In an ideal world, all marijuana plants would grow outside, bathed in glorious sunlight. In the real world, there are numerous reasons for growing marijuana indoors, particularly for people who live in cooler climates. That being so, the aim of any lighting system is essentially to mimic the action of sunlight.
The Main Kinds of Lights
High-Intensity Lamps (MH or HPS)
MH (Metal Halide) lamps can only be used during the growth phase whereas HPS (High-Pressure Sodium) lamps can be used throughout the plant's entire life-cycle. These lamps are generally cheaper than LEDs but more expensive than CFL lamps. Likewise they are less energy-efficient than LEDs but more economical than CFL lamps. Unlike LEDs, MH and HPS lamps both produce heat, which has implications in terms of safety, in particular it means that growers will need to give serious thought to ventilation. Both kinds of lamps need a ballast, which will generally be provided upon purchase. These days, sellers will generally provide a digital ballast which is vastly superior to the traditional magnetic ones. It's worth checking both these points.
LEDs (Light Emitting Diodes) are becoming popular for all kinds of uses due to the fact that they can deliver great performance for very little electricity. They also stay relatively cool to the touch when in use, which has benefits in terms of safety and also promotes comfort as it keeps the overall temperature down. The key point to note about LEDs is that quality LEDs are more expensive to buy than the other types of lights available. In addition, brand-name LEDs can be counterfeited. This means that it is crucial to research both your brand and your seller.
CFLs (Compact Florescent Lights) are probably the best choice for very small-scale growers, who just want a few plants for occasional, medicinal use. They are
affordable to buy and easy to use. As fluorescents, the heat output is fairly low, so while ventilation will probably still be required, it will be less of an issue than with the high-intensity lamps. While these lights are only really suitable for small scale growing, they can still produce great results at a reasonable cost.
Lights and Safety
If you are using CFLs, MHS or HPSs then your lights will generate heat. This means that ensuring adequate ventilation is as much a matter of safety as it is of plants getting the energy they need. You will also need to think about flammability. In simple terms, you need to make sure that nothing flammable can touch your lights.
Lights (and Reflectors) Need to Be Replaced
When you buy lights (or reflectors), they will generally come with guidance as to how long they can be used before they need to be replaced. References to “a year” should generally be taken to mean one growing cycle of 1172 hours. All manufacturer guidance is based on the assumption that the lights are being properly looked after. In particular they need to be kept clean, as well as giving them a regular physical clean, using filtered water will go a long way to stopping mineral deposits building up on them.
Using Light Effectively
Make sure that the plants are positioned so that they can get the light they need. This includes
making sure that there is still plenty of space between them as they grow. Remember you are looking to light your plants not your walls. Ideally you should make your walls do double-duty as reflectors by covering them in reflective material.