It should be noted that a Lambertian surface is merely a useful fiction. No real surfaces behave precisely according to lambert's cosine law, but will exhibit some degree of specularity. Porous, matte objects such as a paper towel or a thick plush carpet, approximate a Lambertian surface most closely. To simplify calculations of lighting characteristics in a room, it is sometimes assumed that all surfaces are Lambertian. In lighting, one must distinguish carefully between the meanings of the two.
Reflection is the process whereby an object reradiates incident luminous energy.
When this occurs we say that light is reflected . Reflectance , however, is the measured or calculated ratio of reflected flux to incident flux. Unless otherwise specified, it is assumed that reflected flux refers to all flux emitted into the hemisphere surrounding the surface normal vector. This is known as hemispherical reflectance. For such surfaces there is potentially a different amount of flux reflected at each angle throughout the hemisphere.