During WWII, flashing lights were used as a tactic to combat night bombers as I recall....also quite familiar with the problem from my Chinook days in the US Army and again with the S-58T....nothing to do with epilsepsy as I recall. The worst I ever got was a feeling of discomfort....or uneasiness....the Chinook was worse when the flicker reflected off the Attitude Indicator...with a sun angle from slightly behind the aircraft...usually shortly after lunch.