The inverse square law can help a cinematographer have precise control over the contrast ratio of their shot.
Read this article until "The Light Meter"
High Key Lighting
High key Lighting is Low contrast
Meaning the ratio between highlight and shadow is low, so 1:1 would be no contrast and 1:2-1:3 would be a little more, but still within the realm of high key. High-Key lighting is common in comedies, romantic comedies, variety shows, and sit-coms. One of the reasons for this is that a lower contrast situation allows physical comedians to move freely about the set.
- Used in a lot for situation comedies because it allows for physical comedy, because actors can move freely around a set without stepping out of the light
- It also conveys a happier and lighter mood
Below find a scene from Friends where the characters have to move to different locations in the scene. The lighting is high-key, but not flat, and has little enough contrast so that the characters can move around without stepping into shadow. If this scene were lit like a film noir, then the subjects would step into dark shadows while walking around. There's nothing wrong with lighting a dark scene that way, but in the scene below, you would miss out on valuable information.
Often, high-lighting is used in romantic comedies as well to set a lighter tone.
When you think of a cloudy day, you probably imagine a somber tone. In terms of lighting however, the contrast ratio found on a cloudy day is very similar to what you see above.
Light diffused through the clouds is similar to soft lights, umbrellas, and silks that create soft light.
Usually flat lighting (1:1 ratio) isn't used in professional shoots, but will likely be 2:1 or 3:1. The images created with high-key lighting aren't always low contrast either. The contrast in a high-key scene is usually created by art direction.
Look at the shot above from the original Will and Grace. The lighting is high-key with something like a 2:1 ratio, but there is a lot of contrast in the shot. Why is that?
Imagine the shot in black and white. Can you find something in the image that is 0%-10% white? The paper they are holding? The pages of the book?
Can you find something that is 90-100% black? the black pillow? the picture frame? Grace's jacket? Will's pants? There is contrast in the shot, but it is created with art direction--objects placed within the frame. Pretty much every shade on that grayscale is represented with the help of art direction.