suburbanfarmer

This thread is intended to be an exhaustive guide to lighting for people new to growing. Well, it will be exhaustive if I don't get exhausted first : )

In growing plants indoors, in this case marijuana, there are a variety of lighting systems available to use. Each has its benefits and drawbacks, some being price, efficiency, life, usable spectrum, etc. Here is a description of the various types of lights, and what their benefits and drawbacks are, and why they should be used or not.

Definitions:
Wavelength- Technically, the distance between full sinusoidal waves. Practically, used to describe color; for example, 650nm (I think) is red light.
Efficiency- A percentage of how much energy consumed is actually converted into useful energy, With lights, a light with 10% efficiency converts 10% of the inputted energy into light, and 90% into heat.
Color temperature- Measured in Kelvin. This is not a measure of -actual- temperature, as is the Kelvin temperature scale. The higher the number, the more bluish the light. 4000K-7000K is very much on the blue side of the spectrum, while 3000K and under gets progressively redder.

How much light do I need?
The minimum amount of light required by marijuana plants is 2000-3000 lumens per square foot. However, it's not totally accurate, since although you may have a 10,000 lumen light, the amount of light that reaches the plant varies with distance and reflectivity of the grow box. The ideal amount is somewhere around 7000lumen/sqft, and the maximum amount of light is simply determined by if the plants will burn or not; as long as the plants do not burn, as much light can be used as you want.

How far away from my precious little plants do the lights go?
The lights in a grow room should be as close as possible to the plants without burning them. Marijuana loves light; there is no such thing as too much, unless there is sufficient heat to dry out and burn the leaves. Since most people don't have a light meter, a good rule is to put your hand next to the light, and if your hand is uncomfortable at a given distance, chances are that the plants will be too, so move the light up until your hand feels more comfortable. For seedlings and clones, keep the lights further away to start with, because they are very susceptible to burning at these stages.

Efficiency is quite important when choosing a type of light. For example, if you see a 500 watt incandescent light and a 50W fluorescent one for about the same price, you may be tempted to purchase the incandescent one (more power = more light, right?). However, this is a bad choice because incandescent lights emit very little light for the power which they consume. They are said to be inefficient.
I'm not totally sure about the following values; someone posted a thread about the different lights' efficiencies but I can't find it at the moment, so I'm going from memory here.
Incandescents- 17 lumens/watt
Mercury vapor- 45-50 lumens/watt
Fluorescents- 60-70 lumens/watt
Metal halide- ~90 lumens/watt
High pressure sodium- ~107 lumens/watt

Incandescent lights- Incandescents are the most common type of lights in the world. They may come advertised as incandescent, tungsten, quartz, halogen, or simply standard. The important thing to remember about incandescents for growing is this: they suck. Read the 'Why Incandescent Lights Suck' thread above for more info, if you so desire.
There are certain incandescents which are sold as 'grow lights.' They usually have a blue coating and often come in 60W and 120W sizes. While they may be appealing to new growers because of their relatively low price and high power rating, they are next to useless; they produce some light at a usable spectrum, but only have about a 5% efficiency and are all but useless for growing anything but an electricity bill. These lights will put out about 17 lumens per watt.

Fluorescent lights- Fluorescents are a whole lot more useful than incandescents. Their efficiency is pretty good, and are relatively cheap. Compact fluorescent tubes are becoming quite popular with growers because of their good output to size ratio. Compared to standard 4' tubes, compact fluorescent bulbs are very, very small and more can fit into a given area. However, though it is not fact, it is my belief that much of the light from compact fluorescents, especially the spiral kind, is lost in itself. Think about their shape. It is a spiral of glass tubing, and all surfaces of said spiral emit light. What about the center of the spiral? It just shines right into the other side, absorbed by the wall.
For maximum efficiency, I would recommend putting a convergent cone on the inside of the CF spiral, and a divergent cone on the outside, so that as little light from the bulb is absorbed by another part of the bulb. However, losses are still high, considering the overlap of the spiral (where the spiral is wound up on top of itself)
Fluorescents are ideal for small grows on a tight budget, and also good for new growers, since they do not require any special sort of wiring or understanding of the necessary bulbs for a given fixture, and are very widely available.
Fluorescent lights come in many different color temperatures; often the color temps are labeled on packaging as being 'cool white' or 'warm white.' Cool white is more blue, and is good for the vegetative stages of growth, and warm white light is more orange or reddish, and is best for the flowering phase.

High Intensity Discharge (HID) Lighting Systems

Mercury Vapor (abbreviated MV)
Mercury vapor lights are not good for growing. They are plenty bright, and relatively inexpensive, but are not very efficient, and besides that, do not emit light at the wavelengths necessary to support plant growth. Much of the light emitted by MV systems is bluish-white, or ultraviolet.

Metal Halide (abbreviated MH)
Metal halide lighting systems are excellent for use in the vegetative phase of growing. They emit a lot of blue light, which encourages vigorous growth of foliage. They have good efficiency, but can be rather expensive to get started with; fluorescents may seem more appealing because of their lower price, but they are not much different when compared on a lumen-to-lumen cost level. These lights can be used for the duration of a grow, but will most likely result in light, fluffy buds.

High Pressure Sodium (abbreviated HPS)
High pressure sodium lamps emit mostly orange, yellow, and red light, which is ideal for the flowering stage of plant growth. They are generally the most efficient type of light available for any application, barring an extremely high efficiency LED, which I won't even discuss because of their extremely high cost. HPS lights can be used for the duration of a grow. While the plants do take longer to mature and be ready for flowering than with a metal halide light, they produce much more dense and usually larger buds.
HPS lights are generally more expensive than MH or MV systems of similar wattage. They are also the most efficient, and most widely used by experienced growers for their emitted spectrum and efficiency.

Cost of electricity
I will not get into cost calculations for certain wattages of bulbs; you should be able to do that yourself (([wattage consumed] x [number of hours the lights is on per day] x [30 days/month]) / [1000] = total kWh. [total kWh] x [cost per kWh] = total cost of electricity per month.
Generally, you want to get a light with the highest possible efficiency. Electricity will soon amount to more than the cost of buying the light system, so an efficient light will soon pay for the difference between itself and cheaper, less efficient lights.

Conserving Light
What I mean by this is reflecting the light that does not directly strike the plants. This is best accomplished by the new gardener by making everything white; it reflects very well and is cheap. The most reflective material to use is mylar, which is polyethylene coated with aluminum. Don't use aluminum foil; white is more reflective, and crinkled, mirror-like surfaces will create hotspots which will burn certain areas of your plants, while leaving others in the dark. Avoid anything dark colored or transparent for a growing area if possible.

Dispelling Myths
One of the most widely believed and talked-about myth pertaining to lighting is heat emission. I find it rather irritating when people say things like, "Fluorescents emit no heat." I'm not trying to be insulting, just preventing misinformation.
THE MORE EFFICIENT THE LIGHT, THE LESS HEAT EMITTED FOR A GIVEN WATTAGE.
It is very commonly said that fluorescents are low/no heat lights, but this is simply not true at all. People claim that their fluoros put out less heat than an HID system, but that's because a lesser wattage of fluorescent lights is used.
Another myth is that HID lights put out a lot more heat because they 'burn' hotter, and this is why the plants must be so far away from the light. This is simply because the heat from an HID system is concentrated in the bulb, whereas with a fluorescent light, it is spread out over a much, much greater area, and so it doesn't get as hot on the surface of the lights. However, if you've got 400W of fluorescent lights, they WILL put out more heat than a 400W HPS.

Not really a myth, but a sort of false advertisement, are Fluorex bulbs sold on Ebay. Most of these bulbs are advertised as 500W lights that (WOW) only use 65W of power! They are directly compared to a 500W metal halide system as being the same, but for a lower price and power consumption. Lies! This fluorex fixture puts out around 8000 lumens, while a 500W MH would put out upwards of 50,000. Also, they're commonly sold for around $45 plus shipping, and are available at Home Depot for $30. Don't buy into this false advertising, please. Take everything with a grain of salt, to beat a dead horse. Be skeptical, and above all, just use common sense; you'll be amazed how far you can get with it.

Maybe later I'll do another post about where to get lights from cheaply, but finding a good price is really up to you.