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**https://www.opengl.org/sdk/docs/man2/xhtml/glLight.xml**
GL_SPOT_EXPONENT

params is a single integer or floating-point value that specifies

the intensity distribution of the light.

Integer and floating-point values are mapped directly.

Only values in the range 0-128 are accepted.

Effective light intensity is attenuated by the cosine of the angle between

the direction of the light and the direction from the light to the vertex

being lighted, raised to the power of the spot exponent.

Thus, higher spot exponents result in a more focused light source,

regardless of the spot cutoff angle (see GL_SPOT_CUTOFF, next paragraph).

The initial spot exponent is 0, resulting in uniform light distribution.

GL_SPOT_CUTOFF

params is a single integer or floating-point value that specifies

the maximum spread angle of a light source.

Integer and floating-point values are mapped directly.

Only values in the range 0-90 and the special value 180 are accepted.

If the angle between the direction of the light and the direction from the

light to the vertex being lighted is greater than the spot cutoff angle,

the light is completely masked.

Otherwise, its intensity is controlled by the spot exponent and the

attenuation factors. The initial spot cutoff is 180, resulting in uniform light distribution.