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**: L<sub>dir<sub>i</sub></sub> - direction vector of light i
**: N - normal to the surface at the vertex
**: * [http://msdn.microsoft.com/en-us/library/bb172279%28v=VS.85%29.aspx Attenuation and Spotlight Factors]***: * Atten<sub>i</sub> - attenuation of light i***:: d<sub>i</sub> - distance from light i**:*:: d<sub>i</sub> = |L<sub>dir<sub>i</sub></sub>|**:*: a<sub>0</sub> - constant attenuation factor**:*: a<sub>1</sub> - linear attenuation factor**:*: a<sub>2</sub> - quadratic attenuation factor**:*: Atten<sub>i</sub> = 1/(a<sub>0</sub> + a<sub>1</sub> d<sub>i</sub> + a<sub>2</sub> d<sub>i</sub><sup>2</sup>)**:*: Atten<sub>i</sub> = [0, 1]**: ** Spot<sub>i</sub> - spot factor of light i**:*: Spot<sub>i</sub> = {[r<sub>i</sub> - cos(phi<sub>i</sub>/2)]/[cos(theta<sub>i</sub>/2) - cos(phi<sub>i</sub>/2)]}<sup>f<sub>i</sub></sup>**:*: r<sub>i</sub> - cosine of angle from axis of spotlight<sub>i</sub>**:*:: r<sub>i</sub> = norm(- light direction in camera space) . norm(L<sub>dir<sub>i</sub></sub>)**:*: phi<sub>i</sub> - penumbra (exterior cone) angle of spotlight<sub>i</sub>**:*: theta<sub>i</sub> - umbra (interior cone) angle of spotlight<sub>i</sub>**:*: f<sub>i</sub> - falloff factor of spotlight<sub>i</sub>
** [http://en.wikipedia.org/wiki/Blinn%E2%80%93Phong_shading_model Blinn-Phong and Phong]
**: V - viewpoint vector