A Quick Guide to Lighting for Indoor Cannabis Grows

For those of you who don’t remember your school biology classes (well the botany ones at least), plants need light to grow. This self-evident fact that we all take for granted maybe needs explaining in a little more detail if we are to replicate the natural environment in an indoor grow room.

Plants are autotrophs, which means that they make their own food without consuming other plants. They do this through a process called photosynthesis whereby they convert light energy into chemical energy.

Sacs within the green double-layered membrane inside the plant green tissue capture light energy and use it to produce ATP and NADPH. NADPH converts carbon dioxide into the high energy sugar and other molecules needed for plant growth

It goes without saying then that a plant without sufficient light will not grow – and may even die – as it needs light or it will starve. But there’s more. Some plants are shade tolerant, and do best in indirect sunlight such as inside your house. Others – especially those that go from seed through to flowering, producing seed and dying – in one season (annual plants) often need a great deal of sunlight to photosynthesize and achieve all this growth in one short season. Cannabis is this kind of plant: its extremely light hungry!

Science shows us that sun light is made up of colours from across the spectrum at different wavelengths (nm). Research has identified which wavelengths the cannabis plant uses for growth and which for flowering.

Because you can never replicate the intensity of light in indoor gardening that you will find in natural sunlight, it is important that the light you give is sufficient within these wavelengths. Put simply, your 90 watt standard light bulb may seem to you to light your living room, but it will not produce enough usable light for the cannabis plant to convert into NADPH.

If you want your plants to grow, and flower, to their full potential it is essential to invest in specialist grow lamps for the indoor grow room.

Overview of the different kinds of cannabis grow lighting

The majority of indoor growers will use an HID Lighting System. It was the development of these back in the early 1990s which made the indoor grow room a practical possibility. There are now however alternative set-ups available and we’ll run through them all here:

HID Grow Lamps HID Lights

High Intensity Discharge light systems have been the major force in the possibility of growing cannabis indoors over the past 25 years. The system consists of a “ballast”, a reflector and a specialist light bulb which together produce a highly charged light source.

HIDs, as the name suggests, emit large amounts of light at high density

A HID grow lamp system can range from the economical $100 dollar kit up to $1000 dollars for high end items. You can buy a complete lighting kit, or put together your own system (almost all ranges are interchangeable except some specialist systems e.g. Gavita). The system consists of a ballast which converts your domestic electricity into the power supply for the large gaseous bulb and a reflector with integral bulb holder. HID lamps produce enormous amounts of light (and indirectly heat) and enable cannabis plants to really flower to their full potential. Much of the equipment and methodology of indoor growing is based on the assumption that you are using this sort of lighting.

Advantages to using HID grow lights:

  • produce a large amount of light for the plants to convert into cell growth and flower development
  • proven to work
  • widespread knowledge and advice available
  • budget options available as starter kits


  • use a larger amount of power both directly and indirectly (through larger extraction units etc)
  • cause power spikes in electricity consumption when a number of lights and extraction all kick in at the same time. It’s said that some police forces look for such power increases as being suspicious. (This can be avoided by staggering the switching on times)
  • HEAT: these add a substantial amount of heat to a confined grow space. Much of the additional climate control equipment necessary is to reduce temperatures down to an acceptable range. Dealing with, and monitoring your heat levels becomes a part of your growing technique. And if you live anywhere where outside temperatures rise during the summer, you can forget about indoor growing.
  • Heat signatures have been picked up using thermal cameras on police helicopters. Some grows have even been spotted due to snow melt!
  • The initial outlay may be low, but the shelf life of a HID is short: at 12 hours daily, expected bulb life is said to be 3 years. Most growers would however replace bulbs after 1 ½ years. Ballasts etc. also deteriorate in efficiency so rather than just replace bulbs, long term growers replace the whole system at this time.

Can you use CFLs to grow cannabis?Growing autoflowers under CFLs

There’s a lot of argument about this: CFL lights have their adherants, who claim they are a low-cost and low energy consuming means of growing. Opponents believe they don’t pack the necessary punch to produce good yields, or that you would need to use so many you may as well have invested in a “proper” lighting system in the first place.
CFLs produce a low level of light and less heat than HIDs, and this light is spread over a wide area, meaning that the grow light has to be kept close to the plant in order for it to get the right concentration of light. This works in the CFLs favour for use as a cuttings or seedlings grow light: the relative lack of heat means that because the plant is close to the marijuana lights (20cm or 8”), it experiences less stretching than it would at a distance from a heat producing HID.

As a main source of lighting for marijuana however, most find that it lacks sufficient power for good vegetative growth and certainly for good flowering.
Buy the cool white type of CFLs for growing.

Advantages to using CFLs to grow cannabis:

  • low purchase cost: you can add more bulbs as you progress into flowering
  • low running costs: these are energy efficient
  • easily available
  • great for restricted height grows. If your grow space is limited, these can be placed very close to the plant.
  • stimulates short node space and therefore better bud formation

T5 Grow Lights Quantum Bady Boy Review

T5s are the long fluorescent tubular bulbs measuring 5/8″: you may have had something similar in your kitchen / office in years past. T5 Grow Lamp kits feature a reflector hood capable of holding several T5s side by side. Many growers view them as the logical development of the principles of using CFLs. They have the same energy efficiency, low heat production, low grow room – but at the same time the same disadvantages: most are sceptical that they emit sufficient usable light energy for the plants to photosynthesize at the maximum potential rate.

That said, we have seen some amazing grow reports using specifically designed T5 lights, such as the Quantum Badboy. But at the price of a Badboy, we’d advise going for a LED Grow Light system instead!

LED grow lights and cannabis. Do LEDs work?

LED grow lights combine high efficiency with low energy consumption. A 10w LED lightbulb can light your living room as well as a traditional bulb drawing 60w. Because LED grow lights consist of a large number of LED chips (diodes) each configerated to a specific light wavelength, it is possible to dial in accurately the light spectrum most advantageous to the plants: ie to supply almost twice as much light at the red end of the spectrum (640-660nm) as at the blue, and use no (or almost none) light which won’t be used for photosynethesis (see PAR diagram above). Not only do these lights draw less electricity they don’t make “wasted” light.

The designers of the first LED grow lights understood these principles, but unfortunately released models before research allowed them to refine and develop the technology. Growers invested in models with 1 watt diodes and a straight single colour blue and red spectrum and the results were disappointing. LED lights now use 3 watt, 5 watt and cob chop diodes, and the spectrum ranges over a wider range. Resulting harvests are comparable with HID grow lamps with a direct 25% saving on power used solely for lighting plus indirect savings on smaller extraction units etc.

Advantages to using LED grow lights:

We actually think LEDs might be the indoor grower’s problem solver! Read why we believe LED grow lights are best for cannabis here.


  • High initial cost
  • Some differences in growing methodology needed to make LED grows truly successful.