly red and blue with some amber and white, IR as well if you’re into that, they can also switch between veg and bloom for more control. I have them 4’ above my plants and they have still been great, they don’t have the best penetration when the plants get tall but otherwise they’ve been awesome. I think you could maybe fit the 300W inside the PFC 2. They come with a 3 year warranty too which is a great bonus.

I’m a big fan of this style of LED light in general because the heat from the power supply stays inside the enclosure and does a really good job at keeping it warm. Plus that purple glow :heart_eyes:

There’s also that ~$30 one from the PFC 1 that I played around with a little bit, its not bad and definitely a win for the price.


Could you post some links/pricing on these? Do you have a way of measuring their output?

Growmau5 is MY FAVORITE! I posted one of his videos earlier in this thread: COB LED Lighting

He actually was nice enough to help me when I was first getting started building these COBs a few years ago. My #1 recommendation for anyone out there interested in getting into DIY COB LEDs is to watch this series:


Yes sir! Here’s some links, I have tested both:

This is the 450W which does have the veg/bloom switches

This is the 300W which does not switch, but still does an exceptional job.

Here are the PAR and spectrum goodies: