The statistics of temporal integration of dynamically scattered light is commonly employed to calculate the correlation time of the light and related physical properties of the object that produce it, i.e. scatterer’s speed. Recently, studying the statistics of time-averaged fluorescence intensity, it was reported that a small dead-time (1% of the exposure time) of the photo-detector increases the correlation time by one order of magnitude compared with an ideal photo-detector. Applying the same theory to the speckle contrast calculation for blood flow measurement, we found that the effect of dead-time is negligible compared to an ideal photo-detector for contrast calculation. All Rights Reserved © 2015 Universidad Nacional Autónoma de México, Centro de Ciencias Aplicadas y Desarrollo Tecnológico. This is an open access item distributed under the Creative Commons CC License BY-NC-ND 4.0.