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SC 2.2.2 (Blinking) and contrast ratio

From: Christophe Strobbe <christophe.strobbe@esat.kuleuven.be>
Date: Wed, 12 Sep 2007 11:57:11 +0200
Message-Id: <>
To: wcag <w3c-wai-gl@w3.org>


The following question came out of some work on the Unified Web 
Evaluation Methodology (UWEM) [1].
The May 2007 draft of WCAG 2.0 defines blink as "turn on and off 
between 0.5 and 3 times per second", with a note saying: "The slower 
blink is in contrast with flashing, which refers to rapid changes in 
brightness which can cause seizures. See general flash and red flash 

However, the definition of blink does not specify a contrast ratio 
between the on and of states, so any blinking fails the success 
criterion, even if the contrast between the two states is very low. 
Of course, low contrast would fail SC 1.4.3 (Contrast (Minimum)), but 
evaluators, especially automated tools, would want to establish 
whether blinking content fails SC 2.2.2 by itself, regardless whether 
it passes or fails SC 1.4.3.
So, my question is: does *all* blinking content fail SC 2.2.2? (I 
assume it currently does.) Should we add a note about this to the 
definition of blink?

Best regards,


[1] <http://www.wabcluster.org/uwem1_1/> UWEM is based on WCAG 1.0; 
checkpoint 7.2 covers blinking content.

Christophe Strobbe
K.U.Leuven - Dept. of Electrical Engineering - SCD
Research Group on Document Architectures
Kasteelpark Arenberg 10 bus 2442
B-3001 Leuven-Heverlee
tel: +32 16 32 85 51

Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
Received on Wednesday, 12 September 2007 09:57:22 UTC

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