For those people who suffer from epilepsy, flashing lights of any kind can constitute a threat. Somehow, repeated flashing (as often occurs at discos etc) can trigger an attack, leading to embarrassment, discomfort and possible injury.
Computer screens flickering at 50Hz or less or stuttering fluorescent tubes are particularly prone to provoking fits and the point with these is that, unlike the roller disco example, people are often exposed to these effects for some time without noticing them -then a serious attack may ensue.
Today’s invention is a tiny light sensor and associated electronics which can be worn discreetly by epiletics (especially young people who may be additionally distracted). This would constantly monitor the scene ahead for signs of sustained flickering and provide an unobtrusive buzzing alert, so that the wearer could retreat before succumbing.