I've seen several references to a loop lighting pattern, often in the context of portraiture lighting.
What is meant by the term?
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image (c) portraitlighting.net
It's where you have the lightsource above and slightly behind the subject so the light runs down the nose and creates a loop shaped shadow.
Personally I don't like the shadow, I either go for something more dramatic and join the nose shadow to the unlit side leaving just a triangle highlight on cheek or go for a broad lighting setup if I want a flattering well lit scheme.