Many people look at this photograph of the lobby of a luxury resort hotel in Puerto Rico and think it was shot using natural light, because it is so open and bright and natural looking. What's funny, is that the opposite is true; to get such a natural looking picture, you often need to use a lot of artificial light. This shot used five separate studio-sized flash heads and power packs, plus all the assorted soft boxes, umbrellas, scrims, and other light modifiers, plus stands, booms, clamps, and ballast. When it's all set up, it looks like a movie set. The trick is setting all this up quickly and efficiently, and knowing how to make the lighting equipment work its magic.
Some photographers, including architectural shooters, claim that natural light is the only way to go when taking a picture, but there is no possible way to capture this open, bright, airy space using just natural ambient light. Here's why:
(This is an example of a BAD photograph, in case you arrived in the middle of this discussion. I wouldn't want anyone to think this is my work that I'd like to showcase.)
This view of this room is also from a slightly different position than the final photograph above, but for illustration purposes, the conditions are exactly the same.
This is a very nice part of a lobby in a Caribbean resort hotel. It is a sunny, cheerful, relaxing place. Using a good camera on a tripod, knowing something about exposure, this is how this room has to be photographed just for the interior to be lit adequately. As you can see, to get this much light inside on a bright sunny day, the exterior gets completely overexposed and blown out, so severely that the overexposure causes severe flare and blooming into other interior architectural elements in the photograph.

It is quite deceiving how extreme a range of brightness there is between indoors and outdoors on a sunny day. Our eyes fool us into thinking that both the interior and exterior are similar brightness, and that this is how the scene will appear in a photograph. The above shot shows how this isn't true.

To illustrate this better, here is another photograph of the same space, but with the exposure set to record the outside lighting correctly:
(This is an example of a BAD photograph, in case you arrived in the middle of this discussion. I wouldn't want anyone to think this is my work that I'd like to showcase.)
Pretty gloomy. The exterior actually is still a bit too bright, but if I had adjusted the exposure down any further to fix this, the photography wouldn't show the interior at all.
The other problem with the first picture is the color. It is way too yellow, due to the incandescent lighting. This can be adjusted by a photographer familiar with architectural lighting, but the result is not too good either:
(This is an example of a BAD photograph, in case you arrived in the middle of this discussion. I wouldn't want anyone to think this is my work that I'd like to showcase.)
Now you see the weird mix of warm interior lighting mixing with the bluer light from outside. This is another trick our eyes play on us- we don't see the vast color difference between different types and sources of light. But a photograph captures this effect much more technically than our eyes see it.
A skilled Photoshop expert can work all kinds of tricks to try to overcome these issues. I'm pretty good at Photoshop, and here's my best result after a lot of work:
(This is an example of a BAD photograph, in case you arrived in the middle of this discussion. I wouldn't want anyone to think this is my work that I'd like to showcase.)
This is a good time to mention another trick we play on ourselves at times. Photography enthusiasts who are just starting to learn and love the magic of photography often suffer from this syndrome. I'll call it, let's see... the: "I spent so much time slaving over this picture in Photoshop, and I did things to it that my friends, family, and co-workers don't know how to do, and it's such an improvement over the original crummy photo, that it has to be good" syndrome, for lack of an elegant phrase.

I spent quite a bit of time and some pretty advanced techniques to achieve the above result, but the sad fact is that it is still a crummy photograph.

OK. Sick of looking at these crummy pictures? Here's what a professional architectural photographer who understands and can implement large lighting productions on location can achieve:
You get the idea. (This picture was actually taken in the same room facing the same direction, with the exact same conditions as the above examples. The composition was moved slightly from the above shots)
You can see that studio lighting equipment does a lot more than just brighten up a space, which is easy enough to accomplish just by using a longer shutter speed. What auxiliary flash (or strobe) equipment is allow the photographer precise control over the ratio of indoor to outdoor light, balance the contrast accurately, reproduce colors most accurately, and add a natural brilliance to a photograph that is often not achievable using existing light.
Many people say they like the look of photography shot only using natural light, and they don't like the harsh "strobe" or "flash" effect. This notion comes from looking at poorly done photography using a single on-camera flash or inadequate light modifiers. In these cases, the presence of the flash is obvious, where in the hands of a photographer who knows how to utilize an extensive location lighting system, the result is the natural looking effect as seen above.
Here's what was done here. Bail out if it gets too techno-nerdy and boring. The exterior brightness was reduced to a pleasing and natural level by increasing the camera shutter speed. Since flash (aka strobe) studio lighting is unaffected by camera shutter speed (below the camera's minimum flash synch speed, at least) we can then calculate how much flash power is required to bring the interior up to the exposure of the exterior for any lens aperture. For a room like this, it's a lot. Remember the brightness difference between interior and exterior in the available light photographs above? That should give you an example of how incredibly bright it is outdoors, and how much flash power we need to match the interior to it. By carefully balancing the ratios between ambient light and flash by calculating the correct flash power, aperture, and shutter speed combination, we can effectively make the interior as bright as we want independent of the exterior exposure.

For this photograph, I used five large studio strobe units. These are not like the little flash unit you might buy for your camera. These are big, heavy, metal studio strobes that pull a lot of 110 volt current. When they go off, they make a loud POP and actually vibrate a little. In other words, they put out a lot of power.

Two of these strobes were shooting through giant soft boxes to spread the light softly while still making it directional. The rest were use to fill in dark spots or to carve out a little contour or texture where needed.

This shot took about three hours for my assistant and me to set up, light, and shoot.