> However, unless I am mistaken the characteristic which will determine
> whether a computer screen will be likely to trigger a fit is the screen
> refresh rate. This is I believe lower on portables than on desktop
> monitors so a portable might actually increase the likelyhood of a fit. On
> the other hand it may also be that there is a greater "persistence" in the
> laptop's screen which will reduce the effect of the lower refresh rate.
> When I was researching this for an article on epilepsy I did not find
> anyone able to give categorical answers. The best advice came from the
> scottish epilepsy association.
LCD screens don't refresh in the same sense as a CRT in a standard
monitor. Each pixel in your 640x480 VGA or 800x600 SVGA screen is
related to a 'cell' on the LCD screen. Matrix addressing allows the
contents of the cell to be changed. In the case of a TFT LCD screen
the switching characteristic of the LCD is assisted by a transparent
transistor (Thin Film Transistor) associated with each cell.
A CRT (Cathode Ray Tube) works by moving an electron beam from top
to bottom of the screen in horizontal lines. The refresh rate
determines the number of times it does this per second. Generally,
the faster the better.
The advice we have received suggests that if a CRT is to be used it
should be as small as possible (9 inch?) and colours should be
selected for minimum light output, so that flickering is minimised.
So change the standard Windows black on white text to something that
is comfortable on black.
Regards
Paul Dilley, Technical Manager & dis-forum co-owner
Computer Centre for People with Disabilities, University of Westminster
** The Central London Access Centre ** NFAC **
Tel: +44 171 911 5000 Fax: +44 171 911 5162 http://www.wmin.ac.uk/ccpd/
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