Mobile Accessibility Guidelines - Design

Flicker must not

Content must not visibly or intentionally flicker or flash more than three times in any one-second period.

Visual flicker, flashing and strobe lighting can affect anyone, but some users will be more susceptible than others. Symptoms may include eyestrain, dizziness, fatigue, headaches, migraine, and nausea. Users with medical conditions such as Ménière’s or photosensitive epilepsy can be severely affected, experiencing vertigo, hearing loss and seizures.

A well-documented example of the effects of flicker is Pokémon Shock.

Lots of motion on screen can also cause discomfort and nausea for some people, particularly users with balance and eye movement disorders.

Avoid motion that the user has not chosen to opt-in to, unless it is very brief and small.

If flicker is integral to the content, warn the user before they reach the content and allow them to choose not to opt-in to viewing it.

Where editorially appropriate, provide an alternative version of content that does not flicker but is as close to the original as possible.

For further information on flashing images and movement see the GEL Guideline How to make accessible animation, WCAG 2.1 “general flash and red flash thresholds” and BBC Editorial Policy (BBC access only).

iOS

Not Applicable

Android

Not Applicable

HTML

Not Applicable

Testing

Procedures

  1. Verify where in the page/screen content flickers.

  2. Using the Flicker Tester hold the camera close to a light source.

  3. Save the flicker curves index, frequency and flicker percentage.

  4. Verify this meets the flicker requirements or a warning and on/off button are provided.

    Flicker Tester, Note: the BBC also has a Screen Flicker Tool for staff on the internal network.

Outcome

One or more of the following is true:

  • A warning and an off button is provided.
  • Content passes the flicker test requirement.