With this system, the light remains on and at a constant intensity or brightness. Great for getting instant feedback about the highlights and shadows on your subject, continuous lights are also relatively cheap compared to strobe-lighting systems. In video production, they’re used 99% of the time.
Unfortunately, they’re nicknamed “hot lights” for a reason. They get extremely hot because of their tungsten or quartz-halogen bulbs. At 500+ watts each, these lights require special, heatproof accessories for safe use in your studio or home. Tungsten hot lights, can increase the ambient temperature quite considerably, just three 1000-watt units will not only suck lots of juice, but can also wilt or even melt certain props used during a product photography session. For example, prop wax with prolonged heat exposure will no longer hold properly, and if you’ve concocted an elaborate scene, it can be a frustrating event when it all collapses.
Newer lights are on the market today, which use fluorescent bulbs that don’t generate the same heat. The trouble is that you’ll need many fluorescent bulbs to match the intensity of a tungsten bulb.
The second problem with hot lights is the lack of light-intensity control. Most continuous-lighting sources have only one setting for brightness or perhaps a simple toggle with half or full power. To top that off, most lights aren’t strong enough to freeze action at the lowest ISO settings, unless you shoot at relatively large apertures in the f2.8 to f5.6 range. As a studio photographer, lighting is your paintbrush – you need maximum freedom to adjust the lighting conditions in your “controlled environment.” Unless you are on a tight budget, I don’t recommend this route.
These lights are small, very portable units that attach to the camera’s hot-shoe connector. They’re rarely used in studio photography because they don’t provide any visual guide for shadow and highlight placement, which basically means that you’re working blind, more or less by trial and error. Some photographers use flashguns in the studio for high-speed, action-freezing situations, such as capturing liquid splashing (some studio strobes are able to do this as well). They’re most often used outdoors for weddings, reportage, and wildlife or nature photography.