I did a lot of poking around on the topic of artificial lighting in the last six months or so. An awful lot has changed in the last 5 years and LEDs are rapidly emerging as the single best solution for most people. I'll summarize what I learned.
Chlorophyll in all plants - aquatic, terrestrial, epiphytic, whatever - absorbs mainly photons with energies near two specific wavelengths. Such light appears bluish and pinkish to us. Other wavelengths are not used at all and it is a waste electricity of to produce them.
Plants grow great under pinkish and bluish light but look weird to us, so most hobbyists are willing to provide light at other wavelengths for aesthetic reasons.
Metal halide (MH) bulbs produce adequate light for plants. They are expensive, extremely hot to run, and use much more electricity than other kinds of growing lights, much of which is wasted producing heat. They will produce third-degree burns in humans in less time than it takes to withdraw your hand. They will explode if a drop of water hits them when lit, showering near-molten glass all over you and your plants. Their light output declines with age. People make the argument metal halide both lights and heats the growing space during winter, but it costs much less to use different light sources plus heaters to accomplish the same thing. Almost nobody starting from scratch would use metal halide lights nowadays.
Incandescent lights can provide adequate light for plants. They are also hot and cost a lot more to operate than fluorescent lights. Few people starting from scratch would use incandescent lights.
Fluorescent lights of all types and sizes (standard, CFL, T5, T8, T12, spiral...) can produce adequate light for plants. CFL stands for Compact Fluorescent Lighting. These use much less electricity than similarly-rated incandescent lights. The T number refers to the diameter of the tube. T12 is the standard size for overhead lighting; these tubes tend to be the least expensive initially. Tube sizes are not interchangeable in fixtures. All white fluorescent lights emit many wavelengths, including those not used by plants, so electricity is being wasted on producing useless wavelengths.
Among other qualities, fluorescent lights are rated by something called color temperature, reported in Kelvin units, K. This is a rough approximation for light wavelength produced by the fixture. Around 6,500K is needed to grow plants. This is often labeled as "daylight" but you must look at the K rating, because different manufacturers use different terminology. Aquarium fixtures are often used by plant growers. 10,000K tubes provide a brilliant white light that is great for viewing fish but poor for growing plants. "Cool White" tubes have a K rating too low for plants. The K rating is often printed on the tube and is always on the package in the US.
All fluorescent tubes diminish in output as they age. The plants will notice this before your eye does. Most people recommend changing fluorescent lights every 9-12 months because of the diminishing light output.
Standard 4 foot long T12 double-tube shop lights with 6,500 K bulbs are adequate for plants. This is a very low-cost solution to install, but when factoring in electricity cost and fixture lifespan, it is no longer the best. Higher wattage tubes are better than lower. The plants will have to be quite close to the tubes. They produce some heat but it would be unusual for a person to be burned by the fixture.
T5 lights are often used for growing plants - aquatic and otherwise. T5 and their fixtures are more expensive initially than T12, but are supposed to wind up using a lot less electricity for the output over time, so they are supposed to wind up costing less. They produce a fair amount of heat, enough to be a problem for some aquarists and non-aquatic plant hobbyists. Fixtures may burn humans.
CFL lights rated 6,500K provide adequate light for plants. They produce less heat than T5 tubes. A 200 Watt equivalent spiral CFL is available that fits into a standard-base clamp-on shop light with a reflector. I have used this solution to bring aquatic plants needing extremely high light intensity through the winter indoors: water hyacinth, hornwort, Azorella. T5 fixtures are supposedly cheaper than CFLs overall but I was not willing to accept the hot fixtures. I can touch the 200 Watt equivalent spiral bulb. It is clearly hot, but there is plenty of time to remove my hand before being burned. The clamp reflector does not heat up enough to burn my hand. These bulbs also need to be close to the plants.
Light-emitting diodes (LEDs) use a different technology from other fixtures. Each LED emits only one wavelength of light. If LEDs/wavelengths are chosen properly, plants can grow under these lights, and electricity will not be wasted on useless wavelengths. By their nature LEDs last an extremely long time with minimal decrease in light output. The lights themselves emit little heat, but they need a transformer to convert household electricity into a voltage they can use. The transformer produces some heat, but generally not enough to burn a human, and it is well away from the plants. LEDs fixtures initially cost a lot more than fluorescent fixtures and tubes, but the electricity savings are supposed to be large enough that the payout period is a year or less. I know a large aquatic nursery owner who switched his entire operation from CFL to LED and the payback period was less than a year.
Commercial vegetable production is being switched to LED lighting because electricity costs are much less over time. Gigantic warehouses are illuminated in pink and blue only. These warehouses are tightly sealed to prevent entry of pests, so insecticides need not be used. Plants are grown hydroponically in nutrient solutions adjusted daily based on analysis of random leaf samples.
White aquarium LEDs seem adequate for some plants, but how to measure intensity of light produced and how to decide which fixtures work well are still not well understood. Aquarium LEDs generally provide neither wavelength nor light intensity information.
We tend not to like the look of only pink and blue LEDs, so fixtures are available containing white as well. People posting to this board sell them. I have not tried any of them but I would expect they work well.
To sum up, if you have minimal money available, you probably shouldn't be growing plants under lights, especially orchids, but that never stopped me when I was dirt poor. If you want to minimize initial outlay, or you don't care about electricity cost now or in the future, use a T12 or CFL system with 6,500K color temperature bulbs in the highest Watt equivalent you can get, and change your bulbs every 9-12 months. Anybody else should use LEDs designed for growing plants.