This is a combination of two techniques you can use to find good light if my model isn’t available and I don’t have a stand in.
I simply hold a marble in my fist and hold it at eye level in the spot I’m thinking of photographing my model. The catch lights will be reflected in the marble and I can see the quality of light on my skin tone.
Great portrait lighting is soft and fills in all the wrinkles of my fist with nice catch lights visible.
Caca light is dull and there are no catch lights visible