“Light is used to reveal shape(silhouettes), form(highlight, shadow and contrast between the two), texture, colour(convey emotions), emotion(convey feeling).”
The internet is full of how to use artificial light in studio and I have done few shots in natural light and with external flash. They are not as the exercise required but the photographs helped me to understand a little bit of the artificial light.
The difference between the first two pictures is the color of the coat which puts the subject face into different light . I put the flash to hit the ceiling and set it according to the lighting from the room. (1/4 or 1/8) The third photograph is on the balcony where was plenty of light and I didn’t need flash and the lit is coming from the left and from back which makes the face to be in light.
The last photograph shows the subject face extremely lit by flash that reflects in the back window and all the light falls on the face and contrasting with natural light in a weird manner.