Special Relativity (SR) is the cornerstone for modern physics and
variety of applications. SR is based on two postulates, the principle of
relativity (the first postulate) and the principle of constancy of speed
of light (the second postulate). Recently we have (1) shown that the
light propagate as particles/photons in the “pure” wave experiments,
such as double slit and grating experiments; (2) proposed experiments to
measure the speed of the photons by an observer moving relative to the
source and thus, to test the second postulate for photons. In this
article we propose a classroom experiment to test the second postulate.
If the experiments show the existence of interference pattern (the
negative result), the constancy of the speed of the photons holds,
namely the second postulate of SR is experimentally confirmed. If the
experiments show no interference pattern (positive result), then the
propagation speed of photons is not constant, namely, the second
postulate of SR is disproved. Either negative result or positive results
would be profoundly significant.