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LED or CMH–Which is Best

Why MaryJane Farmer Thinks LED Grow Lights Are the Best Choice.

We recently got a comment from a reader asking why we don’t feature CMH (Ceramic Metal Halide) Grow Lights on our site.  We have talked about why we think LED Grow Lights are the best choice for our readers, and how LED Grow Lights are different from the older HID lights.  So now it’s time to talk about why MaryJane recommends the best LED Grow Lights over any CMH lights.  There are multiple reasons, but it boils down to this: Mary Jane Farmer (Betty Crocker for Weed) thinks LED Grow Lights are the best choice for indoor marijuana growers, who usually are not growing for massive industrial cannabis companies.  In this post, MaryJane explains why she thinks LED Grow Lights beat CMH Grow Lights on almost every metric.

Ceramic Metal Halide (CMH) lamps have until recently been the king of indoor grows but now there are full-spectrum Light Emitting Diode (LED) lamps. Many of the companies selling Grow Lights push CMH lamps hard.  Maybe that’s the inertia associated with having a big inventory of unsold lamps on hand or possibly associated with serving clients who installed CMH lamps a long time ago and now need to replace the bulbs and ballasts and air conditioning units that go along with CMH. The arguments against LED grow lamps, mostly on price, are falling almost monthly and are beginning to sound rather self-serving – in 2016 LEDs were only for wealthy early adopters but today in late 2021 there isn’t a huge difference in price. Thank you, China.  LED grow lamps are now the complete winners over CMH lamps.

What Is a (CMH) lamp?

Like the High-Pressure Sodium (HPS) and Metal Halide (MH) lamps that they are intended to replace, CMH lamps use a tube-like bulb with gas inside the tube.  When electricity is shoved through the gas, it creates an arc, very much the same as electric welding works.  (“Arc welding”.  Get it?) . Basically, that is the way all these types of lights work–by burning the gas inside the tube.  That’s why the bulbs have to be replaced.  The gas eventually gets burned up.  The temperature of the CMH lamp gets as high as 1200 kelvins.  Not Kelvin the Frog. Kelvin the Temperature which is approximately 1700 degrees Fahrenheit. HOT. And hot is basically the big problem MaryJane sees with CMH lamps. In addition to replacing bulbs.  And in addition to replacing the electric ballast, which is the gizmo hanging off the end of the light that controls the electricity.

Is Ceramic Metal Halide the same as Ceramic Discharge Metal Halides (CDM) or Light Emitting Ceramics (LEC)?

Basically, these are abbreviations that all mean essentially the same thing. A ceramic piece delivers a charge to a gas inside the lighting tube, much like a fluorescent bulb uses wires to deliver a charge to a contained gas.

What is Good About CMH Lamps?

CMH grow lamps such as the TopoLite kit cost slightly less than LED lamps. If you’re new to growing this could be a major factor, but only if you are planning to make a very very large indoor farms with lots of lights.  Otherwise, buying a couple of LED lights is not more costly than CMH lights for your grow operation.

CMH also delivers more canopy penetration, measured in ‘photosynthetic photon flux (PPF). A good CMH lamp system like the Sun System LEC 315 has a PPF of 1.95, which means that the light will get into the lower levels of the plant, allowing for better flowering from the top to the bottom.

The light spectrum of CMH lights has long been the reason that they were king of the hill in indoor growing. The sun has a color rendering index (CRI) of 100, while a good CMH lamp comes close to that at 92 CRI.

CMH lights also produce a wider physical reach so you needed fewer lights per square foot of growing space than an LED system.

What’s the Problem with a CMH Lamp?

HOT.  The first thing you need to consider when going CMH is an effective air conditioning system because they produce an awful lot of heat. Remember Kelvin?  When you turn on a CMH light, you are basically starting a fire inside a ceramic aluminum tube.  Though LED Grow Lights still need a cooling system, you won’t need anything as expensive as under a CMH light.  And most LED Grow Lights come with a heat sink or a fan that is sufficient to cool the lamp for growing purposes.

With the cooling system (usually air conditioning or huge fans and exhaust systems) you will find that you consume a lot more energy using a CMH light. (Unless maybe you live in Siberia or Greenland.) As of today, the total operating costs of a CMH light including initial investment is more or less comparable to the cost of buying a good quality LED Grow Light.

What About Maintaining a CMH Lamp?

At different stages through the growing cycle of your ladies, you will probably need to change the CMH lamp bulbs for a different spectrum. During the vegetative phase, you will need a blue-biased lamp bulb to help the plants grow to the size you want. When it comes to flowering you will need a lamp with a redder spectrum to encourage the plants to produce the buds you want. This extra investment and added messing around is no fun for the newer grower with all the other things you need to learn to do (such as feeding, light/dark cycles, and heat maintenance).

How do LED Lamps Compare to CMH Lamps in Operation?

Comparing an LED grow lamp such as a Mars-Hydro FC-E Series or a Samsung Quantum Board Dimmable Full Spectrum Grow Lamp, there is less manual work to do than with CMH lights. Most of the best LED Grow Lights have a switch that allows you to adjust light/dark cycles and red/blue spectrum according to the different growth phases of your plants.  (Blue for bigger plants, red for robust buds.)  You are saving time for enjoying your crop, instead of changing light bulbs.

Warning. Stupid Joke Ahead.  Q: How many farmers does it take to change a light bulb? A: None, if you are MaryJane Farmer because you have LED.

The best LED grow light companies usually give you a warranty in the range of 100,000 hours. You may have gone through five CMH bulbs and two CMH in that time. With their lower power use and fewer parts to replace, LED grow lights soon start saving you money in capital and operational outlay.

They are also far cooler, and with their slightly lower PPF this means you can and should hang them closer to the plants than a CMH system. For someone looking to grow in a smaller space such as a loft or cupboard, this may make a lot of sense.

LED grow lights come as single units. On a CMH system, you will need the lamps and the ballasts, and there are more things to think about when it comes to a CMH setup.  MaryJane prefers a system with as few parameters to worry about as possible and this is another reason to consider LED.

As with everything in life, you get what you pay for. A better LED system may involve a greater initial outlay but nothing as bad as back in 2016 when comparable quality LED lighting to a CMH system could have cost you several hundred dollars more per unit. Today with operational costs you will get your money back in a very short time, while a few years back this could have meant four years or more.

The PPF and CRI ratings on LED Grow Lights are often a little lower than CMH. Growers get around this sometimes by ‘scrogging’ so shorter plants with higher yields are grown, getting around the PPF issue. This might mean a wider floor area and more lights. If you are willing to spend good money on a decent LED light then you will find a better CRI rating.

A good LED grow light system is going to allow you to spend less time worrying about lighting variables and more on the other complexities of your indoor grow. A good LED may still cost a little more than a CMH grow light system but operational costs soon claw back the investment.

What Does China Have to Do with LED Grow Lights?

Yes, MaryJane knows that CMH grow lights sometimes cost less and can reach more plants per unit. They are marginally better in light spectrum and canopy penetration but she doesn’t have to change out the bulbs according to the growing phase. With the operating costs included, CMH lights have been losing ground to the LED newcomers and are now rarely recommended.  Chinese companies are now producing cheaper but still high-quality full-spectrum LED grow lights. And some of the Chinese companies, such as Mars Hydro, have US service centers for any problems that might occur.

As LED systems have improved, they are steadily killing off CMH just like CMH lighting killed traditional metal halide and HPS a few years back.  MaryJane sez that a good LED grow light system is now a much better option than CMH and is now the king for indoor lighting.

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