Grow Light Intensity
Grow light intensity is a really important factor to consider and also really confusing. I’ll go a little into the details, but the basic point is CMH grow lights put out way more intense light than LED grow lights ever can.The intensity directly relates to canopy penetration.Here’s the idea, there’s physical law about light called the “Inverse Square Law”. It states that the intensity of light is inversely proportional to the square of the distance from the light source.Sure, reflectors and multiple light sources change things a bit, but it doesn’t change the fact that the light intensity drops steadily.
More canopy penetration generally translates into denser, bigger buds.CMH grow lights can penetrate 18 to 24 inches into the canopy when they are hanging three feet above. Where LED grow lights can only penetrate 6 inches deep, and must be suspended 6 inches above the canopy.It also means that since the LED light is so weak to start off with, it won’t penetrate into the canopy. Even if you hang it six inches above the canopy. And you’ll be adjusting the hanging height of the lights really often.But since CMH grow lights are so intense to start off with, the light will penetrate much deeper through the canopy. This means you’ll get a higher gram per watt with CMH grow lights over LED grow lights.And you probably won’t need to adjust the light height as often.The only case where LEDs are a better option here are low ceilings, and LEDs work great for under canopy lighting
. I believe if you’re working with ceilings less than 8 ft in height, it’s a good idea to use LEDs.
If you haven’t already thought about how long you’ll use your lights, you may want to consider it now.I’ve helped lots of growers over the years. Most of the time people keep their grow lights for two or three years before swapping them out. Warranties expire, new technology comes out, the grow lights themselves eventually don’t perform as well as they did when they were new.That said, you can replace the CMH grow bulb every six months to a year and it will perform like new. Assuming you’re cleaning your reflector
too!LEDs are supposed to last eight to nine years before their “usable life” is over. But often times a diode here or there will fail. And in that time the system itself will become outdated. Even with a long lifespan, LEDs light output will steadily fade over that time period. Nothing lasts forever.The math on a long term investment looks good on paper for LEDs, but it doesn’t reflect most real world scenarios.
Let’s talk about the size of your grow. Because of the lack of overall canopy penetration, you will need to keep your LED lights 6 to 18” above your canopy.This could be a good thing if your ceiling height is less than eight feet and you really need to be careful with your heat management.But, like I mentioned above, if you have a larger and taller space, using CMH technology is a better choice.An increased ceiling height allows for better heat management, better air-flow capability and more even light coverage for fuller and taller flower strains.Then there is technology like DimLux Half Force
, that turns the lights on and off, every three hours, in a checkerboard pattern throughout the grow room. This system works well because the lights send out so much light that they overlap. Even when every other light is turned off. Basically, there is enough light intensity for the plants to grow at near its maximum potential. Regardless if the light directly above them is only on half the day.LEDs cannot do this. They are so much close to the canopy, and the LED light output lacks intensity. LED grow lights are also unidirectional, so the light doesn’t spread out like a CMH grow light can. So all the LEDs must be on all on at the same time.