This mostly happens when one loads presets.
L is the size of the grey-scale viewing area, in meters.
Max 200x200, unless you resize the window. Integration points huygens approximates the wide slits as a set of several thin slits, with carefully chosen separations and weights. Wide slits will look like several point sources if this variable is too small. This defines what amplitude is given the darkest and lightest value for the grey-scale plot. Defaults to grey-scale.