From the Tank Museum:
Mark II A12, Matilda Canal Defence Light (CDL)
Night fighting always presents problems but searchlights had been tested on tanks as early as 1919. The idea of turning them into an offensive weapon is credited to a Mr A V M Mitzakis, who devised his scheme before the war but the British authorities did not take it up until about 1940. The idea was to use a light of such power that it would dazzle the opposition, leaving them temporarily blind and disorientated.
Five British and two American battalions were trained on CDL and two of the British units went out to Egypt. In fact the CDL was never employed as intended. A few tanks were used to cover the Rhine Crossing and there were incidents in India after the war but that is all.