Does Light Matter - The Best Lights For Growing Cannabis

in #grow
3 months ago

Hell yeah, the light you use does matter. In fact, light will be one of the main factors in how much cannabis your plants produce and ultimately how much bud you will get to trim, cure and smoke.

Photo from CannabisNow

In this article we will cover the best lighting for growing dank buds as most growers aim to get 0.5g up to 1g per watt of light (so a 1000 watt grow light can yield up to 1kg (or two pounds) with the correct genetics, medium, nutrients and technique) and alot of hobbysts set ups use this metric to determine how much bud they might yield.

The first thing we need to understand before realizing this is not the best metric is to understand that not at light produces the same "light".

Let's start with sunlight at sea level. There is currently, and most likely never will be a commercial way to replicate the entire spectrum of wavelengths and intensity the sun naturally provides us with every single day. The suns light at sea level is about 93 lumens per watt.

Compact Fluorescent's, on the other hand, are mand made tubes of glass with a gas and some mercury inside and do some weird stuff with photons and electrons that excite the molecules and produce light through tiny explosions. only 17 lumens per watt. oh and some nasty radiation, wonderful right?

LED's seem to be not only the most effective and efficient lights at not only replicating sunlight but providing a whopping 130 - 200 Lumens per watt making them even "brighter" than the sun! Be sure to put your shades on when they on as they most certainly can fry your retina after long exposure. Unlike CFLs, LEDs are optimized to produce certain light spectrums. This works really well because cannabis needs certain light spectrums at different times throughout its life cycle.

If you’re into old-school technology, you can try an HID lighting system to grow your cannabis. This artificial light works on the same basic principles of growing weed just like stoners did back in the day before LEDs became popular. HPS dual-spectrum lamps use MH mode for veg and HPS for flowering and provide between 60 - 100 Lumens per watt, but these lights will run the meter, and they tend to be on the expensive side.

Image from Comsol

Sunlight makes for happy and healthy plants.

Photo from CannabisCulture

The best light for growing cannabis is the sunlight. Anyone that tells you otherwise is kidding themselves. Sunlight produces an average of 93 lumens per watt at sea level. It also produces the widest wavelength of light possible, which is incredibly difficult to replicate commercially.

Sunlight has its restrictions though, as in most parts of the world planning and planting is done during spring and harvesting during autumn making for a once a year harvest. Most outdoor growers use the winter to trim, cure and prepare products for market while prepping genetics and clones indoor for the next season.

Various techniques such as creating a greenhouse or vegging indoors can create for a perpetual harvesting cycle or grow in colder climates that do not have full sun during summer.

Tips for sunlight

  • Make sure your plant is getting at least 8 hours of direct sunlight and more than 12 hours of total light during the vegging stage for maximum results.

  • A simple plastic or light shade netted greenhouse with fans / heaters can help maintain temperatures in extreme climates.

  • Make sure you plan for watering as the sun can dry out the medium much faster than indoor light.

Compact Fluorescents might seem good at first...

Photo by GrowWeedEasy

However, you just won't get what you looking for. If you’re on a budget, you can start out with Compact Fluorescent ( CFLs ); however, the plant will not grow to be much taller than 2 or 3 feet and might stretch.

If you only use CFLs throughout the whole cycle expect to get upset, cos you’ll be pissed off with the amount of buds you will end up with. CFLs just do not have the right light intensity and spectrum as seen in this study. Though some growers manage to get decent yields using CFLs.. here is the TLDR:

Tips for CFL Grow Lights

  • You will want to build a homemade light that has at least 4 to 6 100W CFLs installed and wired together on a wooden board to grow one or two plants.

  • If you start your veg cycle with CFLs, do not switch the light to LEDs during the flowering stage. This will stress the plant out, and in some cases, it may not flower at all. You can however put small plants outside after they have vegged under CFLs.

  • Keep your plants under CFLs for both the veg and flower cycle, and adjust the timer from an 18/6 to 12/12 lighting schedule when the veg cycle ends.

  • Keep the plants as close the CFLs as possible to avoid stretching.

Why are LEDs Better for Growing Weed?

Photo by plantozoid

Modern technology for LEDs are now available with switchable-technology from veg to flower, and some even utilize UV technology to get the most cannabinoids out of your cannabis plant during the last couple weeks of its life. Most LED grow lights on the market are more efficient than HID lights, have a longer lifespan, consume less energy, and are very durable.

Tips for LED Grow Lights

  • It’s a good idea to get a set of adjustable rope hangers because you will need to keep raising the LED light as the plant grows.

  • Because LEDs run cool, you can keep your LED light really close to the plant without burning the leaves; however, a distance of 12 to 24-inches is recommended by most growers.

  • If you’re using LED lights inside of a reflective grow tent, you will need an exhaust fan and another small clamp fan blowing on your cannabis plants because LED light will produce a small amount of heat out of its built-in exhaust fans. If you don’t have fresh air circulation and keep the humidity levels down, condensation can form on the tent’s interior walls.

Which lights do you use to grow your plants and why?

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Great tips plug, thanks for the share....judging by your results there is no doubt you are a pro!

Just wanted to give my 5 cents regarding the LED lighting and growlights in general.

I've noticed you were comparing them based on their lumen value...while it was sort of relevant with regards to the more conventional bulbs like HPS or Florescent, as they are more wildly used and therefore standardized, calculating their "plant relevant output" (Photosyntheticly active radiation - PAR) can have a certain formula.

But as lumens are actually a human metric, it is based on the sensitivity of the human light and how it processed photons and as the human eye is way more sensitive to green light, therefore a light containing more green wavelengths will have a higher Lumel/Lux value then light with lower "amounts" of green light.

But plants prefer other wavelengths - the PAR range of the spectrum - there are many theories on the subject but that PAR range usually contains mainly RED and BLUE light, and mostly emits the Green.

Plants absorb virtually no Green light (at least not trough photosynthesis) , and are most sensitive to Red light - while Infra Red is like a little sun for them (we barely see infra red)...

so lumen reading can me some what relevant calculating plant light needs but only from sources that have some other data available...

Regarding Led light it will be virtually there are so many manufacturers, diod types, reflectors, encasing...etc...and the technology is developing by the day...

Usually those Led Grow Lights are manufactured emitting the green light all together...thats why they look puprle or in those cases the Lumen reading will be even more confusing...

As measuring the Lumen output of a "purple" led light will give you a lower reading of its white equivalent (white has green inside) - while the "plant radiation" output is actually higher...
That can be very problematic...

So the only viable way to measure or compare those light is by their PAR and PPF readings, that can be converted to total daily Light integral (DLI) and even that is not 100% proof as PPF reading also can vary based on the ratios of the RED and the BLUE light ...

Unfortunately the only way to measure PAR or PPF is by a quantum meter or other expensive equipment....thats why the Grow Light market is such an unregulated market, and you dont really know what you paying the manufacturer can write whatever he wants and there is no cheap way to know if he is right...

Apologize for this manuscript :)


PAR counts the number of photons from 380nm to 780nm (extended spectrum).
One PAR are 6,022 * 10¹⁷ photons and one PPF is one PAR/second.

The plant also uses green light by Carotinoide.


You are absolutely right about the green light, i actually was mistaken on this one, i was sure it was only utilized by the plants on the biological levels (PBAR )and not through photosynthesis , but i do stand corrected, seems that green light is important after all!

I guess that was actually quite apparent, as i had a few chances to send a "Full spectrum" led lights trough a hollow sphere and comparing on various growth cycles for some work testing purposes, and you could clearly see that the presence of some white colored diodes among the reds and the blues would increase the yields of the final product and will show a more ""natural"growth pattern.

You also right about the PAR and the PPF definitions, we should probably also add PPFD - being the total amount of those photosynthetic active photons that actually land on the canopy of the plants, and DLI - being the total daily light integral - basically all the active photons that landing on your canopy in your total lighting period - 12h, 16h etc...

IMO even more important is to know the efficacy of the actual lamp, baically how much of the PPF this light can produce using X amount of electricity.

It worth mentioning that if you measure most of the fixtures from about 2-3 years ago, at best their efficacy would be at about 1-1.2 PPF to 1 watt of electricity, so basically a light that is drawing 100 watt from the wall, will generate about 100-120 PPF, but more modern lights go up to 2.5-2.9PPF per 1 Watt.

Yet again another misconception that watt matter in growlights...higher quality, more technologically advanced light will generate more Photons while using less energy then less advanced lights....

Nevertheless, Lumens are still a bit irrelevant for our matter.

To quote the same source as your reference :

"The fundamental problem with using LUX or foot candle meters when measuring the light intensity of horticulture lighting systems is the underrepresentation of blue (400 – 500 nm) and red (600 – 700 nm) light in the visible spectrum. Humans may not be efficient at perceiving light in these regions, but plants are highly efficient at using red and blue light to drive photosynthesis. This is why lumens, LUX, and foot candles should never be used as metrics for horticulture lighting. "


Hi hope im not to late to get some info ..I want to grow some mango kush indoor so I am looking at lighting and not sure which one to take and if any of them are any good at all the others are crazy expensive so would you mind taking a look at these 2 and tell me what you think?
600W LED Grow Light For Indoor Plants Growing Lamp 225 LEDs Full Spectrum Lights
or this one
![]800W Hydro LED Grow Lights Lamp Full Spectrum IR Veg Bloom ECO Indoor Plant()


I guess a 45w would be out of the question


Great info thanks

I prefer 3000K white COB LEDs with a CRI of 90 and white reflector.

Most LED stripes are only available with a CRI of 80 (lack of deep red).
Most manufactures add therefore extra red LEDs (first picture).

Good info.

Unless something has changed, efficiency of CFLs tops out at around the 40w range. It's much more efficient to run CFLs in the 20'ish watts, and multiples of them. You'll get deeper penetration and a higher yield per watt. :D

That being said, LEDs are what I'm slowly transitioning to after 15+ years of HID. :)

At the moment, in my grow box, I'm using 4 Feit Electric 100w replacement (uses 17.5w) LED's with the domes removed. 2 soft white - 2700k and 2 daylight - 5000k. They say the bulbs brightness is 1600 lumens each. I plan to add some of their grow LED's to my setup.

Awesome info mate, thanks for that, seems like the LEDs are the most practical but as always nature knows best. Bong on bro.