The best lighting for indoor growing
Plants produce sugars/energy by photosynthesis. Like our bodies do, a plant uses these sugars and converts them into energy to grow. Lighting is one of the most important factors in growing potent cannabis. Cannabis, if exposed to proper light will grow like a weed, very vigorously. You can use various types of lighting and every type of lighting has its up- and downsides. Before you start growing indoors you must have appropriate lighting. It's best to invest in some proper lamps because your plants (and you) will hugely benefit. Your buds will be heavier and denser and your cannabis will have a higher (psycho)active content.
The following types of lighting are available: HID (High Intensity Discharge), CFL (Compact Fluorescent Lamp) and LED (Light Emitting Diode). HID and CFL are common in use since the 90's. LED lighting is fairly new, but already strongly developed and if you can make the investment it's probably the best option as it will save you a lot of energy. A (sudden) high energy use is a red alert. (at least that's one of the methods how they track down the larger growing facilities here in The Netherlands)
LED lighting, these days, can provide excellent wavelengths for optimal growing
HID light in a growroom, a warm color
CFL lighting, cheap lights but with shorter range output.
If you are going to grow indoors, measure your growing space. 2000 lumens per square feet (20k lumens per square meter) is about as low as you want to go indoors. If you get under this mark, plant growth will certainly 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 per square feet should be a good target, and 3000 is optimal if your going to inject or enrich CO2 levels (more on that later).
High Intensity Discharge (HID) lamps are the best solution for most indoor growers as LED lighting is substantially more expensive and CFL lamps need to be closer to the plants because their output has a shorter range.
HID lamps come in 3 basic flavors: High Pressure Sodium (HPS), Metal Halide (MH) and Mercury Vapor. Metal Halide is an improved spectrum, higher intensity Mercury Vapor design. HPS is a yellowish sort of light, maybe a bit pink or orange. Same as some street lamps.
HPS lamps can be used to grow a crop from start to finish. Tests show that the HPS crop will mature 1 week later than a similar crop under MH, but it will be a bigger yield, so it is better to wait the extra week.
Fluorescent and Mercury Vapor (MV) lighting
The easiest HID to buy, and least expensive initially are the fluorescent and mercury vapor (MV) lamps. MV will output about 8000 lumens per 175 watts, and 150 watts of HPS puts out about 15k lumens, so HPS is almost twice as efficient. But the color spectrum from MV lamp output is not as good. HPS is high in reds, which works well for flowering, while the Metal Halide is rich in blues, needed for the best vegetative growth. Unfortunately, MV lamps provide the worst spectrum for plant growth, but are very inexpensive to purchase.They are not recommended, unless you find them free, and even then, the electricity/efficiency issues outweigh the initial costs saved.
400 watt HPS will output around 45k lumens. For every 500 watts of continuous use, you use about $20 a month in electricity, so it is evident that a lamp taking half the power to output the same lumens (or twice the lumens at the same power level) will pay for itself in a year or so, and from then on, continuous savings will be reaped. This is a simple initial cost vs. operating costs calculation, and does not take into account the faster growth and increased yield the HPS lamp will give you, due to more light being available. If this is factored into the calculation the HPS lamp will pay for itself with the first crop, when compared to MV or fluorescent lamps, since it is easily twice as efficient and grows flowers faster and bigger.
The benefits of LED lighting
Modern LED lights which are specifically designed for growing send at light at such a specific wavelength that the plants can use ~95%-98% of the light emitted for photosynthesis. Also LED doesn't give off much heat, and they have an operating time of at least 50.000 hours which means that you can grow over the course of 5.5 years literally non-stop, 24/7/365 without having to change lamps. Modern LED lights will yield even better results than much more energy consuming HID lights. You can save about 55% energy. A typical 400 watt HID light would be consuming 180 watt when using LED. Do not buy the cheap Chinese growing lights though, the usually don't emit the right wavelengths.