*4.2.2 Speckle*

The laser light is highly coherent and thus can induce speckles. In LD-based white light, speckles are inherent due to the residual pump source, which degrades the contrast and visual definition. Luminaires that use powder phosphor exhibit less speckles than single crystal phosphor because multiple light scatterings occur in powder phosphor, destroying the optical coherence. Hence, powdered phosphorbased light exhibits little speckles. The speckles can be reduced by using a rotating diffuser and light-diffusing membranes.
