The first thing everyone searching for autoflowering cannabis growing with CFL bulbs should know is that you CAN grow autoflowers with CFL(compact fluorescent light). The end yield and plant size won’t be anywhere near what the HID(high intensity discharge) lamps can produce, but you will still be able to produce some fine auto flowers and do it all not spending hundreds of dollars on sophisticated light systems. Auto CFL growing is perfect for beginners or growers who have small growing space or heat problems as these CFL bulbs don’t produce much heat and can be put in close proximity of your cannabis leafs.

So what exactly are These CFL lights?

The compact fluorescent lamps are basically the same as the regular fluorescent light tubes but much smaller and compact. The way that this lamp works is similar to the regular fluorescent tube: The low pressure gas (typically argon) and a bit of mercury are sealed in a glass shell that has a coated layer of phosphor. When electricity is provided to the lamp it excites the mercury vapor that is in the glass shell. This Excited mercury then produces ultraviolet light that causes the inner coating (phosphor) of the bulb to fluoresce, producing the light that we can see. Typically the compact fluorescent lights are designed to fit into the regular household light fixtures and they are typically 5 times more economical than the incandescent bulbs. And that means a very cheap grow operation! Another bonus for using these CLF lights bulbs while growing autos is that they will last five times longer than the incandescent bulbs and at those bulb lifespans you will probably see many harvests before the bulb brakes.


Some people may confuse the wattage that is shown on the CFL bulb and think that the incandescent equivalent wattage is the real number to look at but you should really be looking at the actual compact fluorescent lamp wattage. The actual wattage that the CFL uses is the thing that you need to check and that is the real amount of watts that the bulb will use while producing light. The incandescent equivalent of the CFL is almost 5 times higher and that means if you buy a 20 Watt CFL with 80 Watt incandescent equivalent then the actual number of Watts that your bulb will use is 20. And that means more money to by some more autoflowering seeds or additional bulbs! Those 80 watts is only a number that shows what wattage incandescent bulb you can replace with your CFL and get the same amount of light and lumens.

So now we know how CFL wattage’s are measured but what are the best wattage bulbs to buy? There are various choices from 13W to 200W and even 250W CFL bulbs but which are the best? You can grow autoflwoers with all of those bulbs and if you choose the low wattage bulbs you will need many bulbs scattered around the plants but if you choose the 250W then that one bulb could be enough ! Basically the lower wattage bulbs( 13W to 25W) have too low light output and they are not as efficient as for example the 40W or 45W bulbs. From the other hand the bigger Wattage bulbs are too expensive and also have lower lumen output per watt(efficiency) so the most efficient bulbs are in the mid range from 30W to 50W and with these you will get the biggest bang for your buck!


The lumen count is the amount of light that the bulb can emit and more is obviously better. 1 lumen is the light that one candle can emit multiplied by one steradian. Usually CFL light bulbs have a lumen to watt ratio of somewhere between 50 and 80 and that is a good number compared to the incandescent bulb lumen to watt ratio of 10. And you need  around 2000 to 5000 lumens per square foot of growing autoflowering plants.  The lumens that are emitted by a CFL light diminishes very quickly (exponentially) and you need to get the bulb as close to the auto plant as possible. If your cannabis plant is very close (1 to 4 inches) to the bulb then it will receive the stated lumen ratio that is mentioned on the packaging, but if you move is 2 times farther it will receive 4 times less lumens (the start lumen count divided by 2 squared). This means that you need to have multiple CFL bulbs around your autoflowering plants at a very close proximity to maximize the growth and yield.

CFL Reflectors

CFL bulbs emit light in all directions and if you don’t have cannabis growing all around the bulb then those sides that are facing away from your autoflower plants are trowing away light! This can be partially fixed with coating all your grow room walls with reflective materials like Mylar that will reflect all the light back to the pants but that light will be less intense! The best action to take is to introduce a Light reflector that will reflect most of the light from the tree unused sides of the bulb to the one side where the plants are growing. With a proper reflector you can increase that bulbs intensity by almost 300 % and that amounts to more buds and bigger yields!

Color temperature

The color temperature is the temperature of an idealized physical body that absorbs all incident electromagnetic radiation (think of a black metal) when it’s heated to the specific temperature. like for example, if the temperature is 2700 K then the “black body” would glow at a warm yellowish white color (warm white) but if the temperature of the “black body” is more than 5000k then the light is “daylight”.

In nature the “daylight” or the 5000+  K light shines on wild ruderalis plants early and mid stages of growth but when the “warm white” 2700- K light start appearing as the sun’s light is scattered more and more by the atmosphere as the sun is not as high as it is in summer. Regular cannabis plant would start to flowering but autoflowering cannabis plants can grow and grow until they are trigger to start flowering automatically. This mean that the majority of the CFL bulbs must be “daylight” when your plant is growing and producing leaves and stems( for the first 2 to 4 weeks), but when it start flowering you can switch some of your bulbs the “warm white” spectrum but it is not necessary as you are growing autoflower seeds that are not effected by light cycle and will flower under almost any light. The best way to grow with CFL bulbs is to supply equal amount of 2700K and 5000K to 6400K lights and maybe even some bulbs that have 4000K equivalent light because then your plants will get all color spectrum lights and will be able to produce more buds!

One more CFL advantage is that much of the light emitted by these lights is usable to cannabis plants in the photosynthesis and if you would compare a 200 Watt HPS lamp and an equivalent wattage CFL bulb setup then you could see that the HPS produces 25 % more lumens but the  Photosynthetically Active Radiation or PAR index of the HPS bulb is much lower and basically those two set ups would be equally efficient in producing buds but the CFL bulbs run at much more cooler temperatures and you can space them out to get more light on more leafs and buds!


CFL bulbs are perfect for autoflowering cannabis growers who have a heat problem because they emit very little heat and you can even touch the bulb with your hands and not get burned. Your cannabis plant leafs can be very close to the CFL bulb and not get any heat burns and receive the maximum lumens without any losses. Basically the closer the light is to the plant the better –  the best distance between the autoflowering cannabis plant and the CFL bulb is around 1 to 4 inches (2.5 to 10 cm)!


  1. for flight news on

    F*ckin? awesome things here. I?m very satisfied to peer your article. Thanks so much and i’m looking ahead to contact you. Will you kindly drop me a e-mail?

  2. greenthumbeire32 on

    The above statement is quite true, however for about 150-200 euro, you could get a 400-600 watt HPS (high pressure sodium) bulb, reflector and ballast. this will use more electrcity. but the difference in buds will be noticable if done correctly. could be the difference between a dry yield of 10g’s to 40g’s.

  3. Great site. New to indoor micro growing. Have Super Box from Super Closet. The company that I bought my Feliz 200w “Blue” says to keep the lights 18-24 inches from light. Isthat too far away? Anyone out there have an answer or recommendation? Growing two Short Riders in 2gal Super Pots (fabric). Happy Frog/Perlite soil. Thanks

    • It could be true, but it depends on your grow room environment, you need to check the temperature around the 20 inch mark and if it is less than 29 C then it is OK, but I think that you can get them closer! I think that 10 to 15 inches would be acceptable but you should check the temperature around that height and if it is around 30C then get some fans to blow on the plants canopy and ventilate the heat away!

  4. Instead of using many of the smaller cfl’s which are about 40w,alot of people use lots of these with equal amounts of bulbs with correct spectrums.This uses more electric & a strain on the power sockets,cost etc.Why not use a giant dual spectrum cfl bulb,from 125w upwards,this fine for clones,single plants,but a 300w bulb is great for a single big plant or 3+ plants.You can get dual reflector shades for them,meaning 2 x 300w cfl bulbs in one shade,air cooled too.These bulbs are cheap to run,no heat problems.Warning though..after fitting your bulb,wipe all finger pribts off bulb as many find out leaving greasy prints on a bulb will heat up & bulb go bang! Try them!

    • Hi lee,
      Have you checked the lumen per watt efficiency ratings on those big bulbs?
      Usually they are less efficient than smaller CFL bulbs and that means you are wasting electricity and that is the real reason people use a bunch of smaller bulbs!

    • Will huskisson on

      Hello iam looking to do my second grow with around 4-6 autos but want to use CFL lights to help keep my cost down not 100% sure on what the best watt to use would be or how many lights units to use, any advice would great thanks.

  5. ZombiiCatfish420 on

    Ok so I’ve got only 5 CLF bulbs that are between 13 and 18 watts with a total out put of 80 watts total in a closet with enough space to hold about 9 plants in it but it’s painted a sand color instead of a flat white and I can’t afford Mylar right now, how many autoflowering plants will I be able to grow at once??? this was all I could afford for now and I’m just getting stated, will it effect my yield??? I’m trying to get as big of yield as a I can so I can sell my buds to be able to afford upgrading my lighting system to LED grow lights. I’m starting out with ordering 4 autoflower seeds, some advice would be greatly appreciated please and thank you. (I really need this to work so I can afford to buy a car, yes I’m super broke and ghetto)

    • Hi,
      I can’t give any advice on selling cannabis as it is illegal, but as for the growing process, Those 80W of CFL’s will not be bright enough to grow 9 plants. I would suggest planting only those 4 seeds and see how it goes. But be ready to add some more lights when they start to flower!

  6. Nick King on

    if I get T5 for 3/4 of my sides whats will be best for top of plants. total 6to9 plants

    • Whats your budget?

      I like to mix fluorescent lights with LED’s because I usually grow in small spaces and can’t get rid of all the heat from HPS lights.

      You can get some high power LED fixtures or you can also get another T5 grow light fixture with more bulbs and place it at the top of your plants.

      But it all depends on your budget, size of the grow room and your own preferences.

  7. Hey,
    I’m going to grow 4 autos in about a squaremeter area. I can use mylar on the walls and i can afford reflectors. I’m thinking about putting 2 x 300w dual spectrum cfls over them. Is that too much power for 4 autoflowering plants and what do you suggest about cfls (about watts, spectrums etc)

    • That should be plenty of light for 4 plants but 300W bulbs will create a lot of heat so you will also need a great ventilation system. If you want to install two CFL’s then buy one daylight and one warm white bulb to maximize the light spectrum in your grow room.

  8. Arnold420 on

    I got x1 100w cfl and x1 300w dual spectrum cfl is that enough to make 4 good or even 5 autoflowers if i buy reflection plastic? I got a low budget som i cantact yet buy another 300w dual spectrum i’m still not sure about this som Hope you Guys could help me out:)
    Thinking about buying auto blueberry

  9. I have been useing 2 250watt CFLs for both Veg & bloom in a 4x4x6,5ft grow room for about 6 years now.
    My last harvest was from 2 White Widow auto flower and I pulled off 10oz of each plant dry!
    I used to use a 1000Watt MH & Hps for growing the same plants and not much difference in yield.
    And CFLs produce a lot less heat. I have over 35 years growing weed So I have to laugh at all these Pro growers who claim the MH, Hps or Led is the way to go. I dished out maybe $400 for my whole setup and every 70 days I can bring in over 3k in income.

  10. Hi I have 4 auto seeds and I have 2×200 watt cfl dual spectrum My grow is it correct? Enough for light flowers? Thanks..

    • Yes, that set-up with 400W CFL’s should yield you a nice harvest and if you are a first time grower then that will be a great place to start your growing career.

  11. Hey peeps I’m growing again after a year away, I was new to it then but I got a bit stressed last time because I had issues with the hps and hight temps so ive just bought my self a 250w blue and 250w red, I have a tent which is 90x90x180cm and wondered if 4 auto’s with a 250w in that space would be ok? thanks

    • I have a maxsisun mf 1000 and 1 65 watt and 2 13 watt cfl 2700k cfl for your me auto in a 2 by 2 grow space is that efficient????

  12. Dark Street tent 90x90x180cm, max 4 plants probably autos, with 250w cfl blue & red. Will it be sufficient ?

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