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Compact fluorescent (CFL) grow lights

What Are CFLs and Why Use Them

CFL lights are the “Tom Cruise” of grow lights: ubiquitous, efficient and perfect for short spaces (up to 4’). Another Tom Cruise-like attribute is that they are considered the ideal candidate to take up the “Mission Impossible” of growing in confined spaces.

In the old days growing marijuana under fluorescent (CFL) grow lights was pretty useless as they had low output for a large size. However, the new CFL (compact fluorescent lights) grow lights that between them cover the full visible light spectrum have made them a viable alternative.

But what exactly are CFLs?

As you probably know by surfing the internet and this website, there are many different light types. HID (HPS, MH), LED etc., are competing for a place in your grow room and every one of them has an ace up its sleeve. CFL stands for (Compact Fluorescent Light). Chances are that you have already come across a forum debate that outlines the pros and cons of each lighting type. We too are going to attempt a comparison between the different lighting options, but for now, let’s just focus exclusively on the CFLs.

marijuana-grow-lights-comparison

marijuana-grow-lights-cfl

CFL Pros and Cons

Pros

  • They can be found anywhere: CFLs are obtainable in every hardware and grocery store (WalMart, Sears etc.). There are also huge offers to be found on Amazon and Alibaba;
  • Cheap as chips;
  • Ideal solution for your makeshift PC tower grow box, cupboards and similarly confined spaces;
  • They run at considerably cooler temperatures than traditional light fixtures. That makes them considerably safer due to lower fire hazard;
  • Their chiller temperatures also mean that they do not need too much external cooling to stay at normal levels.

Cons

  • Not particularly strong. HID light fixtures are considerably more powerful, so consider these if you are after bigger grows;
  • Unsuitable for larger grows.

Like everything else in marijuana growing, it all comes down to your personal needs and preferences. There is no one stopping you from installing an HPS lamp in a 2’x2’x4’ closet (good luck with that!), but this is the consensus among growers from all over the world.

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People who should go for CFLs

  • People who want to grow a plant or two for personal use;
  • People who have turned their obsolete PC tower or their grandma’s commode into a grow room;
  • People who want to try growing a plant but don’t want to spend much.

On the other hand, if you are looking for massive yields and a more automated growing setup, steer clear of CFLs. The rule of thumb here is that when you need something more than 250W of power, you are better off with some other type of light. We have a whole section for you to choose what suits your needs best!

A little bit of science

There are a lot of variables to consider when choosing grow lights. Grow light science can confuse you a little bit at first, but after a while, you should know what you are looking for. If you want to learn more about the scientific jargon, it is strongly suggested you do so by visiting our relevant page. If you believe that you are fairly knowledgeable about the facts below, you can skip this part and go straight to the shopping list. The rest of you, take a deep breath and follow us to the exciting world of lighting science.

Wattage and the Kelvin Scale

Your objective when buying CFLs should be to purchase the wattage (W) that is the highest possible for your grow area. Usually, more wattage means more power, which in turn means more light, and thus, more food for your plants. If you want to determine the suitability of the lights, you will want to also check the lumens (lm) to understand their output.

marijuana-grow-lights-kelvin-scale

Generally, each plant should be covered by around 10,000 lumens. So if a standard CFL bulb gives off 2,500 lumens, you’d need 4 or more of those, until you reach the desirable levels. CFLs come in 15, 26, 42, 65, 68, 85 and 105W versions, although larger models do exist. A 42W CFL lamp (the best you can use for marijuana growing) emits about 2700 lumens. Four 42W CFLs use 168W and emit 10,800 lumens. More powerful CFL lamps maintain a similar Watt/lumens ratio, so you get the picture. You can easily check the lumens of your light by using this handy calculator here. It is generally advised to keep using CFLs until you reach 250W of power. Anything more than that is overkill and you should probably consider switching to a more powerful light. Remember, CFLs are more suitable for small-scale operations.

But that’s not all; this is where the Kelvin scale comes to play. For those who skipped our lighting tutorial (shame!), this scale is used to measure the “color temperature” or “frequency” that is emitted by light bulbs. Marijuana plants love red and blue light, so you are basically looking for bulbs that are as close to that as possible. Interestingly enough, HPS lamps emit light that is mostly in the yellow spectrum (meaning that most of it goes to waste). And this is where the CFLs shine (pun intended): although they are much weaker than HPS lights, the amount of usable light they emit is higher than theirs. As we have repeatedly written in this website, different growth stages require different light spectrums. Check the package for the Kelvin spectrum indicated and choose accordingly.

marijuana-grow-lights-cfl-package

CFLs come in 2700K, 3000K, 4100K, 5100K, and 6500K models. Bulbs on the lower side of the Kelvin scale, like the 2700K, are more suitable for the later stages of plant growth, while 6500K ones are better for vegging. If you use the in-between spectrums, then you get a nice and balanced result by modifying the rest of your bulbs accordingly.
Every indoor growing light ever is designed to mimic the sunlight. In nature, the sun produces different rays in the spring and summer (blue, vegging) and different rays in the autumn (red, flowering). The sun also produces green, and orange rays, but cannabis plants do not use them.

  • Warm white bulbs offer the red-yellow spectrum of light, which is ideal for the flowering stage.
  • Cool white bulbs produce more blue spectrum light and are good for the vegetative state.

Vegetative Stage – 5000K / 6500K

marijuana-grow-lights-vegging

Bulbs that are more blue are called “Cool white” or “Daylight” colored and are listed with a Kelvin of 5000K / 6500K. These “high kelvin” bulbs are optimal for vegetative growth when your plants naturally need more sunlight.

Flowering Stage – 2700K

marijuana-grow-lights-cfl-flowering

Bulbs with a more yellow/red tint are listed as “soft white” colored with a Kelvin of 2700K. These “low kelvin” bulbs are optimal for the flowering stage when your plant thinks that winter is coming.

Some Great CFL Models

Here are some of our favorite CFL models and their specs. Although there is no reason to be overly picky with your bulbs when growing with CFLs, these fixtures are ideal to get you started.

Agrobrite T5 4′ 4-Tube Fixture – EnviroGro

agrobite-t5-cfl-grow-light

This model comes two sizes: 2’ (23” x 13.5” x 3”) and 4’ (48.5” x 15.5” x 4.2”) and five patterns (2, 4, 6, 8, 12 tubes), offering you a wide range of customization.

Specs

  • High efficiency specular aluminum for maximum reflectivity;
  • Can be hanged in three ways: overhead, vertical or horizontal;
  • 10′ grounded power cord;
  • Includes 4 fluorescent 6400K, T5 tubes, that make this fixture ideal for the flowering stage of your plants;
  • 5-year Ballast Warranty, 1 Year on material and workmanship.

Apollo Horticulture 5-Pack of 2′ T5 Bulbs – 2700k and 6400k

apollo-horticultire-t5-bulbs

These tubes come in both 2700K (bloom) and 6400K models (growth), so you can pick whichever suits your needs, according to your plants’ stage of development.

Specs

  • Package Includes 5x T5 Light Bulbs of 24W Each;
  • Size: 23.5” x 4.6” x 2.6”
  • Color Temperature – 2700 K;
  • Lumen – 2,200lm;
  • Dimensions: Length – 22.12″ / Diameter – .62″.

Dayspot 26W, 6400K Bulb – Hydrofarm

dayspot-hydrofarm-cfl-grow-light

This CFL spiral bulb provides you with all the light you need, while at the same time reducing energy costs.

Specs

  • 26W – 6400K bulb, equivalent to a 130W incandescent lamp;
  • Lumens: 1600lm;
  • Lifetime: 10.000 hours;
  • Size: 6 x 2.5 x 2.5”.

Sun Blaster 26W, 2700K Bulb – Future Harvest

sunblaster-26W-cfl-grow-light

The SunBlaster 26W CFL light bulb was designed with growers in mind. They will fit in almost any light fixture and they their output is equivalent to that of a 100W incandescent light bulb. The 2700K spectrum, means that they are a perfect choice for the later stage of plant growth.

Specs

  • 26W – 2700K bulb, equivalent to a 100W incandescent lamp;
  • Lumens: 1700lm;
  • Lifetime: 10.000 hours;
  • Size: 2 x 1.2 x 0.3”.

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How to Use CFLs for Cannabis Growing

If you still believe that CFLs are what you need, then we are assuming that you have a limited space to work with. Therefore, the following tutorial will be focused on growing a single plant. In reality, this is a short tutorial on growing small with CFLs, but there are some useful lessons along the way. If you are completely new to growing, you are advised to carefully read our in-depth tutorials and visit our forums. This will solve 90% of your questions. Go on, we’ll be waiting.

The Basics

Back already? Assuming you have done your homework (or at least have grown -basically any- plant before), you know that houseplants need three things in order to survive, in this order: light, water, and nutrients. Marijuana plants go through three major stages of development that are universally acknowledged among cannabis growers: seeding, vegging, and flowering. All these transitional phases are determined by distinct patterns in the lighting cycle . In reality, there are many transitional periods that are also important, but these three should be your main focal point (at least for now). You can find more on marijuana grow phases here. Cannabis plants have no pre-determined sex. Therefore, you should make sure that the conditions you provide promote the development of female plants (the ones who provide you with smokable buds). More on that here.

Reflective Material

In order to make the maximum use of the light from your CFLs and reduce light leaks, you will need to cover your grow space with a reflective material. These will distribute the lighting more evenly across your plant, ensuring that no corner will be left in the dark. Even the best of grow lights can not penetrate the whole of the plant on its own, so some reflection is needed. Mainly, you’ll be looking at these options:

Foylon

how-to-build-diy-marijuana-grow-room-foylon

Pros: Durable, easy to maintain, 90-95% reflection

Mylar

how-to-build-diy-marijuana-grow-room-mylar

Pros: Popular, cheaper, 92-97% reflection (2mm version)

Matte white paint

how-to-build-diy-marijuana-grow-room-flat-white-paint

Pros: Cheap, can be found anywhere, 80% reflection

Panda plastic

how-to-build-diy-marijuana-grow-room-panda-plastic

Pros: Easy to clean, perfect short-term solution, 80% reflection

Orca Grow Films

how-to-build-diy-marijuana-grow-room-orca-grow

Pros: Mold resistant, easy to clean, expensive, 95% reflection

All of these options are readily available online or at home improvement stores. However, consider opting for the easy solution, which definitely a grow tent. It comes as pre-built setup and it will be already insulated and coated with reflective material. If you are impatient or not quite the handyman, check out the offers by Dealzer and Superlcoset. Grow tents are versatile, cheap (contrary to grow boxes) and they have been designed with growing in mind.

Supplies

Here is where things get interesting. Assuming you want to grow just one plant, you need at least 150W of CFL power. Although you can play around with the lighting, the optimal CFL arrangement would be 2x40W 5000K-6000K bulbs + 2x40W 2700K bulbs. You are welcome to experiment, but this is the foolproof approach!

Things to take into account

  • CFLs’ light penetration is poor, so, many smaller CFLs are more effective than a few big CFLs. Their light can be spread more easily (although you should cover your grow space with reflective material beforehand). 4 x 40W CFLs (160W) will get bigger yields than 1 x 200W CFL.
  • CFL bulbs under 40W are usually a waste of money. On the contrary, 40W+ CFLs are ideal for small scale growing (up to 250W).
  • At this scale, power is more important than Ideally, you’ll want to combine the two (and frankly, that is not too difficult to do). Getting more juice should be your top priority. However, learning one or two things about spectrum along the way can’t hurt, so we will expand upon this subject in the following parts.

Set Up

We started this article by stating that CFLs are the masters of growing in confined spaces. So, here is a list of grow rooms that CFL bulbs would thrive in.

  • Closet/Drawer

marijuana-grow-lights-cfl-grow-closet

Any old furniture will do if you have the patience and skill to turn it into an adequate grow room. Just be sure to properly insulate it. More info and how-to’s here.

  • PC Tower

marijuana-grow-lights-cfl-grow-tower

As the era of tower PCs is drawing to a close, it would be wise to find a new use for your old friend, with whom you spent hours of playing Quake 3. CFLs make great sources of light for a modified PC tower (more info on how to turn one into a grow room here).

  • Grow Tent

marijuana-grow-lights-cfl-grow-tents

Cheap, flexible and reliable, grow tents are by far the easiest solution if you are looking for a portable grow room. Check out our friends at Dealzer and SuperCloset for some really cool models! Just be sure to stay around the 2’x4’ range if you want to start small.

Seedling

marijuana-grow-lights-seedling-stage

  • Germinate your seeds and plant them, or just plant your clones;
  • At this stage, your plants should follow an 18/6 light cycle (that means 18 hours of light, followed by 6 hours of darkness). You probably do not want to do that yourself so get a timer for your CFLs;
  • Water your plants adequately (DON’T water them too much) and watch them reach the vegging stage.
  • Pro Tip: CFLs are awesome for the first weeks of life of a grow, especially seedlings. Regardless of their setup, many experienced growers prefer to use CFL in the first few weeks, so that they can reap the maximum rewards of CFLs.

Vegging

marijuana-grow-lights-vegging-stage

This is where things start to get serious. Your plant is basically just a baby at this point, so treat it like one! At this point, the plants need more daylight and therefore require “Cool white” or “Daylight” colored bulbs, that run at 5000-6500K.

  • Water it regularly (do not DROWN it);
  • Adjust your CFLs so they are within 4″ of plants (try not to burn them though). The rule is: if it’s too hot for your hand, it’s too hot for your plant!
  • Give nutrients (but not too many of them);
  • Train your plants to use as much space as possible. You can find extensive tutorials here;
  • Again: don’t overwater or overfeed your plants;
  • Don’t panic! – most plant problems are easy to fix.

Remember that plants are growing rapidly at this stage, so give them a bit of leeway so they don’t grow directly into the lamps. A good all-round solution is to train them. Not only do you reduce the risk of your plant crashing on your light bulbs, but you will also dramatically increase your yield. Training is a big part of a successful grow and it we have covered it extensively here at HTG. Here is a list of all the training articles we have presented on this website

Tips for efficient CFL vegging in a nutshell

  • Plant Training;
  • Adjust CFLs Regularly (daily if possible);
  • Keep CFLs Close – 4″ away from the top of your plants should do it (remember the hand/plant theorem!). Try to manage your space so that all parts of the plant are within 8-10” of a CFL bulb;
  • No part of your plant deserves to be in the shadows. Be sure that light is distributed equally;
  • Try not to move your plant around a lot;
  • More Watts=More Light=Better Results.

Flowering

marijuana-grow-lights-flowering-stage

When you switch your light schedule from 18/6 to 12/12, your plant will enter the flowering stage, responding to the fewer hours of daylight. This effectively tells your plant that it is time to reproduce because it’s going to die soon. At this point, you should run a check so you can make sure that absolutely no light enters your grow room during the dark period. Not even tiny blimps from electric devices. At this point your plants require bulbs with a more yellow/red tint. These are often called “soft white” and are colored with a Kelvin of 2700K. These “low kelvin” bulbs are best suited for the flowering stage, since your plant is getting ready to flower before winter comes.

Tips for efficient CFL flowering in a nutshell

  • Give your buds all the light you can – CFLs can work wonders at this point. Just keep them as close to your buds as possible (without burning them) and watch your plant yield like crazy;
  • Keep the temperature at adequate levels – If you read our tutorials, you probably know that temperature control is one of the cornerstones of proper growing. However, the flowering stage requires a bit more attention. Be a little more careful and, if possible, have a small fan blow gently on top of them.
  • Training is over – This is not the right time to train your plants. Generally, you should do that in the vegetative period.

When your plants’ buds fully develop, then it’s time for harvest. Lighting has nothing to do with harvesting, so for that, you can follow our in-depth guide! Just be patient and cure your buds properly!

Tip: If budget is not a problem for you, think about installing an MH lamp in the last week of budding. Many growers believe that it can improve the quality of the bud.

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CFL Compared to Other Light Types

CFL v HID Lights (HPS, MH)

marijuana-grow-lights-hid-vs-cfl

As we’ve seen above, CFLs are more suited to small growing rooms, so if you don’t have a lot of space, there is no question. CFLs will do the trick, as long as you readjust them every now and then. HIDs are more powerful and generally require less tinkering.

CFL v HID in a nutshell

  • In both cases, you will need some kind of ventilation for your grow room. It is worth mentioning, however, that fluorescent lights will make do with a simple 70CFM fan;
  • HIDs are more powerful but take up more space, so they are not as versatile as CFLs;
  • Although they are not as hot as HIDs, CFLs are not designed for gardening, meaning that they might cause unexpected problems;
  • Many growers use them in conjunction to improve their results.

CFL v LED Lights

marijuana-grow-lights-LED-vs-cfl

LEDs are the latest “it-thing” in growing technology. We have a whole section dedicated to the LEDs pros and cons here in HTG. Let’s see how they fare against CFL lights.

CFL v LED Lights in a Nutshell

  • LEDs are a newer piece of technology. As such, they are more efficient and they tend to get better yields for the same amount of electricity;
  • LEDs do not require constant re-adjustment like CFL bulbs;
  • HPS lights run blazingly hot. CFLs runs moderately warm. A good quality LED with built-in heat sinks, will run cooler even than that;
  • LEDs need quite a lot of overhead space, so CFLs still remain a better option for shorter grow rooms. LED grow lights must be kept at 12-18″ above the tops of plants. CFLs can make do with 4”;
  • LEDs will last about 8 times more than CFLs (that amounts to 50,000 hours of use) before they need replacement.

When it comes to lighting there is no “best” option. Every case is unique and you should decide based on your needs and not marketing hype. From a purely technological standpoint, however, LEDs are considerably more advanced (and expensive). If you want more information on the subject, you can check out our article about lights.

Shopping List and Costs

marijuana-grow-cfl-shopping-list

The above simulation was run with just one plant in mind. We wouldn’t advise adding more than two in the same space if growing with CFL. Below, you will find a shopping list of everything you’ll need for a basic CFL grow.

  • CFL Grow Lights (obviously);
  • A grow room/space (2’x2’x4’ and above);
  • Electrical timer;
  • Proper Reflective Material (for your grow space);
  • A growing medium of your choice;
  • Proper nutrients;
  • pH Test Kit.

Generally, 150W of CFLs (a default start) will yield you more or less 30 grams, or a little over 1oz. per plant. Adding more lights will help (up to a point!), but it is ultimately a matter of strain selection. Setup costs may vary according to your location and suppliers. Here is a detailed breakdown of the bulb costs:

  • 40W CFLs for vegging (daylight) $35
  • 42W CFLs for flowering (soft white) $45
  • Sockets, Reflectors & Adapters $45

Electricity costs may vary across states, but on average it is about $0.30/kWh. If you are growing only one plant with an average of 150W, then your monthly electricity costs (for the lights ONLY) should be around $25 (if we assume that the lamps will be on for an average of 18h/day). That’s about $0.80 per day! It is worth mentioning that $0.30 is considerably more than average than the regular electricity costs in the USA. Chances are that electricity will cost much lower than that!

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85 thoughts on “Compact fluorescent (CFL) grow lights

  1. vagellie007 says:

    just wondering guys if i was gonna grow 2 plants in a 32x32x60 grow tent how much and what kind of lights i need? pref do not wanna pay 100 a piece…lol

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  2. david says:

    i am a new grower and have indoor clones four deep purple to be exact. i have them in a 36×36 br closet. i have them under 6 24 inch 75 watt flourescent lights i purchased from kmart.the plants seem to love it they are thriving,is this enuff for them and the main question is r they good for budding as well or do i need different lights for that. flourescent only please help!!!!!

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    Rating: +2 (from 2 votes)
    • John says:

      Hi David. Kind of depends on the color of the light. It should be marked on the bulbs and packaging. If it is around 2700K then you are laughing. If it is too far from this number, then you may struggle a bit.

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      Rating: +1 (from 1 vote)
  3. ATDS says:

    hey iam growing and is a lot of heat bad

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    Rating: +2 (from 2 votes)
    • iveyms says:

      The hotter your plants get the less they will grow, over about 90 degrees they will not put on as much foliage of flowers, so cool it down if possible.

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      Rating: +2 (from 2 votes)
  4. solo 420 says:

    can i use two black lights and a floresent will that work

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    Rating: -3 (from 3 votes)
    • John says:

      No mate, this is a waste of time. This is the wrong kind of light. It would maybe help as supplemental lighting, but not as the only type of light.

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      Rating: +1 (from 1 vote)
    • covert says:

      Black light is a waste of time. wrong color light

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      Rating: +1 (from 1 vote)
  5. Jesse says:

    Yes those should be sufficient

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  6. anon says:

    Ive got two plants and would it be sufficient enough to grow with 4 four foot flourescents. Two are 40w sunshine bulbs that produce 6500k and then i have 1 40w grow lux and 1 40w cool white?

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    • iveyms says:

      They will grow but as they mature they will loose lower foliage and the flowers will not get very big and probably not very tight or full. 600 watts at the least to bring out the best in your plants

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      Rating: +1 (from 1 vote)
  7. Antonio says:

    I use light It Bright brand CFLs 250 watt lamp their red lamp is 2100k the only one on the market in the USA ,blue lamp is 6400k .the best CFLS on the market!..

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  8. blair12 says:

    with light distance you’ll feel a warm spot under your cfl keep the top of your plants just a couple inches under that will be sweet as 🙂
    if the sides of the leafs start to fold up you’ve got heat stress need a little bit more distance . be patient thats enough light just takes a while to grow.
    300waters are easiest to get online 3 105w will do the same job you can flower with them just get either red spectrum or natural day light ones which are good for veg state too

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  9. blair12 says:

    you need 5000 lumens per square foot minimum for a gd plant for normal photoperiod 24h blue for two months then switch 12/12 red leaving the plant in the dark for a full day first can help speed things up
    cfl’s wont start fires my 250w gets a little toastie but not hot even after 18 hours on
    white widow isn’t a gd beginner strain… oh and flush every three weeks screwed my first few grows that way…. it sucked…. lol hope this helps

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    Rating: +2 (from 4 votes)
  10. beast says:

    dude check out thcfarmer,com……NO u cant flower at 24/7 maybe auto,s at 18-24 h/a day…but 12/12 trggers your ladys into flowering and dont interupt light cycle, keep light leaks to a min. and flush before harvest!!!!!

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