Shaun Shue

How to: Flash lights and accommodate people with photosensitive epilepsy

I read about Liana Ruppert having a seizure, triggered while playing Cyberpunk 2077 for review. CD Projekt Red was quick to add a warning and a fix, but there are good practices to minimize risk in the design phase. There wasn’t a clear guide when I needed one, so I’m making this: For anyone flashing lights for effects, grabbing attention, or any other reason—in person or on screen—here is what the Epilepsy Foundation and IEEE lay out:

For screens, aim to meet the British Independent Television Commission (ITC) guidelines1 at a minimum:

1. Use fewer than 3 pulses per second (Hz)

2. Flashes should affect less than 25% of the screen

Assuming the initial version Liana played is similar to this IGN preview4, the flashing effect can cover most of the screen, and I counted ~11 Hz.

Cyberpunk 2077 flashing lights

Multiple factors contribute to and compound the risk2,3. Though flash rate (#1) and visual field (#2) are the papers’ most mentioned considerations, if meeting one isn’t possible—say for a stage’s front-row audience—further risk reductions include:

3. Add background lighting to reduce light contrast to under 10%2

4. Avoid light-dark stripes1,2

5. If #4 isn’t possible, limit to five moving stripes or eight stationary stripes1

6. Avoid deep or saturated red1,2

7. Move light away from central vision to the periphery2

8. Stay under the brightness threshold of 20 nits1, or for further risk reduction, 1 nit2

I don’t like “The best way to win is not to play”-type guidance, because it implies that no one should ever try. However, putting the work into an intricate chase or gradient pattern can achieve a better effect than simple flashing, so if that’s achievable, seriously consider this mitigation:

9. Don’t flash lights

All the best to CD Projekt Red and their first week with Cyberpunk 2077’s release. As I was looking for articles and screenshots, I found that this goes far beyond them and this release.

Be good to your users,

— Shaun


1: Harding, G., Wilkins, A., Erba, G., Barkley, G.L., & Fisher, R. (2005). Photic- and Pattern-induced Seizures: Expert Consensus of the Epilepsy Foundation of America Working Group. Epilepsia, 46(9), 1423-25. doi: 10.1111/j.1528-1167.2005.31305.x.

2: IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers, IEEE Standard 1789, 2015


4: IGN preview: (Warning: Flashing light)