Some viewers with photosensitive epilepsy are sensitive to flashing lights and certain repetitive visual patterns, many of whom don't even know they have this sensitivity.
All programmes should comply with Ofcom's guidelines in relation to the requirement to maintain a low level of risk to viewers who have photosensitive epilepsy. Programmes that do not comply are likely to fail their technical review and sequences may have to be altered or removed. The guidelines can be found on Ofcom's website, annexed to the guidance notes accompanying Section 2 of the Code.
As a very basic guide, if a sequence of flashes occurs more than 3 times per second and covers more than a quarter of the screen, it is likely to be problematic.
On occasions the Code anticipates that it may not be reasonably practicable to follow this guidance and where that is the case and where broadcasters can demonstrate that the broadcasting of such flashing lights and/or patterns is editorially justified, alerting viewers in advance will suffice - for example flash photography in a live or fast turnaround news item at a film premiere or some other similar event. The warning should be given verbally and also if appropriate in text at the start of the programme or particular item. Before this is done, producers should always seek the advice and consent of their commissioning editor.