Best lighting for indoor cannabis growing

indoor marijuana grow lights

LED lights

Indoor weed growing lighting methods have been changing lately do to technological developments and discoveries of how different light spectrums are used my cannabis plants.

Simply sticking a bright light over your plants for the duration of their grow and flowering cycles is longer seen as adequate.

Smart growers will use different types of lights at different stages of the plants stages.

But to start, lets take a look at the old standby lights that still many growers use – perhaps because its easier to use what you know than contemplate change.


high pressure sodium grow lights hpsMost indoor growing gardens used to use High Intensity Discharge (HID) lamps. The two types most commonly used were Metal Halide (MH) which produce an abundance of light in the blue spectrum promoting plant growth. The other is High Pressure Sodium (HPS) which emit an orange-red glow triggering hormones in plants to increase flowering/budding in plants.

The problems with HID lights is that they consume a lot of electricity for output, produce high operating temperatures, and produce a wider spectrum of light – much of which is not needed or used by the plants. In other words, HID lights are expensive to run, inefficient and a potential fire hazard.

That not to say that HID lights, if used properly won’t deliver great results. They most certainly will. But when you figure in the factors of cost and safety, the newly developed fluorescent grow lights as well as the most recent kid on the block, LED lights, have clear advantages.

Fluorescent lights (CFL)

cfl lights indoor marijuana

125w cfl

High powered fluorescent lights are now specifically produced for indoor gardening. They are available in 2 types – Blue 6400K that emit the wavelength of light needed for plant/vegetative growth, and Red 2700K that emits the wavelength of light for flowering growth.

To produce great crops of marijuana you’ll need both these minds of lights – more of the ‘blue’ wavelength for the first two months and then more ‘red’ when it comes to the flowering phase.

Unlike HID lights, no light falls outside of the needed spectrums which results in less waste and better growth for less power consumption.

With the development of CFL grow lights the need of use of HID lighting has been by and large replaced.

LED (Light Emitting Diodes) lights

The development of LED lights for growing is still in its infancy but holds the greatest promise for the future due to the huge saving in electricity costs.

Currently there is still debate over the preferable diode frequencies (light spectrum), best ratio of spectrum, and wattage of diodes.

Some companies say that the higher wattage per diode the better, with wattages of 2.5 to 3 being promoted.

Other research has indicated that anything over 1 watt per diode and inefficiencies come into play, or in other words, increased power consumption for less out put.

There seems to be a growing consensus that 1 watt per diode is preferable. In other words, for a 300 watt LED light, there should be approximately 300 LED lights.

Beware of 14 watt or 15 watt LED lights with over 200 LED ‘s. They are being promoted widely but when you consider each diode only produces around .006 of a watt, don’t expect vigorous plant growth!

The red / blue ratio is generally 3 to 1 which is considered good for all around plant growth.

Other LED lights offer a wider range of red, blue, orange, purple and dark red, at a 6:1:1:1:1 ratio. Experiments are still on-going to determine the best ratios and colours to include.

So what is the best kind of light to use for indoor growing?

At the current stage of development (2012), CFL still offer the best choice when considering a range of factors such as performance, power consumption, safety and upfront costs.

Using both ‘red’ and ‘blue’ spectrum CFL’s will ensure would have fast growth and abundant flowering.

LED lights win on the power consumption front but the verdict is still out on the performance factor.

The upfront costs of LED lights is considerably higher than other types of lights but users claim that the lights will pay for themselves in time due to less electricity costs to run.

HID lights are the old standby for indoor growing gardens but due to the advancements in CFL’s and LED’s are now largely a thing of the past.

The high power consumption, high heat generation and general inefficiency no longer makes them a viable option.

In short, if you’re the experimental type who likes to be on the cutting edge of technology, LED lights might be right for you – especially if you’ve got some extra coin to invest.

Otherwise you can’t go wrong with specially designed CFL grow lights. Power consumption and start-up costs is reasonable. Good performance is well documented.

During the vegetative phase (first two months depending on strain) the plants should be given 16 to 20 hours of light per 24 hours.

Some say you should grow your crop longer before inducing flowering as it results in a better more potent crop.

But of course it depends to a degree on the strain and opinions differ even among the same strains.

The length of the periods of light should be reduced to no more that 12 hours every 24 hours when shifting to flowering period (which will usually last between 8 and 11 weeks depending on strain).

The plants will continue to grow in the flowering phase and can easily double, or even triple in size.


UK ( click on the image to see specs, prices and availability

cfl grow light cannabis uk

125w to 300w CFL Grow-Lights around £20 each









USA ( click on the image to see specs, prices and availability

250W cfl marijuana grow light usa

250W 2700k cfl $95

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