The specular exponent defines how sharply the intensity of reflected light falls off away from the mirror-reflection direction. Higher values lead to more sharply defined reflections, typical of shinier materials. Values above 10 produce definite "specular highlights".
The usual approximation in computer graphics takes the intensity of light at an angle from the mirror-reflection direction to be . Although not particularly accurate from a physical point of view, this approximation is perceptually quite satisfactory for many simulated materials.