Life is interesting sometimes. Not long ago, I was writing a tip in The Accessible Web about flicker and photosensitive epilepsy. I kind of went back and forth about whether this was a common enough issue to worry about. In the end, I decided that it was too important to not discuss in depth.

When video flickers at the right speed, some people have seizures. The degree of the seizure varies, but to be sure, this isn’t a pleasant way to relax watching television or a web video. If you test your video for flicker problems using Harding FPA or TRACE Center’s PEAT tool you can avoid inappropriate levels of flicker. If you don’t test it, you run the risk of seriously harming some of your users.

This was exactly what happened this week when a video introduction was rolled out for the 2012 London Olympics. A segment in this video featured a multicolor flicker that was not tested for problems and viewers suffered from seizures. Fortunately, it appears that fewer than a dozen people reported being affected by this video (An infamous episode of Pokemon a few years back had over 500 reported seizures). I’m not as concerned about the reported numbers as by the potential damage though—in the end, 23000 people in the UK were put at risk of seizures caused by this video.

Most of us don’t worry about things like the flicker rate of our content very often. It seems like a minor factor that effects only a few people. It’s never just a few people - a small percentage of the total population is still in the thousands. It’s also not a great way to do business. London mayor Ken Livingstone had these comments:

• If you employ someone to design a logo for you and they haven’t done a basic health check you have to ask what they do for their money.
• Who would go into a firm like that again and ask them to do that work. This is a pretty basic thing.

These are important things to think about. As web designers, we make our livings by serving an audience. If we allow harm to come to that audience, we allow harm to come to ourselves.