A sharp, white pinprick of light in a character's eyes seems to make all of the difference in 'separating the men from the boys', so to speak.
Never once in a Film Studies course, in a textbook, in a director's commentary or a book about making movies did I ever receive the advice to put lights in a character's eyes. The eyes are of the more reflective surfaces of the human body (because they're consistently moist) and therefore it does not take much to get those shiny orbs. However, if the on-set lighting plan does not include a small watt light pointed directly from the direction of the camera, the illumination becomes all too elusive. Creating this technique should be an essential part of a director/cinematographer's lighting plan when designing a shot.
A common Biblical quotation persists: eyes are the windows to the soul. Take it or leave it from a spiritual/metaphysical perspective but god damn if it isn't true enough of spectatorial identification between subject and viewer. Look at the frame grabs below from Inception (2010) and Barton Fink (1991) to get a visual example of what I am referring to.
Conversely, directors can choose to withhold the eye-light during moments when the audience should be denied that ability to read a character. John Ford put it to expert use in a moment from his seminal The Searchers (1953). In Ford's film, John Wayne plays Ethan Edwards; a pugilistic anti-hero, deeply flawed and racist. As events unfold and the narrative spirals into the darkest depths of human despair, Ethan appears perched to murder Debbie: the young girl stolen away by a tribe of savage Native Americans. This shift of a classically stalwart American hero, The Duke, is subversive and dark. The audience grows to fear Ethan and what his character is capable of. During this metamorphosis, at a pivotal moment in the film, Ford tracks in on Ethan's face making sure to keep the man's eyes enshrouded in darkness. The composition is gorgeous and economical. The darkness of the eyes reduces them to blackest pits. And sends shivers down my spine.
Now that I'm just about completed with my latest film, Fallout, I hope everyone finds our efforts at carrying this tradition of the eyelight into our humble little film. That said, ultimately, this is a technique that should remain entirely unconscious for the viewer. The spectator's identification with an on-screen character should not be a conscious suturing. So at the end of the day I guess I'm hoping that you do not notice the lights in the eyes...but that their effect elevates our narrative ten-fold.