by Nebula Haze
What is a CMH grow light? (also known as a LEC grow lights)
CMH grow lights (also known as LECs) are great grow lights for cannabis, but they really “shine” (sorry I know) when it comes to producing an excessive amount of trichomes and increasing terpene production.
CMH/LEC grow lights typically produce more trichomes than other grow lights including LEDs… if you use the right bulb
Using LEC/CMH bulbs in the 4100k or 4200k spectrum will dramatically increase the number of trichomes produced in the flowering stage compared to other types of grow lights including LEDs. These bulbs work with any 315 CMH or LEC grow light ballast. Kick it up one more notch by using a 10,000k bulb for the last 1-2 weeks.
If you’re looking for the best cannabis yields or potency, I recommend going with an LED grow light. But if you’re most concerned with increasing trichome production and smells (and have a relatively cool place to grow; LECs get hot!), LECs may be the best grow light for you.
Sparkle city on this LEC-grown bud
Which LEC/CMH Grow Light Should You Get?
Here are examples of some of the most common and popular LEC/CMH grow lights by different manufacturers. I personally recommend the version by Sun System as it’s produced amazing results with the Philips bulb. In a side-by-side grow journal with an HLG Quantum Board LED, the Sun System LEC produced more trichomes and higher terpene levels even though the clones were otherwise grown in identical conditions (same nutrients, grow space, grow medium, etc.).
The UV rays from LECs cause the plant to produce more trichomes and terpenes as a stress response
- Sun System 315 LEC <– Recommended
- Optimal distance from plants: 18-24 inches (45-60cm)
- Comes with Philips 4200k bulb: excellent in the vegetative stage, and one of the best bulbs for cannabis trichome production
- Use a 10,000k bulb for the last 1-2 weeks to increase trichome production*
- Grower’s Choice 315W CMH
- Optimal distance from plants: 2.5-3 feet (76-91 cm)
- Comes with an unspecified 3KR Red Enhanced bulb – good for yields but not the best for trichomes
- Use a 10,000k bulb for the last 1-2 weeks to increase trichome production*
- Eye Hortilux 315W CMH
- Optimal distance from plants: 3 feet (91 cm)
- Doesn’t come with a bulb, either 4100k Eye Hortilux or 4200k Philips bulb recommended (here’s a cheaper off-brand version with the proper spectrum; it’s well-rated but I haven’t tested it myself)
- Use a 10,000k bulb for the last 1-2 weeks to increase trichome production*
- Vivosun 315 CMH
- Optimal distance from plants: 24 inches (60 cm)
- Comes with an unspecified 3100k bulb – good for yields but not the best for trichomes
- Use a 10,000k bulb for the last 1-2 weeks to increase trichome production*
*a 10,000k bulb will reduce yields if used throughout the flowering stage and should only be used for the last 1-2 weeks before harvest. However, these powerful bulbs have the ability to really crank up the trichomes when used correctly!
Soon you’ll be harvesting buds like this Pacific Punch grown under a Sun System 315 LEC
Can an LEC/CMH grow light be used from seed to harvest?
Yes! Cannabis plants thrive under LECs in both the vegetative and flowering stage all the way to harvest. Here’s a guide with information on how to get set up and use an LEC grow light.
These plants were grown from seed to weed under the Sun System 315 LEC grow light
Bonus: Pictures of plants grown under LECs that were submitted by our readers
LEC grown cannabis bud pic by the talented grower Jamie Arellano
Anonymous submissions
Happy plant under LECs
Submit your LEC or CMH grow light pictures for a chance to be featured here!