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  • Wuxi Kinglux Glass Lens Co.Ltd
  • ADD:No.286,Changjiang North Rd,New Dist,Wuxi,JS prov,China
  • Tel: 86-510-66759801
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  • Contact person: Huimin Zhang
  • Selecting COBs
    Mar 26, 2018

    Selecting COBs

    Popular Models

    When it comes to COBs for indoor growing, the majority of people are currently using 1 of 3 proven brands: CreeCitizen, or Bridgelux. In my opinion, if you’re looking for low-current efficiency and aren’t overly concerned with cost, go with the Crees. If you’re looking for a good all-around COB that’s easier on the wallet, or intend to drive your COBs with more current, go with Bridgelux or Citizen. The new gen. 7 & SE Veros and Version 6 Citi’s are really closing the gap in terms of efficiency, and can be found considerably cheaper (here in Canada, anyway).

    • Currently, the most popular COBs from Cree are the CXB3070 and CXB3590 models, with the 3590s being the best Cree offers for this application. The 3070 is a good alternative, and, while not cheap, is less expensive than the 3590.


    • The Bridgelux COBs used by most indoor gardeners are from the Vero Gen.7 or SE Series. There are 4 different sizes in the Vero series: Vero 10, Vero 13, Vero 18, and Vero 29; the number reflects the size of the Light Emitting Surface. Of these 4,  the 18 and 29 models are most popular. While these COBs are not as efficient as the Crees, they still put out a lot of light (at higher currents) and are significantly less expensive.


    • The Citizen COBs that most growers are using are the Version 6 CLU048  units. They come in a few different configurations like the CLU048-1212 (contains 12 diodes in parallel and 12 in series) or the CLU048-1818 (18 in parallel, 18 in series). There is also a larger model which runs at a considerably higher voltage but puts out a ton of light: the CLU058.

      Important Specifications

    Aside from cost, there are a handful of important specifications that you’ll need to consider when choosing your COB. I suggest you read through the points below, then when you have a better understanding of these few specs, read this post on how to easily compare COB LEDs using manufacturer-provided simulation spreadsheets.

    Colour Temperature (also referred to as CCT or Correlated Colour Temperature)

    Measured in Kelvin (K), colour temperature determines how warm (red) or cool (blue) the light emitted is. Lower values (e.g.- 2700K) are warmer and higher values (e.g.-5000K) are cooler. When using LEDs to grow plants, we’re mostly concerned with the “PAR” range of light, which stands for Photosynthetically Active Radiation. PAR represents the range of light that plants use for photosynthesis (wavelengths of 400 to 700 nanometers), and it’s in our best interest to use colours in this spectrum.

    It’s up for debate whether it’s better to use different coloured lights for different stages of plant growth – some say that 5000K lights are best for the vegetative growth phase, while a warmer light (2700K-3000K) is better for the flowering phase. Others argue that a middle-of-the-road temperature like 3500K works for both phases. My first grow of tomatoes, peppers, and herbs was done using only 3500K lights, and they performed nicely all the way through. For simplicity’s sake, I’d recommend going with 3000K or 3500K for the whole grow.

    Below is an example of the Spectral Power Distribution for different colour temperatures of the Cree CXB3590, obtained from the product datasheet. You can see that higher colour temperatures (4000K and 5000K) have considerably more output in the ~450nm range (blue) compared to the ~700nm range (red). The reverse is true for lower colour temperatures.

    Forward Voltage

    In the interest of keeping things simple, I recommend wiring your COBs in series(unless you have a whole whack of them running off of a small number of drivers, in which case, you might need to do a combination of series and parallel wiring). The voltage of the COB is important, because when wiring in series, voltage is added, while current remains the same. This is the opposite of parallel wiring, where voltage is the same through every COB, but current is added up and varies. For a more in-depth look at series and parallel wiring, check out this post.

    Continuing with our Cree CXB3590 example, you’ll note on the datasheet shown below that there are 2 versions available:  a 36V version and a 72V version. Let’s say you opt for the more common version which has a typical forward voltage of 36V. If you decided to run 2 of these 36V CXB 3590s together on 1 driver, you would need to buy a driver that outputs your desired current (I’ll get to this next) at 72 Volts (36V Cob 1 + 36V Cob 2 = 72V total).

    A caveat to the typical forward voltage is that at different levels of current and heat, voltage will change slightly. For example, viewing the graph below, you can see that when you run a 36V CXB3590 at 1,400 milliamps (a common drive current), voltage will not be 36V, but somewhere between 34V and 35V. When the same COB is run at the maximum allowable current of 3,600mA, voltage is up above 37.5V. These small changes may not seem important but it can make a difference when you’re looking to squeeze multiple COBs onto a driver that operates in a particular voltage range and need the total voltage at each COB to be a few volts more or less than typical.

    Forward Current

    The maximum forward current rating lets you know the largest amount of current you can apply to the COB. Referencing the chart above again, the maximum forward current for the 36V version of the CXB3590 is 3,600 milliamps.

    Common drive currents used for COBs like this are 700mA, 1,050mA, 1,400mA, 2,100mA, and 2,800mA.

    As you increase the current, you receive diminishing returns in terms of light output – more and more power is dissipated in the form of heat, rather than photons. For this reason, it’s always better to buy more lights and underdrive each of them if you can afford it. Though it’ll be significantly more expensive upfront, your system will be more efficient and will save energy in the long run.

    As mentioned, when wiring in series, the forward voltage drop of each COB is added and current through the entire string remains the same. For example, if you take 4 CXB3590s and wire them in series to a 2,400mA driver, you have a total voltage drop of 144V (36+36+36+36), but every single one of these COBs will get the full 2,400mA of current.

    Efficacy

    Efficacy refers to the number of lumens the COB produces per watt of power. As discussed in this post on methods of measuring light, lumens are not the ideal unit of measure for horticultural applications (PPF or PPFD are), but they still serve as a solid way to compare one COB versus another. Efficacy is not to be confused with efficiency, which refers to the percentage of electrical power that an LED is able to convert to photons vs. the percentage of that power that’s wasted as heat. Efficacy won’t be listed in the data sheet, but can be easily obtained. Check out this guide on comparing LEDs to learn how to determine a COB’s efficacy.