Here’s why you should always keep the brightest light behind you when shooting video:
Modern video cameras, from cell phones to HD, adjust automatically for light. If the light’s too bright, they close down the lens to let less in.
Normally, no problem for you or the video camera. Your outdoor shots in bright light look great, and so do your indoor shots by candlelight.
Unfortunately that smart circuitry gets confused when it has to deal with multiple light levels in the same shot. Most video camera circuitry is set to expose for the biggest, brightest thing in the frame. Your camera only has one lens—if it closes that lens to make the brightest things in the frame look normal, the darker things in the frame go super dark. If you put your grandmother in front of a window at 2 p.m., the camera will expose perfectly for the apartment building across the street and Grandma will be a black cutout silhouette.
To prevent her from looking like a refugee from the witness protection program, keep the brightest light behind you. That way it will fall on your subject, and they’ll be the brightest thing in the frame. And we’ll be able to see them.
If you’re outside in the daytime and your subjects are squinting, try moving so that the sun is still behind you, but not RIGHT behind you. That way the light will hit them at an angle instead of straight on.