As their name indicates wall washers and wall grazers both serve to direct light at a wall in order to make a space seem larger and brighter. They draw the attention to the smooth vertical surface of the wall. Wall washers and wall grazers actually serve different functions.
Wall Washers: A wall washer does what the name implies; it washes a whole wall with light. Because of the angle of the light a wall washes minimizes imperfections, dent, bumps and texture to create an even, smooth wall surface from floor to ceiling. The angle of the light eliminates any shadows that might be cast by imperfections.
Wall Grazers: Wall grazers, on the other hand, actually serves to emphasize, "graze" or accentuate texture on the wall. Again, because of the angle of the light, texture is highlighted and the shadow of the texture becomes a part of the beauty of the wall.It is typically used on stone or brick surfaces.
Both wall washers and wall grazers are traditionally mounted on or recessed into the ceiling. They can also be mounted to the floor and directed up at the wall.