Here is a guide to lighting and light bulbs and what they will do for your plants. (feel free to suggest any changes if you see an error ) I didn't write it all.....just compiled it and added a bunch. Indoors, 2000 lumens per sq. ft. is about as low as you want to go indoors. If you get under this mark, plant growth will definately not go as fast as possible, and internode/stem length will increase. Also, light distance to plants will be much more critical. Daily adjustments to the lamps will be necessary, meaning you get no vacations. 2500 lumens psf should be a good target, and 3000 is optimal if your going to inject or enrich CO2 levels. High Pressure Sodium - or HPS lamps emit a pink or amber light. They are used generally for lighting parking lots and other areas where the color of the light is not all that important. HPS lights are much more efficient than MH ones, producing more light and less energy consumed. They are often used alone with no detrimental effect on the plants, and will promote faster plant growth than MH lamps during both vegetative growth and flowering. Combinations of bulbs are _NOT_ required, as the HPS lamp does produce all of the light spectrums necessary for healthy growth. There is a relatively new type of HPS lamp that has become available. It is called the... Son Agro lamp Basically the designers of this special lamp took a 400w HPS lamp, and added another 30W element to it, However, this new element puts out blue light, to help fill in the parts of the spectrum that a standard HPS light is missing. Metal Halide - Metal halide (MH) lamps can be used for vegging and flowering (but primarily vegging), but there are two problems that they have when compared with high-pressure sodium (HPS) lamps. The first is that they don't emit as much total light. HPS lamps emit more than 20% more light, so MH lamps are not as intense when covering the same area. Second, they do not emit as much orange and red light as HPS lamps. These spectrums seem to promote flowering. However, MH lamps do have several advantages over HPS. First, they are less expensive to purchase. Second, the light does not have a really weird telltale spectrum. It looks white, not pink or amber/orange. Third, the lamps emit more UVB light than HPS lamps, although still in very small amounts. The amount of UVB light plants receive is directly related to the quality of the harvested buds. The more UVB, the higher the quality. Buds grown under MH light will not be as big as buds grown using HPS lighting. However their quality will be as good or better. Compact Flourescent - Or CFL . This type of light is perfect for seedlings, cuttings, and clones. They can be used for vegging and flowering but are not as effective as high intensity discharge lights like the HPS. Fluorescent lights are low intensity and need to be placed quite close (2-3 inches) to be very effective. They are a poor light source for flowering and budding primarily because of their low lumen output. One advantage of CFLs is that they produce very little heat enabeling them to be kept quite close to the plants. But even with cool bulbs, always remember a fan for circulation. CFLs come in both warm and cool spectrums. A mix of both is ideal but warm is generally for flowering and cool for vegging. They are excellent for side lighting and can be found relatively cheap and many grocery stores and the like. Flourescent Tubes - Fluorescent tubes have been used to cultivate and flower marijuana. However, buds grown under these lights are usually fairly small and loose. The reason for this is that the intensity of the light, that is the amount of light that is produced by these lamps, is relatively low. In addition, the light is produced over a large area. The result is a lower amount of light spread out over a large area, so the amount reaching the plants is a small fraction of the amount the plants receive from a metal halide (MH) or high pressure sodium (HPS) lamp (and even Compact varieties) Fluorescent tubes are more expensive than HPS lamps, too. The initial cost of a fluorescent is less than a HPS. However, when the cost of light is considered the cost picture changes. HPS lamps emit 2 1/2 to 3 times the amount of light per unit of energy consumed. The efficient HPS lamp is much cheaper over its life than a fluorescent tube. Although you can grow marijuana using a fluorescent, you will produce a much higher yield of better grade grass cheaper and easier using an HPS lamp than a fluorescent. Incandescents - Not generally used in Marijuana growing. The common incandescent light bulb emits some of the frequencies of light the plant can use, but it also emits a high percentage of far red and infra-red light which cause the plant to concentrate its growth on the stem. This results in the plant stretching toward the light bulb until it becomes so tall and spindly that it just weakly topples over. There are several brands of bulb type. One is the incandescent plant spot light which emits higher amounts of red and blue light than the common house light bulb. It is an improvement, but has it's drawbacks. Tbe bulb is hot, for example, and cannot be placed close to the plants. Consequently, the plant has to stretch upwards again and is in danger of becoming too stretched and falling over. The red bands of light seem to encourage stem growth which is not desirable in growing marijuana. The idea is to encourage foliage growth for obvious reasons. Mercury Vapor - Not generally used for marijuana growing. Mercury Vapor lamps are less efficient than the fluorescent (FL), and can not be positioned as close to the plants, so the plants will not be able to use as much of the MV light. The light distribution is not as good either. MV lamps simply are not suitable for indoor marijuana gardening. Use flourecent, MH, or HPS lamps only. Halogen - Not generally used for marijuana growing. High pressure sodium (HPS) lamps emit at least seven times more light than halogen lamps. A garden growing under a 1000-watt HPS lamp is expected to yield one pound or more than one under a 1000-watt Halogen. The initial cost of the halogen bulb is much cheaper than an HPS lamp. However, when the cost of generating light is considered, HPS lamps are much cheaper. For every dollar you spend on electricity for lighting using a halogen bulb, you pay only 14 cents or less using an HPS lamp. In addition to the cost of electricity, consider the space being used and most importantly your time. You expend essentially the same effort to produce 100 grams rather than 400-500 grams. That alone makes a small harvest considerably more expensive than a large one.