What a ring light actually does
A ring light surrounds the lens, so the light comes from every direction around the camera at once. That fills in shadows almost completely and leaves a distinctive circular reflection in the eyes — the catchlight, which is the look people are usually after.
The dark centre is not decoration. It is what lets you put a camera, or a preview window, in the middle without the light source being directly behind it. On a screen, that means you can watch yourself in the hole.
- Close-up video where you want even, shadowless light
- Anything where the circular catchlight is the look you want
- A light that leaves room for a preview window in the middle
Using a screen as a ring light
Put the screen directly behind or beside your camera, as close as you can, and turn its brightness up. The closer it is, the more the ring behaves like a real one — light falls off quickly with distance, and a ring three feet away is just a dim rectangle.
The edge of the ring is deliberately soft. A hard-edged bright shape reflects in glasses as a visible rectangle; a soft one is much less obvious.
Adjusting it
Set the temperature to match your room, and drop the brightness if the light is too harsh — a screen at maximum brightness close to a face is genuinely quite bright.
If you want more output and do not need the catchlight, switch the shape to the whole screen. Area beats shape for raw brightness every time.