Key light - the primary light in an array of other lights that are used in a scene. The key light is very important and getting it in place sets the scene.
The Exposure Triangle - An aid to thinking about exposure
Refraction definition (optics) - Photokonnexion
Inverse square law :: Definition - Photokonnexion
Rembrandt Lighting Archives - Photokonnexion
What Is a Key Light - Setick
Key light in film: Everything to know – COLBOR
What is Backlight Photography — Lighting Techniques Explained
Refraction definition (optics) - Photokonnexion
What Is a Key Light? Our Complete Guide To Key Lights
What Is Key Light In Photography? - The Creativv
How to use a macro lens - Quora
What is Key Light? How to Use it For Better Photos & Videos