Abstract: An apparatus for sensing blend segregation in a mixture comprises a light transmissive window disposed within a feed connection between a hopper and an extruder for example, a light source for emitting a light beam, and a light sensor to perform spectrum analysis of any incident light supplied thereto. An illumination assembly has a first end optically coupled to the light source and a second end optically coupled to the light transmissive window to illuminate a portion of the internal path provided by the feed connection. At least one detection assembly is provided, having a first end disposed adjacent to the light transmissive window so as to detect the reflection from any illuminated polymer blend passing therethrough. The light sensor collects the diffuse reflecting light from the polymer blend and transforms the diffuse reflecting light into tri-color signals, reflection curves or the like, for comparison with other diffuse reflecting light so as to determine if a particular blend is segregating.