CMH is the new bad boy of the indoor growing scene.


CMH is the new bad boy of the indoor growing scene. More efficient, cooler, brighter, and more cost-effective than their predecessors, CMH lights are quickly taking the industry by storm. As with any new technology though, there are some general misnomers and misconceptions about what CMH actually is. We’re here to teach you the ins and outs of CMH lighting and why it’s the new favorite among professional growers.

What is Ceramic Metal Halide?

Before we get to the benefits of CMH, let’s talk about WHAT it actually is: CMH stands for Ceramic Metal Halide and is sometimes also referred to as ceramic digital metal halide (CDM) or Light Emitting Ceramic™ (LEC™). As we mentioned in the opener, there are still some general misconceptions surrounding CMH, which is mostly due to our shorthand aliases, and in particular LEC. Notice how we have the little “TM’s” next to our first mentions above? This is because LEC is actually a trademarked brand of CMH lights. That’s right – LEC and CMH are the same thing!

Ceramic Metal Halide Grow Light Setup

Now that we’ve cleared that up, there’s another thing growers get hung up on sometimes – the new and exotic PGZ18 base. This odd-looking base is locking bi-pin type as opposed to the traditional US mogul screw. The PGZ18 base is sometimes mistaken as ceramic metal halide identifier, mostly because the first CMH bulbs suitable for our application went mainstream in Europe where the base type is more common. While traditional screw base CMH lamps were the first to arrive on the US indoor garden scene, the PGZ18 eventually made its way here, and hence, the confusion began.

If CMH and LEC lighting are the same thing, and ceramic metal halide bulbs/lights can have both PGZ18 and mogul bases, what’s the difference between CMH and a regular metal halide? Well, the short-and-sweet of it is – it’s all in the arc tube. Metal halide lamps have been around for a little while now, and CMH is basically a new extension of that technology. Whereas normal metal halide lamps use quartz or PCA (Phosphorus Converted Amber), CMH lights use a ceramic composite for their arc tubes. This allows the filaments to burn hotter, creating more and brighter light than standard metal halide lamps.

So how can we identify a CMH arc tube? Our lineup here shows a few popular CMH bulbs alongside an HPS and a standard MH bulb for comparison. In the image, we can see that HPS arc tubes are long and cylindrical while MH is more pillow-shaped and pinched on the ends. By contrast, our CMH bulbs feature a bulbous arc tube that tapers off into a thin tube on either end. Although there are some slight differences, CMH arc tubes all have a similar design. Notice also that we have CMH bulbs with both the PGZ18 and mogul screw-type bases.

Advantages of CMH

As responsible growers we’re always looking for ways to improve efficiency in the garden, and in terms of lighting, CMH helps us do just that in a variety of different ways. This is why more and more growers are making the switch. Let’s take a closer look into what’s at work here:

CMH Spectrum: High-Pressure Sodium (HPS) has been our long-time favorite thanks to the tremendous amount of light it produces. Truth is, HPS really does pump out the light, albeit not that efficiently. Ceramic metal halide bulbs are able to produce a much more efficient spectrum in terms photosynthetically active radiation (PAR) light, and this again goes back to the CMH arc tube. Ceramic arc tubes are capable of burning hotter which, in turn, allows the combination of different halides that produce a better growth-oriented spectrum. And this is true not only for the blooming phase but for the full growing cycle, which makes CMH a legitimate full-cycle lighting option.

In our spectral distribution charts of the Philips MasterColor ceramic metal halide bulb varieties, it’s easy to see how broad range of the general CMH output correlates to both ends of the PAR range. These characteristics allow ceramic arc tubes to do more with less in terms of PAR light output, which is why growers are often able to replace higher wattage lights with the more meter-friendly CMH.

Beneficial UV light: Industry-wide research has also conclusively shown that plants do benefit from exposure to UV light. Specifically, UV-B light which is present in natural sunlight and deficient in most other traditional indoor grow lighting sources. UV-B has shown to have positive effects on the creation of essential plant oils especially. Traditional MH and HPS lamps don’t put out any significant UV-B light but CMH lamps produce amounts (as can be seen in our spectral distribution charts) that are conducive to healthy, more natural plant growth.

CMH Lifespan: A lamps serviceable lifespan in the indoor garden is really tied directly to lumen/intensity-maintenance, which is again related to the arc tube. Along with expanding spectral formula options, the more robust CMH arc tube also maintains output at an acceptable level for almost twice as long as standard HID varieties. This allows CMH growers to enjoy a lower frequency of bulb replacements vs. those using HPS and MH lamps.

Accurate CRI: While CRI isn’t connected to growth results, using a light source with a high rating can help in other ways. So what exactly are we talking about? The color of a light directly affects your ability to see the color of things under that light: this is called CRI, short for Color Rendering Index. The CRI rating of direct sunlight is 100, which means that colors are shown with 100% accuracy when viewed under the midday sun. While CRI is connected to the Kelvin scale, it serves a different purpose altogether as a non-growth-related metric. In the Kelvin ranges seen here, it’s easy to see why the middle range (where CMH falls) will have a higher CRI than the edges where HPS and standard MH lamps generally fall.

This isn’t always a problem, but if you’ve been around many indoor gardens, then you already know how these different lights can make plants look. High-pressure sodium lights have a CRI rating of only 20 – they put off such a heavy yellow cast that everything under the light just looks yellow. While plants grow fine under HPS, this can make it really difficult to spot plant health issues because they usually turn a yellowish color when there’s an issue (and if everything looks yellow under your light, nothing stands out).

So, before moving onto system options let’s recap CMH:

  • CMH, LEC, and CDM all refer to ceramic metal halide (same thing)
  • Bulbs are made with both PGZ18 and mogul (screw) base types
  • Provides a balanced spectrum suitable for full-cycle growth
  • Produces beneficial UV light · Lasts twice as long as standard HID (MH/HPS)
  • Makes the garden look natural

The Best CMH Lights

It’s pretty clear why growers are switching to CMH by the droves, and it doesn’t look like this wave is about to break anytime soon. Now that you know why you need to upgrade, what light should you buy?

As with most other aspects of growing, the best option, or best CMH light in this instance, really comes down to what will work best for your unique indoor garden. There are now many fixture brands and styles to choose from including integrated fixtures and remote systems that feature a design similar to traditional HID grow lights. All-in-one or integrated fixtures like AgroMax HyPAR and Sun System LEC 315 will work great for most situations, while systems like the HyPAR remote CMH might be better if you tend to have heat issues. The remote option allows the ballast to be located outside of the grow tent or grow room, which reduces heat. Further, these lights can also be used with a sealed reflector and integrated with ventilation to further control temperatures.

If you need some extra power, i.e., planning to replace 1000w fixtures, the dual-lamp varieties would be your best option. These fixtures are often referred to as 630w CMH grow lights, which can be a little confusing because the wattage indication here isn’t directly tied to the bulb like it is with HPS and MH. Instead, most 630w CMH lights like the Digital Greenhouse dual CMH and the Sun System LEC 630feature two sockets that run 315 CMH bulbs – hence 630w.

315w CMH vs. 400w CMH

Beyond physical differences and single/dual lamp capacity, one of the other main considerations in choosing a light is performance, and there is really only a thin line of separation there among the better units in terms of growth potential. While the 315w CMH systems like the Sun System LEC are perhaps the most popular fixture type, even one of the cheapest CMH grow light systems, the HTG 400w CMH is a solid option. The main argument in favor of 315w lights here is that 315w lamps like the Philips offer a superior spectrum vs. the GE. While this may generally be the case, the thing to remember is that the GE offers a 20% higher output (initial lumens – 33,000 vs. 41,000) with a very similar spectral distribution as seen here.

With performance being so comparable between light models, the only thing left to consider is budget. As stated earlier, one of the main goals for switching to or buying CMH is the efficiency factor, and to this effect, growers who have long-term cost in mind might gravitate toward 315w units in hopes of making up savings on the power bill over time. While it could end up saving in the long run, let’s take a quick look at the math to see how it shakes out:

315w CMH vs. 400w CMH Cost Comparison

Admittedly, we are using one of the most expensive lights to illustrate this point, BUT it takes a while to make up even a $100 price difference at $8.56 per grow cycle. Plus, this example assumes that you’re grow is a finely tuned operation capable of pumping out (5) 10-week grow cycles per year!

So, when comparing among single-lamp CMH grow lights, the takeaway is this:

If you don’t care about cost and you just want the lowest wattage light, go for one of the top 315w units like the HyPAR or LEC 315. If you’re just getting started and/or growing for a hobby, consider the HTG 400 CMH or one of the lower priced all-in-one units, which will provide comparable performance. You can even go with a CMH conversion kit if you have an existing HID system. Whatever setup type you opt for, you can’t go wrong with CMH!


If you use a CMH grow light in your setup, throw a picture on Instagram and tag us in it (@HTGSupply) – we’d love to see your results! And don’t forget to check out this week’s coupon code and sale information below! From all of us here, good luck, stay safe, and Happy Growing!


Enter this week’s promo code at checkout for a 10% discount on any CMH grow light including the products featured below, or visit your local store and simply mention this article to get the deal! Thanks again for tuning into Talking Shop with HTG Supply!

Offer valid through and in-store 11/10/17-11/17/17. Cannot be combined with other offers.

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