HID sources include mercury vapor, metal halide, high pressure sodium and low pressure sodium. HID is also a point source, which provides the opportunity for better light control. Specular Reflectors Specular reflectors may also be used for classroom applications. Specularity is the measure of a surface's ability to reflect all of the light at the inverse of the angle at which it is received. The opposite of specular is diffuse.
White paint is diffuse.
When light hits white paint, it scatters in many directions because white paint is only 6 percent specular. Very little control can be exerted when a white painted surface is used as a reflector. Many schools are being retrofit with an industrial channel with a painted baffle under the lamps. Essentially, there is no light control. All of the light is dumped under the fixture.