Jean-Pierre Dreyfus, Canada
Keep in mind the basic physics of how light operates. If the light source isn’t immediately in front of the window (say, the sun), you’ll barely notice any distortion in the parallels of the light beams. On a surface that’s perpendicular to the blinds, the light and shadows will follow the direction of the light, much like on the back wall in this illustration. On surfaces that are parallel with the window, the light and shadows will also be parallel as they fall across the character’s face and body.
Remember that the light will follow any changes of the surfaces and that’s exactly why you can use it to describe form. You can also suggest the variation of materials by carefully addressing the edges of the lights. Here I’ve blurred the light shafts that appear behind the character on the smoke in the room.
I first paint the character with a generic light source coming from the upper left of the scene, and then darken her whole body to suggest that she’s in complete shadow. Then I paint the light shafts on a separate Color Dodge layer and distort each one to match the affected surfaces, erasing back all the areas that aren’t facing the window. This gives me a solid base for the lighting in the room, which I only have to fine-tune during the detailing phase.