Marijuana Cultivation/Fundamentals/Lighting

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Lighting[edit]

Lighting is probably the most crucial element in a grow. If you don't have proper lights then you won't get good results. Unfortunately, this remains true on a low budget and in order to grow indoors you will need to invest in a good light. A general rule of thumb for lighting is 2000 lumens per square foot.

Flourescent[edit]

Flourescent and Compact Flourescent lighting (CFL) is effective for growing marijuana but the spectrum is not ideal. When evaluating these lights you should always look at actual watts and not equivelent watts. These lights come in multiple spectrums but generally they are divided into warm, cool, and daylight spectrums. The daylight spectrum bulbs are ideal but you can use a combination of warm and cool bulbs in equal number as well.

Flourescents lack penetrating power and you will need to keep them within 6 inches of the plant tips except for rooting clones. For rooting clones you will want the lights about 18 inches above the plant tips. Flourescents work well for clones and seedlings that can't take bright or hot lights and also perform well for vegetative growth. Unfortunately these lights simply do not have the punch to perform well for flowering. They can be used in a pinch if you use lots of watts and a shallow grow area by training plants. Many cabinet growers do this with 150w CFL's.

These bulbs require a ballast in addition to a fixture, in CFL bulbs the ballast is built into the bulb.

Mercury Vapor[edit]

Mercury Vapor bulbs are cheap and readily available. But their spectrum makes them a poor choice for growing marijuana.

Incandescent[edit]

These bulbs are everywhere but they are extremely inefficient. You will pay a fortune lighting up these bulbs and reap little reward. These include so called 'grow bulbs' sold in stores.

LED Lighting[edit]

LED lighting has a number of advantages. The lamps have a fixed angle so no reflector is needed, all the light output is directed at the plants. LED lighting runs cool and the plants can grow right up to the lights. These lights produce light in a fairly tight spectrum and lamps are available that can be combined to stimulate all the photo sensitive hormones in the plant.

The downside is that the light spectrums of commonly available LED's aren't perfect for growing marijuana. The number of lumens output by LED's is actually fairly low and LED's are extremely expensive. This technology simply isn't there yet for growers but it will come in time.

Metal Hallide[edit]

Metal Hallide is a high intensity discharge lighting that produces a bluish light. This light spectrum works very well for the vegetative stage of growing but does not work especially well for the flowering cycle which requires more red spectrum for optimal growth. This type of lighting is very popular among growers who often purchase digital ballasts that can switch between these and HPS type bulbs.

High Pressure Sodium[edit]

High Pressure Sodium or HPS is the most popular type of bulb among knowledgable growers today. Most street lamps are HPS lighting. HPS lamps provide an excellent spectrum for flowering and although their spectrum is not quite right for vegetation there are spectrum corrected bulbs with more blue light that work well through the complete grow cycle. There are metal hallide conversion bulbs that work in HPS ballasts, and there are digital ballasts that can switch between the two types of bulb. A 400w HPS light puts out 55,000 lumens and the bulbs become more efficient up until the 600w bulb which puts out 95,000 lumens. The next largest commonly available size of HPS bulb is 1000w but these are less efficient and give fewer lumens per watt than the 600w lamps.

Special Bulbs[edit]

There are a number of special bulbs which you might encounter. You might encounter conversion bulbs, these bulbs allow you to run a lamp in a ballast intended for a different type of lamp. For instance, MH conversion for HPS ballasts and HPS conversion to MH ballasts. Additionally there are spectrum corrected HPS and MH bulbs that add blue and red spectrum respectively to make the lighting work better for growth. Yet other lamps have a reflector built into the bulb.

Reflectors[edit]

There are two reflectors you will certainly want to have. The first is on your lamp, these reflectors vary widely in price but generally you want a polished aluminum reflector that spreads the light well over your grow area. Some reflectors have hoods with an opening to attach ducting in order to keep the light cooler. There are also glass tube fixtures that ducting can connect to 'cool tubes' are the common term used for these.

The other reflector is that around your grow area. The best solution for this is some sort of reflective film such as reflective mylar. Mylar reflects 95% of light back at the plants. In a large space you might want to put the film on cardboard that can be position to enclose the grow to bring the walls in.

If you don't have access to mylar than flat white paint is recommended. Do not use a mirror, mirrors actually absorb light and do not use aluminum foil, it creates hot spots.