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Growing Weed With CFLs - What Growers Need to Know
by Nebula Haze
In the past, we’ve covered how to grow train your plants to grow short and how you can maximize your space when choosing an auto-flowering or photoperiod strain, I’d like to share some tips for growing with the cheapest marijuana grow lights that fit in extremely small spaces... CFLs!
What are CFLs?
CFL stands for "compact fluorescent light" and even though these lights can be found at any hardware or grocery store, they actually give off a really great light spectrum for growing marijuana.
Never get CFLs confused with old-fashioned incandescent light bulbs...
Benefits of growing with CFLs
CFLs are easy to find in grocery and home improvement stores
Suited to very small grow spaces
CFLs are a great option if you...
Must grow in a very small space (computer case, cupboard, or tiny closet)
Plan to grow 1-2 plants
Want to harvest a few ounces of buds
Are willing to check on your plants at least once every few days (you will need to adjust the CFL grow lights relatively often since they’re kept very close to plants)
CFLs are not well suited for growers who want this...
Lots of plants
Pounds of buds per plant
Large grow tent
Refuse to learn [how to train plants]
Can’t tend plants regularly
How Many CFLs Do You Need To Grow Marijuana?
There are lots of formulas that growers can use to determine how many CFLs they will need.
For example, some growers recommend that you go by the amount of lumens (light) produced, or by the total wattage of your lights.
However, I think a simpler approach is much more effective, and will result in better yields for you.
Simply follow these principles with CFLs to get great yields every time:
All parts of the plant should be within 8-10” of a CFL bulb (CFLs should be kept 2” away from the tops of your plants
Any “shadowy” areas need another bulb
More bulbs = better results (You want to surround your plant with as many bulbs as possible because the penetration of CFLs is poor; in other words, more small CFLs is more effective than a few big CFLs)
Real-life Example: 7 x 26W CFLs (at 182 watts total) that are spread in an array around the plant will be more effective for growth than 1 x 200W CFL, even though they use less total electricity.
More lumens = better results (you can’t really give your plant too much light when growing with CFLs, more is better)
In the flowering stage, make sure that buds get direct access to intense light & keep CFLs as close to buds as possible without burning them (this will dramatically increase yields with CFLs)
The size and shape of your plant is going to have the biggest effect on how many CFLs you’ll need, and that’s why no “formula” is going to be accurate all the time. Any formula is just a rough estimate.
What if I’m still not sure how many CFLs to get?
You can use this formula to get started with planning your grow space, though I recommend using the guidelines above once your plant has actually started growing.
4,000+ lumens/sq foot (more is even better) - lumens is the measure of light as perceived by the human eye, and this number will be listed on the CFL bulb packaging
Example of Estimating Number of CFLs Needed For Your Grow Space:
Multiple width x length of your grow space to determine the sq feet.
Let’s say your grow space is 2’ x 2’ = 4 sq feet
Multiple the sq feet of your space by 4,000 lumens to determine the total lumens needed for this space.
So 4 sq feet x 4,000 lumens/sq feet = 16,000 total lumens for that space
Divide this number by the lumens produced by each bulb
If you’re getting 42W CFLs which are rated at 2,650 lumens apiece, that would be 16,000/2,650 = ~6
This number is the minimum number of CFLs needed for your space
That means in this case you’d start with 6 (or more) 42W CFLs
Remember, this formula is just an estimate, and you will get the best results if you also follow the guidelines listed above.
Tip for maximizing the light to your plants: Use the power of reflection to minimize light loss. Cover your walls with reflective mylar or paint them with flat white paint. Utilize reflectors to aim more light where you want.
What Color CFLs Should I Get? (CFLs and Light Spectrum)
When you’re buying CFLs, they come in different “colors.” Some are more orange/yellow, some are almost blue, and others almost look like daylight.
The truth is that all CFLs will work for growing, but some are better than others....
6500k colored bulbs (Cool White or Bright White)
Best suited to Vegetative Stage
By using the 6500k colored bulbs during the vegetative stage, you’ll be giving your plants more blue light, which helps plants grow short and bushy.
Will a 5500k photography CFL bulbs work for growing? I know you're supposed to get 6500k colored bulbs in the vegetative stage, and 2700k colored bulbs for flowering...
I have a 150w 5500k photography bulb which looks identical to other bulbs rated 5500k specifically sold as "grow bulbs" so could this be used for growing?
Any CFL will work for growing marijuana. I've used 5500k photography CFL bulbs in the past and they work great.
As far as spectrum is concerned, blue (6500k) encourages shorter vegetative growth, red/yellow (2700K) encourages longer/taller vegetative growth and flowering.
The 5500k bulbs are in between. However, they can all be used successfully in all stages of growing.
How much light (wattage) will have a much greater affect on your results, and more light/wattage is better with CFLs. It's almost impossible to give plants too much light with CFLs.
For example, I'd rather have 2 x 150W 5500k bulbs than 2 x 100W 2700k bulbs for flowering. The increased light intensity will help your plants more than getting the exact right color spectrum.
The increased wattage will give you more return on yields than getting the proper spectrum.
I'm still not sure which grow lights to get... You may be interested in this discussion on the pros and cons of CFLs vs HPS grow lights for a small space: http://growweedeasy.com/cfls-vs-hps-grow-lights
I want to see a real CFL grow in action! Show me a CFL dresser microgrow with lots of pictures: http://growweedeasy.com/entire-microgrow-pictures-week-by-week
I'm definitely choosing CFLs... if you know you’re ready to get started growing with CFLs, click here to view my step-by-step tutorial on growing weed with CFLs in coco: http://growweedeasy.com/easiest-grow-method-cfl-coco-coir
I'm thinking about choosing HPS grow lights instead... Help me pick out the right lights and teach me how to set them up: http://growweedeasy.com/hps-grow-lights-setup
These CFLs are proven for growing marijuana. They also make great supplemental lighting.
Reflect your light for max efficiency
Use reflectors (or make your own like WasabiMayo does below!)
To all you growers on a budget: It's possible!
Check out WasabiMayo's amazing (and budget) CFL microgrow in pIctures...
View full album with a write-up by WasabiMayo right here: