On Fri, 22 Apr 2005, Robert Rolf wrote:

> I have 'normal' persistence so low refresh rates don't bother me.
> But I can also spot LED lights or other strobed lighting (LED sign
> boards) because they make distinct spots of light as I pan my
> viewpoint across them.

Try watching the computer screen while munching a sandwich (or something 
crunchy).

> Some people do appear to have much shorter persistence than normal.
> One friend of mine, who was a military pilot, can't stand to look
> at my CRTs because they flicker too much for him. Having shorter
> persistence, and so lower blur when flying near ground,
> is probably an advantage to a pilot. I wonder what the chemistry
> difference is.

It's very likely not chemistry but nervous system responsivity.

> E... has no problem looking at laptops since their LCDs are very
> slow to respond (80msec IMS), so I rather doubt that laptops can be
> causing headaches from the REFRESH. They may be causing headaches
> because of seating posture or other mechanical issues (close focus etc.).

Laptops with faulty (or dimmed) bakcklights are known to have all sorts 
of annoying flicker. It could be that. The discharge path in a 
undervolted tube takes the shape of a moving or meandering spiral. The 
frequency of the spin depends on a number of factors but it can be in 
flicker range.

I have read somewhere that LED and VFD displays must be muxed at 70+Hz 
frame rate to avoid flicker (probably more for cockpit applications). 
You can often see the flicker with the corner of your eye. It 'helps' if 
the display is quite dark and *not* red. Apprently the rods have higher 
speed response than the cones but the cones can be really resistive to 
flicker in certain ranges.

Peter
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