CFL Grow Lights


Although this website is focused on the LED grow light, it would not be complete without also looking at one of its close competitors, the CFL grow light. Nowadays you can get compact fluorescent lighting that can cover any party of the visible light spectrum and which is powerful enough to be used as a grow light. There are several advantages of using CFL grow lights over the more traditional HID grow lights. CFL grow lights are cheaper, and much more energy efficient, they don’t have to be actively cooled, they have an integrated ballast, and they are useful for use within small spaces, such as grow tents, since plants can grow quite close to them without suffering the negative effects of excessive heat. As you can see, many of these advantages are similar to those of LED grow lights.

Image representing the colour temperature scale (numbers in Kelvin units)

The Kelvin Scale

Unlike LED grow lights however, where you can identify the specific wavelengths of light being emitted, CFL grow lights emit over a wide range of wavelengths that combine together to produce a ‘shade’ of white light. Depending on their construction, different CFL bulbs will emit different colour ranges thereby producing different shades of white light. Due to this limited control over the exact wavelengths emitted from the grow light, a different scale called the Kelvin scale (K) is used to represent the type of CFL grow light. Lower Kelvin CFL bulbs emit white light containing more red wavelengths of the visible light spectrum, so are generally used for flowering regimes, whereas higher Kelvin bulbs are associated with white light that contains more blue wavelengths and so are often used for vegetative growth.

Buying a CFL grow light

So the first thing to consider when choosing your CFL grow light is whether you need it for vegetative growth or to encourage your plants into flowering and fruit production. Once you have decided on which colour bulbs you are looking for, the next task to consider is the amount of lumens or light intensity you need to get optimal plant growth. The sun produces approximately 98000 lumens / m2 (10,000 lumens / ft2 if you are an American) on a perpendicular horizontal surface at sea level. Obviously the sun is not always unobstructed and exactly perpendicular to the surface of the earth but this at least gives you an idea of what ‘perfect’ lighting conditions would be like in nature, and so it makes a reasonable target to aim for in your grow area.

Different CFL grow lights produce different amounts of lumens. However, it is important to remember that this is the total light output from the bulb and only a proportion of these lumens will hit the area that we are targeting even with reflectors and reflective Mylar sheet-covered walls. Here a good estimate to use is to assume that only 90% of the lumens emitted from a bulb will hit the plant canopy and be used. Obviously this assumes that the grow light will be hung high enough so that the light covers the whole of your growing area, but then close enough to the plant canopy to maximise light exposure without the plants getting too hot (it is also recommended to hang the light using a retractable system so that the light can be raised as the top of the plant canopy rises).

OK so now we know what we need in terms of the type of CFL grow light and how bright it should be. So let’s take a look at some of the CFL grow lights available.

Image of a CFL Grow LightIf you want to avoid spending on two different types of CFL grow light, one for vegetative growth and one for flowering induction, this Giant Eco-Grow light has been configured to emit over both the red and blue ranges, essentially covering the whole visible light spectrum. Remember though that you will be sacrificing a little on both optimal plant Image of the base of a CFL grow light showing the Edison screw fittingvegetative growth and flowering induction for the sake of economy, so it just depends on what is more of a priority for your circumstances. This bulb is a giant (both in make and in size!), but it can still be used in the standard E40 (40mm Edison Screw) ceramic grow light holder that one usually uses for HID lamps. 300W CFL bulbs emit about 22,000 lumens (approximately 20,000 lumens after estimated losses) so if you have a 1 square metre grow area you will need 5 of these goliaths to hit our target of 98,000 lumens per m2.

That seems like a lot of light bulbs for a small area but remember that is for hitting a target equivalent to perfect sunny conditions for the whole day, each and every day! How many times (especially here in the UK!) have you seen the sun come out and stay out each and every day, and fix itself permanently at the highest point in the sky? You haven’t. The point is that plants will grow well with a lot less lumens than our target, so lower numbers of light bulbs will work well too – our target provides a good point of reference though. If you don’t already have the fitting, the CFL grow light is also available together with the E40 lamp holder and reflector (see table below).

Other CFL grow lights with different characteristics (wattage and colour temperature) are available but their appearance is very similar to the one pictured above, so I have not included any pictures of them here, instead, they have been summarised in the table below – click on the name in the table to take you directly to the product listing on Amazon.

CFL Grow Lights

 WattageColour TemperatureLumens (approx.)Sold on
B00KW640RG300WBlue 6400K
Red 2700K
B008A5XD4W300WBlue 6400K 22,000
B00L71Z9BG300WRed 2700K 22,000

 Posted by at 5:29 pm