STROBE VS. CONTINUOUS LIGHTThe first decision you need to make is whether you want to use strobes or continuous lights. One factor that may affect this decision is whether or not you plan to shoot video with your lights, too. If so, you may prefer constant lights, because strobes don't work with video. If you're solely shooting stills, though, then I might suggest you keep strobes in the running, because the ratio of cost to output is fairly favorable, and you have a whole array of modifiers and accessories specifically built for strobes of all shapes and sizes.
HOT-SHOE STROBESThe most affordable strobe option is the compact and portable hot-shoe mounted variety. Also known as a speedlight flash, these small strobes can be had for just a few hundred dollars, and many offer TTL communication with cameras for auto-exposure functionality that can even control the light. Better still, many hot-shoe strobes communicate with one another, making it easier to get into multiple-source lighting. And last but not least, there's an ever-growing movement toward lighting with speedlights because not only are they affordable and compact, but their relatively lower power output also makes them easier to balance with ambient light even at low levels. And that growing popularity also means there are tons of options in modifiers—like snoots, grids and softboxes—that used to require you to work with studio-style strobe systems
STUDIO PACK AND HEAD SYSTEMThe traditional studio strobe system consists of a power pack (really a big ol' capacitor) that plugs into a normal A/C wall outlet and then sends power via tethered cables to a number (often four, six, or even more) of satellite heads. Makers such as Dynalite, Speedotron, ProFoto, Elinchrom, Norman, Hensel, Bowens and Broncolor offer pack-and-head systems, which are popular with studio photographers who have easy access to electricity as well as the space to accommodate the fairly heavy and bulky—but often quite powerful—systems. These systems tend to be fairly heavy duty, and modular so you can add additional lights piece by piece as you grow your setup. The biggest benefits are the high outputs that are available (often as much as 2400 or even 4800 watt seconds—the measure of strobe output), which surpass any other type of flash system, and relatively low per-watt-second cost. A world of high-quality modifiers are available for studio pack-and-head systems, too—just as they are for monolights.
MONOLIGHT STROBESThe alternative to the pack-and-head strobe system that still provides fairly high output is the monolight, or monobloc. The telltale sign you're dealing with a monolight is that it has the relative look and feel of a large studio pack-and-head system, without the pack. That means that the capacitors and circuit boards are all self-contained in each head, along with a triggering connection and usually a photo cell sensor too. That makes monolights relatively smaller and more portable than a pack-and-head system—which makes them ideal for taking on location. The biggest difference between pack-and-head strobes and monolights is that a pack system only requires one electrical outlet, while monolights require electrical power for every individual light. The benefit, though, is that you're not tied to a particular system, and you can augment one brand's monolight with another at a later date. Popular makers include Paul C. Buff, Photogenic and many other makers of pack-and-head systems as well.
TUNGSTEN HOT LIGHTSWhen it comes to shooting still photos and video, the ideal solution is a do-it-all continuous lighting source. And in terms of straight up continuous light output, the biggest bang for your buck comes from tungsten hot lights—so named because they heat up fast. When working with hot lights, work gloves are essential—as is keeping flammable modifiers far from the source. Tungsten balanced bulbs are most common in hot lights, and they match the warm output familiar in traditional incandescent light bulbs—measured at about 3200 degrees on the Kelvin color temperature scale. Strobes and daylights are much cooler—both literally in terms of temperature and figuratively in terms of color temperature, measuring in the 5000+ range. In order to match tungsten lights with daylight ambience, blue gels are necessary to "cool" the color temperature of the light. (The reverse also holds true; orange gels will warm daylight and strobe light to match tungsten hot lights and traditional incandescent bulbs.) Some hot lights use daylight balanced bulbs for balancing with daylight ambience, and some even come with a battery ballast allowing them to be useful outdoors where daylight is abundant but electrical connections are not. While the heat and relative bulk of tungsten hot lights require a bit of getting used to, the relatively low cost for high output is hard to beat in continuous sources. These lights were the industry standard in motion picture and television production for generations—and they also helped define the look of classic Hollywood portrait lighting. Many hot lights include built-in Fresnel lenses, which allow the light to be focused into a spot, or spread broadly for greater coverage. Popular makers include Arri, Mole-Richardson and Smith-Victor.
FLUORESCENT CONTINUOUS LIGHTSIn an effort to develop constant lights that remain cool to the touch while still outputting bright light, manufacturers first turned to fluorescent tubes—such as those found in the popular Kino Flo variety of fluorescent lights. Because the sources aren't small like individual tungsten bulbs, these lights are inherently broader and softer than an unmodified hot light typically is. And because the color of the light output is based entirely on the variety of fluorescent tubes used in the fixture, color temperature can be changed from tungsten to daylight simply by swapping the tubes. A more recent variation on fluorescent constant lighting is the innovation of CFL fixtures—designed to work with the same type of compact fluorescent light bulbs that are used in traditional home applications. Some of these fixtures are designed for a single bulb, while others can accommodate several in order to increase the output. Best of all, CFL fixtures are perhaps the most affordable, and one of the most cost effective, light source available. The downside, though, is relatively low output. Interfit offers a wide variety of CFL fixtures.
LED CONTINUOUS LIGHTSThe most recent innovation in lighting is the Light-Emitting Diode. The technology has been around for decades, but only recently have manufacturers been able to produce LEDs with high enough output for traditional photographic and motion picture production needs. These lights are arrayed into grids, from a few inches in size (often mountable to a camera's hot shoe) to as much as 1x1-foot or even 1x2'-feet at the large end. They are thin, which makes them extremely compact (perfect for users who value portability), really inexpensive to run (because of their low power consumption) and very versatile. The best varieties are not only dimmable but color changeable—meaning you can dial in precise white balance from tungsten to daylight or anywhere in between. Much like fluorescent tube lights, the sources are not pinpoint so the lights are inherently softer than bulb-based sources. The downsides of these amazing lights are twofold. First, they tend to be quite expensive at the high output level and that's required for serious users, and two, although the lights are bright, they aren't able to "throw" that illumination over long distances. Photographers who want to illuminate a large space, for instance, may find other sources preferable.
In the end, while many of these lighting options are versatile enough to do double-duty for handling different photo and video needs, you may find that it's harder to find one light that does all things well, and instead use different sources for different purposes. This is the approach that we take in my studio, and while it's certainly not the most affordable way to go, it means we can always choose the ideal light for a given situation.