We have talked extensively about traditional HID grow lights and LED grow light systems, but there has been a recent trend growing with a 3rd grow light system you might not know about: Light Emitting Ceramic, or CMH grow lights that utilize ceramic metal halide grow bulbs. There are many perks to these lights with few setbacks. So let’s break it down:
Ceramic Metal Halide Grow Lights: A Break Down
Related: Growing Marijuana Indoors Guide 2018
CMH lights were actually introduced in the 1980s, but with recent discoveries in horticulture research, it makes sense why many growers are utilizing this technology.
The claim from CMH lovers is that your plants can enjoy a nearly full spectrum white light, very similar to natural sunlight that lasts longer than your HID counterpart. A CMH’s Color Rendering Index (CRI) rating is pretty close to the sun. CRI is a measurement of how true colors stay when the light is set upon them. HPS grow lights are 20 – 30 (that’s why it’s all orange/yellow in your grow room during flowering) while Metal Halides are 60 – 65 (which is why there’s a little bit of a blue tint in your growing area when you’re vegging). CMH grow lights come in with a CRI rating of 90 – 92 making them only 8 points off from our most natural source of light.
Right off the bat, once you turn on a CMH bulb at either 3,000k or 4,000k, you’ll notice a more natural looking light spectrum. No strong orange and yellow hues like an HPS bulb, or the bright white and subtle blues from a Metal Halide. Why is that?
Standard metal halide bulbs use a quartz arc tube whereas the CMH systems use ceramic, which lets the bulb get hotter in order to give you that perfect spectrum of light CMH’s give off. Not only that, but there is less degradation to the bulb because of the stronger arc tube material- that means they last a lot longer than other HID bulbs out there.
That’s why it operates at much higher pressure than standard MH bulbs. The ceramic arc tube combined with a unique mixture of salts and halides in CMH’s is what creates its broad spectrum. And in turn, gives growers the enhanced photosynthetic photon flux levels.
An added bonus to the quality spectrum is their lower heat output and power consumption. Lower watts means a lower toll on your electricity bill, and with lower watts, we also have lower heat.
One watt from a grow light creates four British Thermal Units (BTUs) of heat that need to be cooled. So in comparison, one 600w HPS grow light puts off 2,400 BTU ’s whereas one 315 W CMH grow light puts off only 1,260 BTU’s, which is almost less than half the HPS light.
With all that being said, with CMH lights your tent will be cooler meaning you have to run your AC less, again lower your electricity bill.
Putting CMH Grow Lights to the Test
Even at only 315 watts, CMH’s are stated to produce far more PAR in a grow area than a 600-watt HPS. But, these claims beg the question… how much better is a CMH than any other HID grow light?
We ran a couple of test inside a 4×4 reflective grow tent to figure it out. We hung several lights at the top and placed a thermometer right in the middle of the tent.
First, we ran the CMH light. The starting temperature was 74 degrees Fahrenheit. The CMH grow light raised the temperature to 86 Degrees. The inside of our testing facility raised to 77 degrees. So in total, the CMH raised the temp by 9 degrees in 30 mins.
Next, we tested The 600w HPS grow light. The starting temp was 80 degrees. The tent temp raised to 96 degrees. So the increase on the HPS was a total of 16 degrees.
As a bonus, we ran a dual 315 W CMH light and a 480 W Prototype LED grow light as wild cards. The starting temp on the dual CMH was 76 and increased to 100 degrees. The room temp raised from 76 to 80. So the Dual CMH raised the tent by a total of 20 degrees. When we ran the LED the starting temp was 72 degrees, and after the temp was raised to 82 degrees. That’s an increase of 10 degrees in 30 minutes.
When comparing the heat results, the CMH ran the lowest with an increase of 9 degrees. This was followed up by the LED with a 10-degree increase. The HPS had a 16-degree increase while the dual CMH closely followed with a 20-degree increase.
Our PAR Output test measured the light intensity coming off of the grow lights. These PAR charts were measured during our testing. All lights were hung 36 inches or 3ft. above the ground. Between the CMH, the HPS, the LED, and the dual CMH, These are the results:
The 630w Dual CMH grow light emits the most intensity out of the 4 charts. A strong 900-700 PAR rating in the middle and an average of 500 PAR in the outer area. If you were growing 4 plants in a 4×4, each plant will receive a near consistent light coverage throughout its growth cycle under the DUAL CMH.
There is a significant difference in PAR ratings between the dual 630w CMH and the single 315w CMH. Coverage is still consistent overall, but a single bulb impacts intensity. In certain applications, we recommend using the 315w for smaller grow tents or only utilize it for the vegetative cycle.
The traditional high-pressure sodium 600W bulb shows off the 2nd most intense light in the test. Providing 600-700 PAR rating in the middle of the canopy and tapering off to 500-300 in the outer area.
These numbers actually show a testament to grow tents. If you look at these numbers vs the numbers from another test we did, you’ll see that the grow tents and reflective walls impact lighting in a major way.
(Just so we are completely transparent on this PAR chart, the lights used were tested in a grow tent where the grow light may have slightly swayed back and forth during testing. We tried our very best to maintain steadiness but keep this in mind when looking at the numbers.
We had our test with the 600W HPS in a fully built grow tent at 36” from the ground and the intensity is more consistent all around the grow tent. Keep this in mind the next time you choose to grow in a dedicated room. Reflective walls make all the difference between a mediocre harvest vs monster yields)
Wavelength Comparisons & Final Notes
In conclusion, we would rank the dual CMH as the most intense light in the test. Couple that intensity with a quality spectrum, you can’t go wrong with this type of setup in any home grow.
Looking at these wavelength graphs, you’ll notice a few impressive features that the CMH emit vs the HPS grow bulbs. One major difference is how complete the CMH spectrum is. Not only that, but the addition of stronger UV production in the CMH bulb is great for resin growth.
The HPS grow bulbs are very focused in the near red spectrums which is great if you’re only utilizing HPS bulbs for flowering. But the CMH 3100k, with a wide array of available spectrum’s it emits, is a full cycle bulb lots of other HPS bulbs can’t touch.
3K Bulbs are full phase bulbs- We recommend it from clones to flowering.
4K is a broader spectrum bulb- They lean towards more veg-focused plants. These can be used to supplement for flowering but the 3k is more than adequate.
315W is equivalent to a 600W standard HID grow light when it comes to spread. However, a CMH light is more intense, provides a higher quality spectrum, and half the cost and heat!
CMH lights will cost more when purchasing but will save you in the long run.
CMH is the best lighting possible for in-home growing. They’re efficient, run cooler than HPS or Double Ended bulbs, and with all the benefits of the new and long-time growers alike can’t go wrong.
Editor’s Note: This article was originally published July 2017 and has been updated on 3/23/2018 for quality, accuracy, and comprehensiveness