Do not use flashing or blinking text, objects, or other elements having a flash or blink frequency greater than 2 Hz and lower than 55 Hz.
Rationale
Text and objects that blink or flash can cause photosensitive epileptic seizures in susceptible individuals, particularly if the flash has a high intensity and is in the frequency range between 2 Hz and 55 Hz. This includes flashing text, turning graphics on and off or repeatedly changing between different images on the screen.
Development techniques
Use one or more of the following techniques to meet Checkpoint 5.2 from the IBM Software Accessibility Checklist:
- Use elements which do not blink or flicker.
- If the application must use blinking elements, use frequencies that are less than 2Hz or greater than 55Hz.
- Enable users to control the blinking rate through system settings. Windows allows users to customize the cursor blink rates through the Control Panel Accessibility Options. Developers can access these settings through the GetCaretBlinkTime function to emulate the system's cursor blink rate for custom cursors or for customized user interface elements. For more information on this technique, see the article "Flashing User Interface and the GetCaretBlinkTime Function" (link resides outside of ibm.com) from Microsoft.
The techniques above are required; the following techniques are recommended to enhance accessibility:
- Minimize the area of the screen which is flashing. Smaller areas are less likely to cause seizures.
- Avoid flashing that has a high level of contrast between the states. Some individuals are more susceptible to high intensity flashing.
Testing techniques
Test the software to ensure that it complies with accessibility requirements.
| Action | Result |
|---|---|
| 1. Manually verify that the software does not use blinking or flashing elements. |
Pass:
The software does not implement blinking text or objects. Fail: The software displays blinking text or objects. If the software has blinking elements, perform the next test to see if the blinking is between the range of 2Hz to 55 Hz. |
| 2. Display the blinking elements in the software. Run a program that displays the time interval between blinking text. |
Pass:
The time interval of the blinking text is less than 2 Hz or greater than 55 Hz. Fail: The time interval of the blinking text is between 2 Hz and 55 Hz. This interval can cause photosensitive epileptic seizures in susceptible individuals. |
©2001, 2008 IBM Corporation
Last updated January 24, 2008.