Answering Your Top Questions on Ceramic Metal Halide Lights

One of the first questions every indoor grower must ask is, “What type of lights will I use?” This is becoming even more difficult to answer with the growing variety of indoor grow light options. Once you decide on a type of grow light, you have to choose which specific model works best for you and your operation. 

To help, GrowersHouse continually compiles guides to answer the top questions about lights that professional and beginner growers might have. While LED lights might be all the rage, ceramic metal halide (CMH) grow lights are an industry standard that can be highly worth their upfront cost.

Let’s explore everything growers need to know about CMH grow lights and answer the top CMH FAQ to help you decide if they’re the light for you.

Basics of Ceramic Metal Halide Grow Lights

First let’s learn a few basics about ceramic metal halide lights. Lighting is essential for optimal photosynthesis to occur, so the type of light you choose — its efficiency and power — will ultimately determine how well your plants will grow and how healthy they will be.

CMH fixtures are also commonly known as LECs (light emitting ceramic). They’ve been a premium lighting choice among home growers and professionals for quite some time. Keep these CMH facts in mind: 

  • Ceramic metal halides are a part of the high intensity discharge (HID) grow light category, along with other well-known light types, HPS (High Pressure Sodium) and MH (Metal Halide).
  • CMH light fixtures come with three main parts: a ballast, a hood or reflector, and a bulb. A ballast is essentially the heart of the fixture, responsible for controlling and delivering the proper current and voltage.
  • Ceramic metal halide bulbs give off UV-B rays, which may improve trichome production during the flowering phase.


Here are some of the most frequently asked questions and answers on ceramic metal halides:

What’s the difference between CMH and MH lights?

CMH grow lights use an arc tube made of ceramic rather than a quartz arc tube used by MH lights. The ceramic bulb delivers a more natural color, produces more lumens per watt, and lasts longer. The more natural light of CMH bulbs helps growers see the natural color of their plants. This means nutrient or health issues that show themselves with the discoloration of leaves, stems, or stalks can be caught more easily. In comparison, HPS lights tend to have a yellow hue, while many LED fixtures mix red and blue LEDs to produce a purple hue that distorts how your plants actually appear.

The base of the lamps also differs. CMH lams have a two-pronged G12 base. Most MH lamps have a mogul (screw-in) base like that of a traditional tungsten-filament bulb.

CMH lamps also require a different ballast than MH bulbs.

How many kelvins (K) are good, and for what benefits?

The color temperature of light is measured by degrees of Kelvin, commonly just written as kelvins or K. Kelvins typically range from 1,000 to 10,000 and varied degrees benefit plants during different growth stages. For the most part, lower kelvins are most associated with flowering, while higher kelvins are associated with the vegetative phase. Some kelvin levels can limit the use of the bulbs for shorter periods.

Compare the unique benefits of 3000K vs. 10000K bulbs for one of the best-selling CMH fixtures, Growers Choice Horticultural Lighting 315W.


3000K 10000K
Slight increase in UV light promotes resin production Strong UV peaks encourage resin production
A taller peak in far-red stimulates metabolic activity during flowering Can be used for 25+ flower cycles before replacement
Slightly higher PAR promotes better flower density For use only in the last 7-14 days of flowering
Increased intensity in red Durable quartz glass arc tube ensures long life


What's the footprint of a 315W? 630W?

Depending on the model, a 315W ceramic metal halide grow light tends to have a footprint of 3’ x 3’ to 4’ x 4’ when hung 2 feet above the canopy. A 630W ceramic metal halide grow light typically has a footprint of 5’ x 5’ to 6’ x 6’.

Are there 500W and 1000W CMH grow lights?

Like most grow light fixtures, ceramic metal halides come in a variety of wattages. Including 500W and 1000W.

What do ceramic metal halide reviews say?

Once converting to CMH light fixtures, it’s hard to deny the benefits they can provide to your crops. Overall, ceramic metal halide reviews say the advantages of using CMH fixtures outweigh the upfront cost, especially when it comes to efficiency. CMH bulbs are 20% more efficient than other MH versions and provide a higher yield per watt.

Can I convert MH fixtures to CMH?

Yes, conversion kits allow growers to easily change their metal halide fixtures into ceramic metal halide fixtures. One of the most popular conversion kits is a 315W made by Prism Lighting Science.

What are the pros and cons of using ceramic metal halide lights?

Of course, every type of grow light has its own pros and cons. If you’re looking for a simple comparison, based on your preference or needs, reference the list of advantages and disadvantages below -

Pros Cons
Produces less heat than MH or HPS - Ideal for small rooms with issues controlling temperature. UV-B rays can be harmful - While UV-B rays are to thank for higher resin and trichome production, it can be harmful to humans. Use proper safety equipment, such as UV protectant glasses when in the indoor growing space.
Color stability - CMH bulbs retain their wide color spectrum, while other spectrums, such as those from LEDs, can lose effectiveness without being detected. Higher setup costs - As we’ve mentioned, in the HID light category, CMH setups cost significantly more than MH and HPS setups.
Optimal CRI - While it’s hard for indoor lighting to mimic the energy and light of the sun, CMH bulbs come the closest. They boast the best color rendering index, or CRI, of 80-96.  Still produces high heat - Even though CMH fixtures produce less heat than MH or HPS, they produce more heat than LEDs. You’ll need to ensure you have proper ventilation and optimal airflow.


How long do CMH bulbs last? 

Ceramic metal halide bulbs are beloved by growers for their above-average longevity, especially in comparison with MH or HPS bulbs. In general, CMH light bulbs last around 20,000 to 24,000 hours (around three years), and maintain 80% of their original intensity after 20,000 hours.

Final Word on CMH Grow Light Fixtures

Now that you know more about ceramic metal halide lights, you can see how their benefits often outweigh their higher purchase cost over MH and HPs lights. CMH reviews rave about such advantages as optimal growth, health, and plant quality. As top manufacturers improve their products, processes and supply chains, the price of ceramic metal halide grow lights continues to become more cost-effective. If you can afford the higher upfront cost compared with MH or HPS, we recommend checking out the latest selection of CMH ballasts, bulbs, and fixture kits.