With more powerful types of grow lights (like HPS or LEDs) you can light-burn your plants even in cool temperatures, like a sunburn. But with CFLs it’s almost incredibly difficult to give too much light so your main job is to get as many bulbs as you can as close to the plants as possible (without burning your plants from heat). Note: Don’t get CFLs confused with old-fashioned incandescent light bulbs! CFLs that are in the 40-42 watt range are great for growing marijuana, and also make great seedling, clone and/or supplemental lighting.
Follow these principles with CFLs to get great yields every time: 1.) Start with about 150W worth of CFLs, which is enough light for one small plant. Because the penetration of CFLs is poor, many smaller CFLs is more effective than a few big CFLs because they can be spread in an array around the plant. For example, 4 x 40W CFLs (at 160 watts total) will usually get bigger yields than a cannabis plant grown under 1 x 200W CFL, even though the smaller bulbs use less electricity in total. For tiny plants in a small setup like a space bucket you want 20-30W CFLs. If you plan to grow your plant up to a foot tall, you may want to use 40W CFLs and bigger since the smaller ones won’t have enough penetration to reach the bottom of your plant. 40W-sized CFLs are a great combination of power and penetration when it comes to growing cannabis with CFLs. There are bulbs with different CFL color spectrums and it’s generally recommended to get “daylight” (6500k) CFLs for the cannabis vegetative and “soft white” (2700k) CFLs for the flowering stage. Each color spectrum has a small impact on how the plant grows (ex: 6500k encourages slightly more squat growth).
But the truth is that total power , or total wattage of your CFLs, is much more important than spectrum with CFL grow lights! If you do want to get all of one color spectrum, get all “soft white” (2700k) CFLs, or whatever is cheap and can give you the most watts for your money. We will go into much greater detail about CFL color spectrum below, but the main takeaway is that watts is far more important than spectrum! 4.) Total Yields to Expect from CFLs (0.25g/watt) This will help you estimate how much yields to expect from your CFL grow, but you need to remember to take this with a grain of salt. A very general rule of thumb is to expect about 0.25g/watt of CFL light if you use plant training and don’t run into major plant problems. This is counting CFL true watts, not any type of “equivalent” watts. Some CFL growers definitely get bigger yields than that with CFLs, up to about 0.5g/watt for the pros, but 0.25g/watt is what you should expect as an upper limit for a first-time cannabis grower. So if you use 150W of CFLs (as recommended to start with each plant below) you can expect about 37.5 grams, or a little over 1 oz per plant. If you add more CFLs for each plant, you will increase your yields somewhat proportionately to how many watts worth of CFLs you add. The size and shape of your plant is going to have the biggest effect on both your cannabis yields and how many CFLs you’ll need. That’s why no “formula” is going to be accurate all the time; marijuana plant training makes such a big difference on your final yields and its impossible to know what a grower’s skills will be. That means any formula is just a rough estimate, but if you follow the steps in this CFL growing tutorial you’ll produce great results every time so you get the cannabis CFL yields you expect, or even more! Examples of Cannabis CFL Setups – How many CFLs Should I Get For Each Cannabis Plant? Here are example setups as far as how many and what kind of CFLs to get for each marijuana plant! Getting many bulbs tends to work well, but getting all those light sockets and arranging all the lights in an easily adjustable way can be a pain. Larger bulb setups let you use fewer bulbs in total to deal with, and have slightly increased penetration, but as they continue to get bigger they become more unwieldy and start generating a lot of heat. Each CFL Setup Example is For One Cannabis Plant – Expect a Little Over 1oz of Bud. A grower can expect a little over 1oz/plant with each of these CFL Setups, as long as they take great care of their plants, and train them to grow short and wide with many colas as outlined above in the step-by-step instructions above in this Growing Cannabis with CFLs Tutorial. B.) Medium Size CFL Bulb Setup 6500k colored bulbs (Sometimes called Cool White, Bright White, Daylight) Best suited to Vegetative Stage. By using the 6500k (sometimes “65k”) colored bulbs during the vegetative stage, you’ll be giving your plants more blue light, which can help a plant grow more short and bushy. However, you can still use bending and training to make your plant grow however short and bushy you want, no matter how it grows! 2700k colored bulbs (Soft White, Warm White) Best suited to Flowering Stage. The soft white 2700k colored bulbs have more reds/yellows that help your plant “get in the mood” for making buds. Mix Different Color Bulbs Together Best suited to Any Stage of Life. “Will a 5500k or 5000k photography CFL bulbs work for growing weed?
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 marijuana?” Any CFL will work for growing marijuana. Again, it’s much more important to get a high wattage than the right color spectrum. I’ve used 5500k photography CFL bulbs in the past and they worked well. As far as spectrum is concerned, blue (6500k) encourages shorter vegetative growth, red/yellow (2700K) encourages longer/taller vegetative growth and flowering/bud development. However, I’ve found they can all be used successfully in all stages of growing. What has a greater effect on your results is how much light (wattage) in total. For example, I’d rather have 150W of 5500k bulbs than 100W of 2700k bulbs for flowering. The increased light intensity will help your yields more than getting the exact right color spectrum. The increased wattage will give you more return on yields than getting the proper spectrum, so choose the cheapest CFLs you can get that will give you the most wattage!
This is what you use to get light to your bulbs from the wall.