If you are into growing indoors or are seasoned growers, you must have known CMH grow lights - one of the modern light technologies that stir the interest of a number of hydroponic growers recently.
But how much do you know about it? And which CMH products are the top quality and best suit your needs? I'll explore all about these in this guide.
If you to see our recommended CMH lights, see below. We do a whole review of each product at the end of the article as well.
What are Ceramic Metal Halide grow lights?
Actually, Ceramic Metal Halide (or CMH) grow lights are not new; they were first developed in the late 60s, and it's not until recently that they are acknowledged and used commonly as grow lights.
Ceramic Metal Halide (CMH) or Light Emitting Ceramic (LEC) are two different terms, but both refer to the same technology. So basically, we can use these two interchangeably. In this article, I'll mostly use CMH.
A CMH grow light is like a Metal Halide (MH) bulb, but while a MH bulb uses a standard quartz arc tube, CMH is built with a ceramic arc tube. This is similar to the material used for HPS grow lights. So that's can be said that CMH is a mix between MH and HPS.
Since it uses ceramic arc material, CMH is less degradative than both MH and HPS with up to 20,000 hours of lifespan. CMHs can operate at a higher pressure and emit stronger light output than HIDs as well.
Advantages of CMH grow lights
This is the first winning point of CMH over HIDs light. CMH bulbs have much a wider and more consistent spectrum.
So besides having enough light intensity, plants also love to have sufficient light colors/quality to have their best growth potential.
More UV rays
Under high pressure, CMH bulbs can produce powerful light output that contains Ultraviolets (UV) like the sun.
These UVs include UV-A, UV-B, UV-C, especially UV-B which is really helpful for plant growth, overall all 3 types of UV are harmful to human eyes.
So you should not look at the bulbs directly for a long period. And most good CMH brands use a protective glass filter to block harmful UV types.
Since they are built with ceramic arc tubes, CMH grow lights have a great lifespan of up to 20,000 hours. But reality shows that they can last longer than that. This is more than double the average lasting hours of HID (HPS and MH) bulbs.
The initial cost of getting a CMH bulb/system might be more than other lights. But with better energy output and coupling with a longer lifespan, it can save you much in the long run.
The Downsides of CMH Grow Lights
Cannot compete with HPS for the flowering phase
Nothing can replace HPS when growing plants in their flowering phase. This is because HPS vibrate more reddish & yellowish wavelengths at high intensity. These wavelengths are vital to boost plants to flower, produce fruits, and grow vigorously.
Even though CMH bulbs do not manufacture much heat like the standard HID lights, they still give out lots of heat. So it's not really efficient for smaller growers with small space. So if you have a high wattage bulb running in a closed system, some ventilation methods must be done.
CMH grow lights are not for those with a tight budget. Though CMHs are much cheaper than a quality LED lamp, you should be ready to spend at least $500 at the start. But what you'll have is a quality and durable grow lamp that can produce high yield and last you for years.
CMH Grow Light Coverage
CMH lamps are recommended for universal positioning. This means they can be positioned vertically or horizontally above the canopy. The position won't cause damage to the bulb.
The position won't affect the light distribution, and every plant will have a consistent absorption rate. The grow light must be hanged minimum 3ft above the canopy to avoid any hot spots. This also provides an efficient and even light distribution.
The light distribution is so intense that a bulb with 315W can have a coverage area up to 4ft x 4ft. This is larger than what higher wattages MH and HPS bulbs provide.
An increase in the watts leads to a bigger coverage area. The higher watts contribute to greater heat produced. Make sure you hang the grow lights at least higher than 3ft above the plants to cancel out the effects of the heat.
The table below shows the recommended coverage of each CMH bulb and the distance from plants you should keep.
|CMH Bulbs - Recommended Coverage and Distance From Plants|
|315W||3ft x 3ft - 4 ft x 4ft||2 ft|
|630W||5 ft x 5 ft - 6 ft x 6 ft||3 ft|
Spectrums of a CMH bulb
Despite depending on the type of bulb temperature you get, CMH grow lights all have very wide spectrum wavelengths. They produce high red, yellow and green color temperatures. Each color has its own role in promoting the plants through the different lifecycle stages.
- Red: This color is responsible for the flowering and fruiting of plants.
- Yellow: This colored light spectrum improves the effects of photosynthesis.
- Green: This is used to elicit specific plant responses such as stomatal control, phototropism, photomorphogenic growth and, environmental signaling.
CMH lamps don’t have high outputs of the blue spectrum like other 2700K bulbs or blue LED lights on the market, which are great for veg stages. However, they do have sufficient blueish light colors to grow in the veg stages.
Commonly, you'll run into two versions of CMH bulbs on the market.
- 3,100K (full-spectrum) bulb has more colors in yellow, red and green, which can be used for full growth (from cloning to flowering)
- 4,200K (broader spectrum) bulb contains wide wavelengths but has more blueish wavelengths; So is more suitable to grow seedling and veg plants; They can be used to grow flowering phases, but the 3100K is more efficient.
Spectral Distribution of a 3100K CMH Bulb
Spectral Distribution of a 4200K CMH Bulb
Comparisons between CMHs and other grow lights
There are heated debates about which grow light technologies are better. Here we list all the differences between CMHs and other popular grow lights, including MHs, HPs, LEDs so that you can easy to understand.
|Comparisons Between CMHs and Other Grow Lights|
|Types of grow||All phases||Suitable for veg||Suitable for flowering||All phases|
As you have seen from the table, CMHs beat MHs in every way, except the initial cost. But what you get from the investment is a more well-balanced bulb with broader spectrum, longer durability, and higher light intensity.
In comparison with HPS, in a lot of tests done by growers, CMHs even have stronger PAR output than HPs at the same wattage, which proves more light efficiency. CMHs also have lower heat, longer spectrum, and more durability. The only situation, HPs are more efficient is when you grow plants during their flowering phases. But the heat issue from HPs do irritate lots of indoor growers.
So if you need only one bulb during the whole growth, I would recommend CMH grow lights, they are a better all around grow light over HPS and MHs - produces well-balanced broader spectrums, high intensity and can last longer.
LEDs do have their stand compared with CMHs with a longer lifespan, lower heat, full spectrum. However, the large startup cost and the powerful light output and wavelengths make CMHs still favored by either small and seasoned growers. LEDs can last to 5 years while a CMH lamp should be replaced after 4 heavy grows, or every 2-3 years.
Best CMH Systems
For the best results and security, I would recommend you buy a CMH kit. This way you don't have to worry if the ballast works with the CMH bulb or not. And a kit also comes with an already set-up reflector and glass that protects harmful light for human and keep the UVs that are helpful for plants.
Dimension: 24.1 x 19.7 x 11.7 inches
Weight: 20.6 pounds
Lifespan: 20,000 hours
Warranty: 1 year
Dimension: 20 x 12.5 x 12 inches
Weight: 12.05 pounds
Bulb: 315W Phillips Master color 3100K Lamp
Warranty: 1 year for the lamp; 2 years for the fixture
Also Good Budget Pick
Dimension: 24.1 x 21.4 x 11.8 inches
Weight: 20.5 pounds
Ballast: Built-in inside of the housing
Warranty: 3 years
Included packages: daisy chain socket, 120V - 240V adapters, power cord.
Best CMH Bulbs
Power: 315W, Option for 630W
Temperature: 3100K. Option for 4200K
Par: 570 μmol/s
Lifespan: 15,000 hours
Ballast: Recommended for low-frequency ballast
Warranty: 1 year
No doubt CMHs are efficient and durable grow lights that will bring great yield for your hydroponic gardens. So I hope this guide has shed some lights for you about this great technology and help you pick the suitable CMH systems or bulbs of your choice.
To sum up, if you are looking for a quality CMH system, I would recommend the Sun System LEC for its popularity, great build and proven light efficiency.
For single CMH bulb, get the Philips Master product. Though these bulbs are more expensive than other bulbs on the market, you get a longer durable bulb and more consistent light output that your plants love.