What is a paint sheen? The sheen is a measure of the reflected light from a paint finish. In other words, the glossier the paint (higher the sheen) the more light reflected off the surface. I learned a lesson in paint sheen last fall when I was painting our basement ceiling before we moved. I used a semi-gloss on the ceiling and because of the light bouncing off the ceiling + the dark paint, you could see every imperfection. To fix it I had to repaint the entire ceiling with flat paint to help diffuse the light and hide roller marks and brush strokes.