Growing Autoflowers Under CFL: Grow Guide

cfl autoflower grow guide

CFL autoflower grow guide or compact fluorescent lights are known as one of the most commonly used types of lighting for growing cannabis especially autoflowering cannabis plants. Growing autoflowers under CFL is one of the most efficient and safest lighting solutions for growing weed.

How CFL Autoflower Grow Guide Lights Work

CFLs work by using fluorescence. A glass inside the fluorescent glass tube contains gas. This gas becomes excited when electricity moves through it. As the gas becomes excited, it creates ultraviolet rays that move through the phosphor-coated walls of the glass.

As the light moves through the walls, the phosphor begins to fluorescence and produce visible light. The science used in CFLs is not new and in fact, this is seen in fluorescent T12, T5 and T8 tubes that have been used for many years. But compared to previous models with a large ballast, newer versions come with smaller ballasts located just above where the light and socket contact.

Why CFL Lights on Autoflowering Strains

Most cannabis growers think that CFL lights are inefficient because of their light output per watt. Growers believed that this quality of light will only grow very small plants, but this is not always true.

Fluorescent lights have a much higher photoactive radiation index compared to HID lights used in growing cannabis. This could only mean that light coming from CFL lights is needed by plants and there is only a small amount of light created and lost because plants are unable to utilize that light.

There are a number of spots along the spectral scale that cannabis uses light. For instance, the green light is rarely used as well as the yellow light. Compared to HPS lights that give off yellow light, CFL produces red or blue depending on the type of bulb. These colors will be able to produce the same yields or maybe improved yields.

Different CFL Lights and Efficiency

CFL lamps are available in various shapes as well as wattages and lumen outputs. However, not all of these have similar efficiency ratings. When you sum up all the shapes of CFL bulbs, you will get spiral and tubed bulbs.

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Tubed CFL bulbs are longer and thinner while the spiral bulbs are shorter but wider. All-in-all, you just need to select the bulb that will suit your needs.

When it comes to efficiency ratings, a bulb with a tube or spiral shape won’t matter because the wattage is the most important component and usually the most calculated is the lumen per watt ratio of the bulb. Consider the following efficiency ratings of sample CFL bulbs. This will help you find the right light bulb that will provide the best light output for your cannabis growing area.

13 825 63
26 1610 61 l
42 2700 64
45 2800 62
85 4250 50
125 7000 56
200 9500 47
300 13975 46


This table shows the most efficient CFL lamps which are bulbs from 12 W to 45 W however, 13 W bulbs may be too inefficient. You might need more 13 W bulbs to cultivate cannabis. The best CFL bulbs to grow cannabis are the 42 W bulb because this is the most efficient therefore will be able to grow the largest plants.

42 W CFL buds give off 2700 lumens, therefore, you just need two of these to maximize light and to get the best yield per bud.

Cannabis plants require anywhere from 5000 to 10000 lumens per square feet of growth. Therefore you must measure your area to find out how much light you need to grow your plants. For instance, your growing area is 10 square feet, therefore, you need around 20 CFL bulbs to provide the ideal lighting for your plants.

Where to place your CFL lamps inside a growing room? Usually, growers just place these around the growing area to get the best results.

Do CFL Colors Matter?

Cannabis plants require different types of light during their different stages of growth. During the seedling and the growth stage, plants need more blue light. During the flowering stage, plants will need a more red light. However, plants may also use all the colors in the light spectrum except green.

How do you pick the right color temperature for your cannabis plants? There are two categories measured in degrees Kelvin or K. The 6500 K is for plants in the seedling and the growing phases. For the flowering stage, use 3000 K to 4000 K bulbs. These bulbs will have varying spectral outputs and this will give your plants more diverse light that they can use.

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Advantages of using CFL Lights

CFL lamps are perfect for autoflowering cannabis as well as other types of marijuana plants but the downside is, you need a lot of them. These lamps should be placed around the room as well as around your plants to get the best results. CFL gives off low amounts of heat, therefore, you can place this near your plants even within a distance of 2 inches.

CFL lamps are cheaper compared to expensive LED lamps and HPS lamps. These are also easy to replace since most hardware stores and houseware stores have CFL bulbs.

CFL bulbs don’t need special hardware to install. These can fit in E27 bulb sockets, therefore, it is also easy to find lighting hardware from local stores.

CFL lamps are available in different color temperatures. You can easily find the ideal bulb color that will fit the growing phase of your plants.

This type of lighting has high PAR efficiency and will stay cooler compared to HID bulbs. This way, your plants will remain cool and the growing area won’t grow too hot even when there are several lamps used.

CFL lamps can be easily placed all around the room. You can place these along the ceiling of the growing room or cabinet, along with the sides of the cabinet as well as the bottom part of the room.

Finally, CFL lamps won’t cost a lot of money to run. Compared to HPS bulbs that are too hot, these will never leave a hole in your wallet even if you light these up all day.

The Disadvantage of using CFL Lights

Using CFL lamps also has a few setbacks. CFL lamps with higher wattages are inefficient compared to those with lower wattages.

To get the most out of using CFL lamps, you may need many bulbs situated along different areas of the room. And compared to LED bulbs that last for years, CFL bulbs have shorter lifespans.

Tips for using CFL Autoflower Grow Guide

  • Distance

Place CFL bulbs near your plants. These should be placed 2 inches between the plant and the bulbs. Depending on the size of your growing area, plan on where to place these bulbs in the most efficient manner.

  • Number of lamps
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You must not just rely on one large bulb in the middle of the growing area because this is not going to be efficient. It will only light plants parts along the top of the canopy. Install several bulbs on top as well as the floor pointing to the bottom section of the plants and along the sides of the plants to get the best results.

  • Energy saving lamps

There are energy-saving CFL bulbs available in the market. These should be your choice if you plan to expose your autoflowering plants to non-stop 24-hour lighting or 20/4 light/dark. Energy-efficient bulbs will let you light your growing area without spending too much on electricity.

  • Install a timer

To get the most out of using CFL bulbs and even other types of lighting, use a timer. With a timer, you can efficiently power off your lamps at a certain time of the day. A timer will also let you save power and will allow you to use special lighting schedules. However, autoflowering plants don’t need any lighting schedule since these will automatically flower at a certain age.

  • Prune your plants

Removing large fan leaves will help light penetrate the inner sections of the plant. Pruning weed will also help reduce moisture or humidity inside the plant structures.

Remember the following when using CFL Autoflower Grow Guide

Cannabis plants are very sensitive. If it lacks light, it will tell you that it needs light by stretching. Some plants can stretch up to double its height just to get more light. If you notice stretching in your plants, adjust your lighting. Keep CFL bulbs near plants or at least two inches away from plants.

But cannabis plants can get light burn as well. Sometimes, growers can get too overly worried about their plants and install too many bulbs or lamps inside a very small area. This is bad for your plants and can even cause burning. If you are growing autoflowers under CFL and you notice drying or burning, remove a few lamps.

Hold your hands against the lamp and if you feel hot, your plants will surely be hot as well.

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