Reduce Flashing Lights - Get 'A' Certified

Flashing images and blinking lights can be very dangerous for some users, and uncomfortable for others. This post will help you follow accessibility guidelines to get your web app 'A' certified.

Who does this feature affect?

• People with photosensitivity (light - sensitivity) seizure disorders
• People with migraine headaches
• Everyone (Remember, accessibility features create a better experience for all)

How to implement:

1. Content on the page should not change or flash more than 3 times per second.
2. If it is necessary for the content to change more than 3 times per second:
   • Show the flashes on a small part of the screen (less than 21,824px square area)
   • The above square area is for the average screen, but if you know the size of the screen your content will be displayed on, there’s a formula you can use to calculate the safe square area: Calculation instructions
   • This should be the only flashing area on the page
3. Reduce the colour contrast for flashing content
4. Reduce the screen light contrast for flashing content
5. Don’t use fully-saturated red colour for flashing content
   
6. Use analysis tools to check if your webpage passes:
   • Photosensitive Epilepsy Analysis Tool
   • HardingFPA

How Not to implement:

• It’s not enough to have a button for the user to stop the flashing, because a seizure or migraine can be induced extremely fast. The user wouldn’t have enough time to press the button.
• Do not just put a seizure warning:
  • because people may miss them
  • children may not be able to read them
  

Examples of When an Application might use Flashing lights

• A slide in a presentation changing
• A video of explosions going off
• A video of a concert with strobe lights
• A video of lightning flashing

Interesting facts:

These guidelines were originally for TV programs, but now they’ve been adapted to computer screens taking into consideration:

• The shorter distance between the screen and the eyes
• That the computer screen takes up more of our field of vision when we’re looking at it
• An average of 1024 x 768 computer screen resolution

References:

Three Flashes or Below Threshold

Image References:

Lady with a migraine
Child on the computer
Fully saturated Red