Jul 12, 2019

LED vs. CMH Grow Light Technology

Light Emitting Diodes or Ceramic Metal Halides?

Have you found yourself digging through Google pages full of LED hula hoops and burning man posts to find out more about LED lighting technology? Want to know how they stack up to LECs? Suffering from a case of FOMO when it comes to your yields? Learn from decades of lessons learned the hard way.

Ceramic Metal Halide

Ceramic metal halide lamp lightbulbs

Ceramic metal halides (CMH), also known as ceramic discharge metal halides (CDM), are also known as light-emitting ceramics (LECs). There are a lot of names for the same bulb and technology. CMH fixtures pull low watts and cover large areas, making them an energy-efficient choice when comparing your lighting choices.

CMH tends to be a long-time favorite with growers. They came on the market to replace high-pressure sodium lights and regular metal halides. CMH fixtures offer a bulb with a longer lifespan than their predecessors and are designed with a higher color rendering index (CRI) that more closely mimics the spectrum of the sun. The Sun System LEC 315 has a 92 CRI rating. For reference, the sun has a CRI of 100, and an HPS bulb has a CRI of 25.

LEC 315 fixtures are offered in two different spectrum heavy options—a 3,100-kelvin red heavy lamp, and a 4200-kelvin blue heavy lamp. You want to use the blue spectrum light during your vegetative state, and switch out your bulbs to the red spectrum in the flowering phase to get the most out of your plants. LECs, whether it be 315w or a 630w, have a lifespan of 20,000 hours, and their ballasts are rated at 50,000 hours.

LED Grow Lights

Young tomato plant under hydroponic LED grow light

Light-emitting diodes (LEDs) work a lot differently than CMH fixtures. Instead of one long bulb, as the LEC uses, LEDs are made up of hundreds of little lights called diodes. Each of those diodes is a set specific spectrum of light. LEDs come in panels that combine hundreds of different diodes spectrums with others to create a large panel of full-spectrum light.

Some LEDs come in strips and are great for growing things in rows, like for growing produce in a greenhouse. For growers looking for more even light distribution and larger coverage, there are many different-sized panels to choose from. There are also many different LEDs on the market that combine their diodes differently to provide different spectrum heavy panels. Creating the perfect balance of spectrum for your precious budding babies is important in giving them the ideal environment in which to grow.

One of the differentiating factors about LEDs is that they are dimmable and micro-adjustable. This means you can dim your lights from a higher blue to a more red spectrum with the turn of a dial. It allows you to cater to your plants and their stage of growth without having to change out bulbs or move your plants into a finishing room. This is such a cool breakthrough in grow light technology! This is very handy when your plants may be experiencing a large amount of heat and you need to bring it down a notch, literally. For its consistent, superior lighting technology, our personal favorite LED on the market right now is NextLight.

Which Grow Light Do I Need?

There are benefits to both kinds of lighting. For example, CMH fixtures provide a lot of light energy and cover a very large area. The dimming capabilities of LEDs are something not offered by any other light. So, which do you need? That depends on the size of your grow, how long you will be growing (will you be growing for 1, 2, 5+ years), and your budget? All questions you need to answer.

It is not worth the cash to use LEDs to propagate your plants. Seedlings or clones require such little light energy so we recommend going with a cheaper lighting option if that is all that is in your grow space at one given time. Using a T5 fluorescent fixture, bumped up with Hortilux PowerVeg T5 bulbs, is a cost-efficient way to get your plants vigorously underway. This way you aren’t wasting the limited life of your expensive LEDs or CMH bulbs.

Again, don’t waste your money on using one of these bad boys for propagation. Your cheap little T5s will work beautifully. One CMH fixture can cover a 4×4 or 5×5 growing space during the veg stage and a 3×3 in the flowering phase. The Sun System LEC 315 has a high 1.95 PPF (photosynthetic photon flux) per second light source. This means it is effective at penetrating the canopy of your plants to offer light to the entire length of vertically growing plants.

The comparable Next Light version of the LED would be the NextLight Mini. It only pulls 150 watts but covers a 3×3 foot veg footprint or a 2×2 flowering footprint. LEDs are known for not having the same light intensity as CMH fixtures, but we have found that the Next Light Mini does a comparable job and is rated at 1.73 PPF per watt. The NextLight offers a five-year manufacturer warranty on their fixtures, so at least you have peace of mind should anything happen to your investment.

Get Lit

Hydroponic growing iceberg lettuce indoor

Hanging your lights was made so much easier when pro grips were invented. All CMH and LED fixtures should come with V-hooks attached to them that will make hanging them a piece of cake. Set yourself up with some Sun Grip Light Hangers. They create a pulley system that attaches to your V-hooks with carabiners. Cinch those babies up and enjoy the ease of movement you have with your pulleys when you need to adjust the height of your lamps.

The light hangers are really useful when you consider that the Sun System LEC 315 weighs in at just over 20 pounds and the NextLight Mini weighs 12 pounds. Not something you are wanting to have to lift and move up and down like an old-school chain hanging system when adjusting your height by just a couple of inches. Plus, with the pulley system, you can adjust heights when the lights are on without having to wait until the lights are off and they’ve cooled down enough to touch.

Do Your Grow Lights Hang Too Low?

CMH fixtures put off quite a bit less heat than their counterparts, but still produce heat nonetheless and you still need to get rid of that heat so you don’t overheat your grow. You are going to want to place them higher than you would with LED. The recommended height is 24 inches from the canopy of your plants to avoid bleaching or burning your leaf tips.

CMH fixtures are not air-cooled and will emit most of their heat directly down towards the plant canopy. To help distribute the heat, you have to HVAC Like a Pro.  Proper ventilation and airflow are one of the most important parts of having a successful grow op. Oscillating fans are a huge help in moving the warmer air around that tends to sit at the canopy throughout the room. Read our blog to learn more about a strategic setup to ping pong warmer air to then let it be pulled up and out through your exhaust system.

LEDs can be placed much closer to your canopy. The recommended distance is 12-18 inches from your plants. They emit a majority of their heat out the backside of the bulbs, in what we call a ‘heat sink’. This heat sink hits the aluminum reflector of the fixture, which helps to disperse the heat over a larger area. This aluminum panel works to get a longer life out of your LED bulbs. The heat coming out of the back of the bulb doesn’t just sit there and slowly burn them out, one by one.

Protect Your Eyes In Your Grow Room

Seriously though, have you spent time in your grow and walked out of your room seeing spots? You’ve got to protect those peepers. When growing indoors, you are trying to recreate the power of the sun with your grow lights. Spending too much time working underneath them can cause some serious damage to your eyes.

Wearing your favorite pair of Ray-Bans might ward off a few of those UV rays but you should consider investing in a pair of growing glasses, like the Method Sevens. They work with any type of lighting that you choose to install in your grow and allow you to see your plants with clarity without causing damage to your retinas. Cataracts aren’t fun—put on the shades.

So, What Is My Grow Light ROI?

The return on investment is going to be higher on CMHs if you see yourself growing for less than five years. To be real, the initial costs of setting up an LED system make it impossible for some growers. Especially because there are a lot of other parts that go into a grow (i.e. air conditioning, nutrients, etc). You can’t blow your cash load all on your lighting. If you are in it for the long term, investing in LEDs will save you money over a longer amount of time in both bulb replacements and energy costs.

If you know that you have a fear of commitment, don’t worry. Using CMH lights in your grow has been seen by our growers to provide a higher yield in vertical growing plants due to their higher PPF and canopy penetration. It allows you to get the most out of the less expensive option of the two types of lighting; even if you are going to be replacing bulbs about once a year.

Let’s Break it Down

Both CMH and LED fixtures are great for growing a high-quality product but they do have their differences.


  • Initial costs are lower
  • Bulb lifespan is 20,000 hours
  • One-year warranty on the lamp
  • Ballast has a 50,000-hour lifespan
  • Recommended to change bulbs for veg and flower stages
  • Higher PPF and canopy penetration
  • Better standalone lights
  • Offers full spectrum lighting in one bulb


  • Initial costs are steep
  • Bulb lifespan is 50,000 hours
  • Manufacturer guarantee of 5 years, Unit has 100,000-hour lifespan
  • Numerous narrow bands of the spectrum create a full spectrum
  • Dimmable
  • Better supplemental lights

The More You Know the Better You Grow

LED technology is continuing to develop—making them more cost-effective and appealing to a novice grower. In our experience, those that have tried them out like them but prefer the results of CMH technology, especially considering the start-up cost of an LED setup. Don’t feel like you need to keep up with the latest trends though if your budget doesn’t allow it. Ceramic Metal Halides provide a great product and provide a great lighting option for your grow.

Want to learn more? Stop into one of our seven store locations and talk with our knowledgeable staff or visit our blog page for other ways to improve your grow!