Continuous Cold Lights
Fluorescent and LED lights have exploded in popularity alongside HDSLRs and the emergence of hybrid photography. Compact LEDs allow you to have extremely lightweight, battery-powered lights, and along with fluorescents, they give you easy color control, as well.
A decade ago, there wouldn't have been much to write about continuous cool lights for photography, but the technology has boomed in recent years, partly because HDSLRs have turned many photographers into cinematographers, too. Improvements in sensor signal-to-noise ratios mean higher ISOs can be used, so less light is needed. Compared to hot lights, continuous cool lights—in the form of fluorescent tubes or light-emitting diodes (LEDs)—don't deliver as much pure lighting power, but they're considerably more compact, more energy-efficient and don't get hot. They must also overcome the dreaded "green spike" that can cause sickly color shifts, though the best LED and fluorescent fixtures have largely eliminated the problem. They're incredibly convenient light sources, but if sun-caliber power is what you need, other options probably will work better than LEDs and fluorescents.
Cool & EfficientUnlike hot lights, continuous cool lights don't give off much heat—at least not in the direction of the scene you're photographing. This makes them safer and more comfortable since you can place them close to subjects and touch them without gloves.
In their most affordable form, fluorescent continuous lights use Edison base screw-in bulbs, albeit larger, higher-wattage versions than standard household CFLs. To increase output, many of these fixtures have multiple sockets—two, four, six, even as many as nine lamps fit in a single fixture that increases the amount of light. The bulbs are fairly inexpensive, available in a variety of color temperatures, and can be mixed and matched to subtly warm or cool the fixture's output.
Beware Of FlickerPro-caliber fluorescent lights use biaxial (or biax) tubes and external ballasts to produce more consistent color temperatures and flicker-free output crucial for video. When dimmed, fluorescents are more likely to flicker, not a big problem with stills, but a huge problem for video. Technically, all light sources flicker, but the flicker is most pronounced with fluorescents. In addition to being brighter, the best of these lights are also considerably more expensive.
Because of their lower power consumption, continuous cool lights are less expensive to operate, and their bulbs last a very long time. With the compact size and ultra-low power needs of LEDs, they can easily run on batteries, so they're extremely useful for remote locations where access to electricity is scarce.