CMH or LED's: Which is better for your garden?
Is one better than the other? CMH grow lights and LED grow lights aim to give your plant every bit of the light spectrum it needs without wasting light (kind of like HPS bulbs and some T5 fluorescent lights try to do). Here, we'll be going over the advantages of both CMH's and LED's to get a better idea of what should be in your grow room.

Light Temperatures and their Affect on Grow Room Temperatures

To start things off we'll discuss the temperature these lights give off. We've all heard that LED grow lights put out much less heat than HID's, which is true. But have you ever wondered why that is?
LED's are electronic, and truth be told, the majority of the heat that comes from an LED is not from the actual diode itself. Heat is mostly generated from all the parts running inside of it: the ballasts, motherboards, fans to cool it all down, etc... In all fairness, wires and chips inside diodes will give off a little heat. That's why the lights will be warm when you run them at high wattages for a while. However, even the strongest LED's don't get anywhere near as hot as HID's. Unlike LED's, HID grow lights work because of gasses, not wires or chips. The type of gas and chemicals used in HID grow bulbs- like mercury and metal halides- react with each other to give you light. As the bulb gets brighter and brighter, it gives off heat. That heat is pretty intense and will radiate from the bulb. The higher the temperature and the longer you run it, the hotter the bulb and your grow room will become. Now, it should be noted that CMH's run in the same way standard MH's run, only they have ceramic bases. However, ceramic metal halide bulbs run a lot cooler than MH and HPS bulbs by about 8°F. An LED ran cooler than CMH's by at least 2°F, and overall 10°F lower temperature from a higher-powered LED. (*Note: LED's range in wattages and structure. Different lights will produce more or less heat.)

Spread and Intensity of Light

In this test we've taken a Yield Lab 400W HPS+MH Air Cool Hood Reflector Grow Light Kit, the Yield Lab Professional Series 120/220v 315w All-In-One Hood CMH, and a King COB 360 Watt Professional Series High Coverage COB LED Grow Light and tested them on a 4x4' grid with a PAR meter to see how intense a light is.
Comparison of par charts with different kinds of lights
The numbers you see are readings of intensity based on a point on the grid, with the most intense, focused light in the middle and lower intensity as the light spreads. Now, the 400w HPS light was hung at 18" and you can see that its maximum par sits at 534, which is pretty good. However, the 315w HID at 36" above the plant, its max par was 608- that's a 74 PAR intensity increase at twice the height! When we hung the 360w COB LED at 36" and found the max PAR at 538. That may not seem like a huge jump, but again: keep in mind that you're getting more intensity at twice the height, which out-performs the HPS no problem. Knowing that the LED and the CMH blew the HPS out of the water, we compared the PAR of the CMH and LED's, and found that the CMH was more intense than the LED we used by a PAR reading of 70. Between these two lights, it looks like the CMH's will give you a little more intense coverage than LED's (of similar wattages, of course).

Light Spectrum

CMH and LED grow lights are known for one thing: giving your plants the spectrum of light they need to grow the best plants around. They do that by pinpointing specific wavelengths of light and giving those to your plants. By doing that, these types of light try to give your plant everything it needs and nothing it will waste.
CMH’s do that by giving your plants a spectrum of light that covers the entire light spectrum. Unlike MH’s that give you cooler blue spectrums for vegging, and HPS’s that give off warm red spectrums, CMH’s tend to amplify the orange and yellow spectrums right in the middle of the light spectrum. Doing this gives your plants a more natural, even lighter than other bulbs. LED’s, on the other hand, are known to give your plants very specific wavelengths of light to stimulate stages of growth. For example, you have all red LED lights that stimulate flowering, all blue LED’s that are great for vegging, and LED’s with blends of different colored diodes to cover the entire spectrum of light. With mixed LED’s you get a purple glow down on to your plants, but that light contains all the wavelengths needed to grow- no more, no less. Well, that’s unless you have newer LED’s that contain UV and IR diodes to give your plants stronger branches and more resins. There are also LED’s that give off light similar to a CMH’s for growers that don’t want that purple light in their grow room.

The Final Results

We know that both CMH and LED’s have their advantages and disadvantages, yet they’ll give you awesome harvests. Through it all, though, there’s still one factor that seems to stand out from them all: cost. LED’s are great at getting your plants where they need to be (and then some), but the problem is they’re expensive. Add to that the number of LED’s on the market, and it can be hard to tell which LED’s you need, what spectrums will work for your plants, and most importantly, what’s the best value for your money. CMH’s, on the other hand, is far more cost-effective than LED’s. Sure, you may have to combat heat eventually, but compared to the output of an HPS or MH grow light, you’ll still be saving money on in the long run compared to other lights on the market. At the end of the day, you’re going to have to spend money on a grow light. CMH’s are better priced for personal grows as well as warehouses, and everything in between. Given their even spectrum and their relatively low price, they’re worth getting. Now, that’s not to say LED’s aren’t worth their costs. Though LED’s are the most expensive lights around, LED's are more intense than HID’s which can give them a performance advantage. However, if you’re not familiar with how strong or different they can be versus HID’s, you might be in for a rude awakening when plants don’t grow like they used to. That’s why we recommend CMH’s for nearly any grow out there: they’re cost-efficient, give you a great spectrum, and are pretty easy to use. We recommend LED’s for seasoned growers who want to take their skills even further, who also have the space to grow with LED’s (you’ll need to hang them higher than CMH’s, so make sure you’ve got the room).



We’ve tested both the Kind LED grow light (great light) to the Advance Spectrum MAX and they’re almost identical in terms of PAR value and output. Biggest difference is that the Advance Spectrum MAX LED Grow Lights have a UV spectrum which helps greatly in resin production.


My best choice would be LED Grow Lights only because i am a very busy grower and LED lights get the job done for me when i cannot manage all too much. Great idea on this.

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