Feathering a light source is one of the most fundamental techniques any photographer working with artificial light should know, as it is highly useful and versatile. This excellent video will show you how to use feathering to create better lighting for your portraiture work.
Coming to you from Gavin Hoey with Adorama TV, this fantastic video will show you how to use feathering for controlling the light in a portrait. While using a range of different modifiers can alter your light, feathering simply requires changing its angle relative to your subject. Put simply, feathering is the process of angling a light so that it only strikes the subject and the rest of the scene in a desired area instead of spilling all over the entire scene. The effect is somewhat similar to what you will get from a grid, but grids can be especially pricey depending on the size of the modifier, or they might not even be available for the one you are using. Check out the video above for the full rundown.
And if you would like to continue learning about lighting, be sure to check out "Illuminating The Face: Lighting for Headshots and Portraits With Peter Hurley!"
I like to envision how the photons are bouncing all around and how they're hitting the subject. But maybe that's just me.
Ditto more adding bounce with some feathering..