Answer:
Explained
Step-by-step explanation:
Michelson contrast is used for patterns where the distribution of bright and dark segments is nearly equal.
It is given by:

where I_max = maximum illumination and I_min = minimum illumination
we know that
typically, I_min = 54% of I_max (general standard)
or I_min = 0.54 I_max
putting this value in above equation to get m
this approximately corresponds to m = 0.3 or 30%
hence, 30% recommended as the minimum Michelson contrast