Fair warning, this is really only half blog post and half personal rant. See, I'm a huge lover of Google Cardboard, virtual reality technology, and other immersive experiences. Sadly, I have to carefully research before I can partake in these, because I have photosensitive epilepsy. It rarely effects my life, until I enter a nightclub where I have to dance near the door (just in case), or have to cover my eyes quickly in a cinema. I'm far from the only one suffering from this condition. According to CureEpilepsy.org, 65 million people worldwide currently live with epilepsy, and each year over 200,000 people are diagnosed. About 5% of these have Photosensitive Epilepsy. Some users may not even know, if they've been fortunate enough to have never experienced a seizure. For example, in 1997 a Japanese cartoon aired a scene that included flashing colors, sending nearly 700 children into seizures, some of which had to be hospitalised for weeks.
We all like a good special effect, but the cheap trick of strobes and flashing lights are not worth it. As creatives, we need to be better than that. Even W3.org's Web Content Accessibility Guidelines has a section dedicated to avoiding patterns that are known to cause seizures.
So, how can you make sure your content is safe for us photosensitive folk? Here are some pointers:
Be sure that any flashing occurs at less than 3x per second. Most people with photosensitive epilepsy are sensitive to 16-25 Hz, but can be sensitive to rates as low as 3 Hz. Remember that what is safe and what makes a user comfortable are two different things. Anyone who has experience an epileptic seizure knows how scary and dangerous it can be. A user can’t be expected to measure the frequency of a “technically safe” flashing element. If they know they are sensitive to flashing, they’re more likely to just leave your content entirely if they feel any risk.
When possible, provide a way to “opt out” of flashing content. I've yet to experience any strobes or flashing content that was necessary to the experience, but at least a few times a year I have to leave rooms and turn off screens because of it. If you feel it is absolutely necessary to your project, allow users to opt out quickly, and in a way that makes them feel safe.
Reduce the contrast of necessary flashing content. Again, if flashing content is an absolute must, reduce the contrast. Stark lights/darks are much more likely to trigger a seizure than medium-level greys. Avoiding deeply saturated reds especially.