Interference from other devices also causes flickering. For example, laptop power supply's on the same circuit, which our technician discovered. Move the power supply to another circuit and hey presto, no flicker.
Tim
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-----Original Message-----
From: Discussion list for disabled students and their support staff. [mailto:[log in to unmask]] On Behalf Of Simon Iremonger (dis-forum list)
Sent: 17 September 2014 00:10
To: [log in to unmask]
Subject: Re: Refresh/Flicker rate PCs vs Macs
On 2014-09-12 08:58, Ian Webb wrote:
> There is no flicker or refresh rate for flat screens.
> Ian Webb Centre Manager ATOP Ltd
> I am wondering if there is any empirical/medical evidence that the
> refresh/flicker rate from a PC screen can detrimentally affect someone
> with epilepsy; i.e. induce [...] a seizure?
> John Hodgson Study Needs Assessor
Well, Actually, I would like to dis-agree!
"refresh rate" is the rate the display content is updated.
The "flicker rate" on an LCD screen basically comes from the backlight driving circuitry, I have seen a lot of backlights which (depending on your definition) you might consider to have flicker.
On CRT screens both Refresh and Flicker rate were the same thing, but that is no longer the case with LCD screens.
This backlight flicker is often in the ~200hz range and typically depends upon brightness setting (full brightness sometimes eliminates the modulation of PWM dimming).
I suspect this is too fast to affect epileptics but especially at lower frequencies it can definitely cause headaches in some people.
We were actually lent a BenQ "eye-care" monitor which explicitly gets rid of the flickering backlight, see my report/notes:-
http://www.iremonger.me.uk/noidx/BenQ-BL2710.pdf
Although, as I say, its' perfectly possible to find 'other' flicker-free monitors, but the trouble is knowing what-is-what... Is good to see at least one manufacturer making the issue explicit and selling a range that definitely don't have that problem.
Hope thats' helpful,
--Simon
p.s. Is possible to make a very lo-tech simple gadget with headphones, battery, switch, resistor, and a LDR (Light dependent resistor) so as to allow you to 'hear'
the flicker from various sources...
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