Whenever this question is asked, the answer is always "Please, do not do it"
Here is part of a reply from J.E McGimpsey some time ago:
US Government sites are prohibited by law from displaying flashing text
(between 2 and 55 Hz) due to triggering seizures in those with
photosensitive epilepsy.
http://www.section508.gov/IRSCourse/mod02/021401--.html
Many other organizations try to conform to section 508.
best wishes
--
Bernard V Liengme
Microsoft Excel MVP
http://people.stfx.ca/bliengme
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