The ring light is a useful tool for photographers that goes back many years and has been especially useful in scientific and extreme close-up work where the physical camera and lens makes other types of lighting difficult. Both strobe and constant-on versions for video are available. But ring lights are very useful for many photographic situations because they provide what the camera sees as a perfectly shadowless fill light. Many videographers use small lights that mount above the lens to help fill shadows and boost overall illumination in dark situations, but these lights do cast ugly little shadows under the nose, chin, and so forth.
For a few hundred dollars you can buy LED Ring Lights that are large enough for a typical still camera or small video camera with the sun shade removed. I wanted one that would allow for the sun shade to remain in place on one of our Sony HD cameras, an HVR-Z7U. I figured one this size would work with almost any video camera. (The Z7 was on location the day this picture was taken -- the camera shown is an older SD Sony)