I am often asked about how I choose lighting and how I apply lighting both in the tank (well outside, but aimed into) and in a grow space in a south-facing window.
First: a few issues that need to be delt with. Artificial lighting is not the same as natural lighting (duh!) in that, outside (or in a greenhouse), under natural light provided by the sun, the sun comes up in the morning - weak and dim. Then it progressively gets brighter as the day goes on (even if it's a cloudy day) until it peaks maybe a bit past mid day. Then as the sun starts to go down, the light dims until darkness arrives at sundown. Get the picture? It's a bell-shaped curve. The only way to tell how many average foot-candles (for us North Americans ;)) is to take repetitive measurements over the day. And then also over the whole year, since day length varies over the year.
With indoor plant lights (of any design) we use timers to turn on and off the lights at a set schedule. Depending on the type of light, full brightness is achieved in a relatively short time (seconds). Phototropic processes begin within seconds to minutes of the full brightness. In other words, flowers emitting fragrance at night, stop emitting the fragrance. Flowers emitting fragrance in day periods, begin emitting, etc. Photosynthesis begins. Growth renews. Day length depends on a timer setting.
Once the lights turn off, the reverse processes occur. Night time fragrance begins. Photosynthesis stops and plant maintenace processes begin. I have personally witnessed Angraecum didieri (night time fragrant species) start it's fragrance within a couple minutes of lights out. This is full fragrance, like fill the room with it fragrance.
Now having described these processes, the next point is that, if an orchid (the subject plant here) is described as wanting high light in the order of 3500 FCs (sorry European readers - thats' approx 35,000 Lux) then, that is being described as a typical day at full brightness. Not really maximum sun, but similar to it. Sort of like: "If you can provide this level of light most days for the peak of the day, that's what it wants." Now with indoor lighting, we have a different scenario as begun above: it's been pretty much demonstrated that a lower level of light (say 1800 FCs / 18,000 Lux) over a steady length of time will equal or approximate this same light regime. For instance, I once placed a Brassavola nodosa (which is notorious as demanding really high levels up to full sun) directly under a bank of t5 florescent lights where I had previously measured a bit over 1800 FCs. The leaves turned red over a period of a couple days. They then progressed back to light green as they got used to the light. I bloom high light Dendrobiums under 1800+ FCs as well. The point here is that, as a grower under artificial lighting, you control: the strength of light being provided, the length of day/night, to a large degree humidity, and you control the plants' access to moisture and nutrients. As "Pot" growers have figured out long ago, super plants are a result of controlling all these factors.
Styles of lighting:
Without trying to start a debate on type of lighting, these are the most common (sorry if I leave out your favorite.)
Regular flourescent bulbs. These are commonly available in just about any store in sizes from 24" to 8-foot. They are referred to as "t12" flourescents (or shop lights) based on the diameter of the tube. They are the fattest bulbs and most common. Their light output per watt of energy consumed is dismal. Some folks still use these, but I suspect they use large numbers of bulbs and plants are located very close to the tubes.
t8 Flourescent tubes. These are the more modern thin tubes seen in many newer kitchens and other flourescent installations. They aren't that bad for plants. There are lots of "colors" available. You can get "daylight", "cool white", "warm", etc. These are very useful for orchid growing with the caveate that they do require close spacing to the tubes. They are way more efficient than t12's and consume much lower amounts of energy per foot candle output.
t5 Flourescent tubes. These are the hottest (pun intended) things around right now in flourescent technology. There are some off-shoots called t6 that are still really t5 in all practical terms. These are really skinny tubes that operate at 95 degrees F (that's the tube surface). Much warmer (or even hotter) than either t12 or t8. The tubes are available in many Kelvin ratings. This is simply a measure of the color of light. For orchids, a range of 5000K to 6500K is ideal. Warmer temperatures (lower numbers) are aimed at triggering flower growth (great for Pot producers, but not necessary for us legal orchid growers).
T5 technology is available in straight tubes (currently 24", 36" (rare) and 48" lengths.) These are nominal lengths. Actual lengths are somewhat shorter. Fixtures tend to be near the stated length of the tubes. They are also available in the "coily tube" bulbs most people might be familiar with. These are commonly referred to as Compact Flourescent or CF bulbs. There are pluses and minuses.
Pluses: You can locate one just about anywhere. It's not much bigger than a lightbulb (depending on output) and can be literally hung from a lamp cord if need be. Can't do that with a straight tube fixture most of the time.
Handy. As well as being able to screw one into a light socket (thus their popularity in low wattage sizes) they are easily replaced when the light gets dimmer.
Negatives: The ballast is built into the base of the bulb. This means if the bulb needs replacing, so does the ballast. They tend to be more expensive than equivilent straight tube fixture bulbs.
They are available all the way up to hundreds of watts, but commonly will be coiled, folded, or otherwise not a straight florescent tube. 2 and 3 bulb fixtures are commonly available that blast light down to even the most demanding plant.
Just remember, every light bulb replacement requires replacing the ballast as well. A much higher cost.
HID (or High Intensity Discharge) lamps.
These have been the mainstay of indoor gardening since, well, forever. They are great. They come in two versions: High Pressure Sodium (warm light) meant for flowering, and Metal Halide (cooler) meant for growth. These lamps run hot - plain and simple. The biggest drawback to these fixtures (if there is a drawback) is their operating temperature. Most indoor grow rooms with these lights are either air conditioned or they are temperature controlled in some way. Also they concentrate the light. That is a plus when you want to light an area some distance from the light source, but can be a problem when trying to grow low light species like Paphs and Phals. Folks that use these fixtures typically employ "light movers" or automated tracks that slowly move the lights back and forth across the plants.
That's pretty much it. There is some experimentation with LED lights, but nothing conclusive, or at least popular.
I am sure I will update this discussion in the future if new technology or observations occur.
4 years ago