Key light - Wikipedia

Calvin cycle - Wikipedia

Key light - Wikipedia

File:Low-key photography - portrait of a young man.jpg - Wikipedia

Lighting - Wikipedia

Light - Wikipedia

Egmont Key Light - Wikipedia

sky's light-n-shading thingie, Wiki

I think might be the key. and why these interact at all, with particles containing mass

Callier effect - Wikiwand

Three-point lighting - Wikipedia

Fresnel lantern - Wikipedia