Some people with photosensitive epilepsy can have a seizure triggered by displays that flicker, flash, or blink. This is particularly the case if the flash has a high intensity and is within certain frequency ranges.
There are a number of guidelines and laws that online content producers may want to consider.
World Wide Web Consortium (W3C) guidelines on flashing on websites
The W3C was created in October 1994 to develop protocols and guidelines that ensure long-term growth for the Web. The Web Content Accessibility Guidelines 2.0 were published in 2008 in an effort to improve the accessibility of the web for disabled people.
In connection with photosensitive epilepsy, as part of good practice, it recommends that web pages do not:
- Contain anything that flashes more than three times in any one second period or
- Flash below the general flash and red flash thresholds
In addition, they suggest:
- Reducing contrast for any flashing content
- Avoiding fully saturated reds for any flashing content
- Reducing the number of flashes even if they do not violate thresholds
- Providing a mechanism to suppress any flashing content before it begins
- Slowing down live material to avoid rapid flashes (as in flashbulbs)
- Freezing the image momentarily if three flashes within one second are detected
- Dropping the contrast ratio if three flashes within one second are detected
- Allowing users to set a custom flash rate limit
If the user is unable to control the flickering, blinking and moving (this includes stopping these effects from starting), then these effects should not be used.
Disability discrimination legislation
In some countries, such as the UK, it is illegal to discriminate against people with long-term health conditions.
If your website, video or other piece of online content breaks the W3C good practice guide (above), then you should consider if there is a valid reason for it to do so. If there isn’t then you may wish to edit your content to make sure it meets the W3C guidelines.
If you feel that there is a valid reason why your content should break the W3C guidelines, then we strongly urge giving a warning before the flashing starts (for a video, then before the user starts to play the video).
If you don’t alert people with photosensitive epilepsy to flashing and someone has a seizure as a result of your website or video, you may be breaking the disability discrimination laws.
Use of TV broadcasters’ guidance
The UK’s disability discrimination legislation led to the British TV regulators producing a ‘Guidance Note for Licensees on Flashing Images and Regular Patterns in Television’. This gives television broadcasters guidance on the use of flashing images in their programmes. Some online producers use their guidelines to check their content.