Unless you’re a trained cinematographer I suggest you check out – Directing Mood with Lighting Ratio & Dynamic Range before looking at the videos below. It will give you a foundation to more full appreciate what’s being shared.
Wescott – Pro Tip: Light Ratios – This Wescott video is geared to portrait photography, but it’s helpful.
Understanding Video Lighting and Contrast Ratios
The “Understanding Lighting and Contrast Ratios” video is a tad advanced. Dan get’s a little side tracked talking about kino-flo and hmi lights, and you might need an understanding of f-stop science to fully appreciate, but his info is accurate and worth a view.