Constant or continuous studio lighting has undergone a comeback as well as an overhaul. Constant lighting is just that – studio lighting that stays on all the time (as opposed to strobes or speedlights that emit a bright burst of light when triggered). As with all things, there are some advantages and disadvantages to using constant lighting.
The color temperature of the light produced by constant lighting has improved over the last few years and emits a more daylight balanced light. Also, with constant lighting, what you see is what you get. Because the lights are on all the time, you can position your model and fiddle with the light stand to have the light fall precisely the way you want it. You can instantly see where the shadows fall, adjust the highlights and/or double check that the catch lights hit the eye just by raising or lowering the light or moving the stand around. Constant lighting = instant gratification!
Constant lighting also takes out the guess work. What you see in the camera will be your final image. You can use your built-in light meter to get the correct exposure while you might need to use a handheld light meter if you use strobes. And you won’t need a cable or remote trigger to fire off constant lighting as you would with strobes. These advantages mean that you can get set up and start producing images faster. Because a lot of the trial and error is eliminated, you will have a shorter learning curve for studio work.
Obviously if you are shooting video with your DSLR, constant light is your only option.
But with the light always on, constant lighting can make for an uncomfortable situation for your model. Older lights can get hot, which is especially bad with food photography. Not only will your model wilt under the heat but that bowl of ice cream doesn't stand a chance! Fortunately newer LED lights, fluorescent lights, HMI (Halide Metal Oxide) or even tungsten lights use less electricity and give off much less heat than the older lights.
Though constant lights have come down in price and are generally less expensive than strobes, they are not nearly as powerful. Strobes can overpower any ambient light in the studio while constant lights don't have nearly the same ability to overpower unwanted ambient light. Strobes or speedlights pack a large punch of light in a small burst, but constant lights don't have anywhere near the same intensity.
Because constant lighting is not as powerful as strobes, getting a correct exposure will require you to open up the aperture to something like f/4.0 or increase the ISO to compensate for the lack of light. If you are shooting a sitting model or doing product photography, the lack of depth of field shouldn't cause much of a problem. But if you are photographing an athlete jumping in the air in your studio and you want to freeze the action to prevent blurring, you will run into some issues. Strobes or speedlights give you more flexibility and options. If you want to go for a specific look in your shoot, be sure to check out what modifiers are available for constant lights as sometimes your options of light modifiers are limited.