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Why This is Important
Flashing lights can induce seizures for people with epilepsy. Avoiding them reduces the chance of a medical emergency.
Blind and visually impaired people use screen readers to interact with websites and apps. A screen reader is a type of assistive tech that converts things on screen to audio and/or braille. It's important that things are understandable and interactive to screen readers.
Keyboard accessibility is essential for people who do not use a computer mouse (which might be because they have unpredictable or very specific movement due to a motor disability). Many Blind and visually impaired people also use keyboard interactions in order to use their screen reader.
Error support is accessible to people with a diversity of disabilities. A cognitive disability might affect how a person perceives and understands things. A physical disability might lead to unpredictable movement. Other factors such as environment, stress, and multi-tasking may also lead to errors.
In order to be accessible, gestures and interactions must account for people with physical and motor disabilities, who might have unpredictable or very specific movement.
Flashing lights can also cause pain or discomfort for people who are sensitive to light or be distracting to people with ADHD, Autism, or other cognitive disorders. This includes sirens, strobe lights, and other visual flashing effects.
This references WCAG criteria 2.3.1 Three Flashes or Below Threshold (Level A) and 2.3.2 Three Flashes (Level AAA).
Level AAA compliance is considered more difficult to meet because it requires more resources to fulfill. It also might encompass conflicting access needs (meaning what is accessible to some might be inaccessible to others). Use your best judgment of your target audience and your team's capabilities to determine if this is a pragmatic goal to reach.
How to Implement This
Do not use flashing lights
According to WCAG, this refers to any lights that flash more than 3 times per second. Red lights are particularly triggering and should be avoided.
Learn more from the Epilepsy Society.
Provide a content warning
If displaying flashing lights is unavoidable, e.g. if it's video recording of an art installation or a concert performance, provide a content warning that is highly noticeable and allows for the user to exit or close the potentially triggering content.
Most social media platforms automatically play videos and do not include a way to add warning on the platform. If the video includes flashing lights, I recommend adding a 5-second title slide to the beginning of the video as well as a warning in the caption.
Interesting further reading
How to Test This
- Make sure that flashing lights would not pose harm to the tester
- Manually navigate the website/app and check for any triggering flashing lights
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