Chapter 9 305 rather than calculating the diffuse reflection separately it is more facile to determine the specular and diffuse (S + D) together.13 Alternatively, the goniophotometer may be equipped with polarizers allowing for the generation of separate specular and diffuse reflection curves utilizing parallel and crossed polarizers, respectively. The polarizers are placed in front of the illuminating Figure 4. Typical curve obtained from goniophotometric experiments containing both specular and diffuse components (S+D) and extraction of the specular (S) portion of the curve using mathematical software. Reprinted with permission from Keis et al.13 Figure 3. Rudimentary diagram of a goniophotometer experiment. A hair fiber is held taut and struck by incident light at angle, i. Scattered light is then detected by rotating a photomultiplier tube from 0 to 90 degrees with respect to the perpendicular to the fiber. Two of the photomultiplier positions are shown. Reproduced with permission from Reich and Robbins.20