Title Requirements and Parameter Settings of a Speckle Contrast Measurement System

Laser speckle contrast Cs is a key metric for evaluating image quality in laser displays. The geometry and parameter settings of a speckle measurement system can significantly affect the measurement results. The current international standard IEC 62906-5-2:2016 and the Laser Illuminated Projector Association recommendation LIPA RP v1.0 differ in their parameter requirements, limiting the comparability of measurement results. Considering the practical operating luminance range of projection systems, 50–1000 cd/m2, and the approximately 1′ spatial resolution limit of the human eye, this study recommends the following principal parameters: an F/5.6 aperture corresponding to a human pupil diameter of 3.13–2.40 mm, an effective pixel size of 4.8 μm corresponding to the approximately 4.9 μm spatial integration scale of the human retina, and an exposure time of 50–200 ms. Measurements show that speckle contrast increases with F-number, rising by approximately 198% from F/2.8 to F/22, and decreases with increasing binning, screen tilt, and defocus. These trends agree with the spatial integration model Cs=C0⋅r/1+r2. Exposure time is not used as a parameter for matching human vision; instead, it is constrained by the requirements to avoid overexposure and maintain an adequate signal-to-noise ratio. An exposure time of 100 ms is recommended, and the actual value should be reported. Screen tilt should be avoided, and the system should preferably provide focusing assistance.