You can easily google what causes photosensitive seizures. Go for it. There are known rates of flash that typically can cause seizures, and they generally also have to be very bright and fill the field of vision, which for the most part will rule out bike lights. You may also want to try and find a single account of this kind of light causing one. There are lots of blog posts and such about it, but I have never seen one with any real, solid facts or a study, or even an author saying "this happened to me". There is no need for you to spread FUD about this when you have no information that it's even a problem.