How can I achieve the Rembrandt lighting effect in a portrait?

To achieve the Rembrandt lighting effect in a portrait, position the light source at a 45-degree angle to the subject's face, slightly above eye level. This will create a triangle of light on the cheek opposite the light source, with a small shadow under the eye on the other side. Adjust the distance and intensity of the light to control the contrast and shadows for a classic Rembrandt look.