Net Neutrality...

William Herrin bill at herrin.us
Fri Jul 18 23:22:04 UTC 2014


On Fri, Jul 18, 2014 at 6:48 PM, Owen DeLong <owen at delong.com> wrote:
> On Jul 18, 2014, at 11:35 , William Herrin <bill at herrin.us> wrote:
>> An LED screen doesn't refresh the way a CRT does, right? The light
>> doesn't flash and fade, it stays constant until the next change. So
>> why would a 30 hz refresh rate make any difference at all for tasks
>> which update the screen less often than 30 times a second? Mike did
>> say he used it for doing software development.
>
>However, the brightness of any particular color of any particular
>pixel in any LED screen is usually controlled by a process known
>as Pulse Width Modulation (PWM) where the LED actually turns
> on and off several thousand times per second and modifications
> of the ratio between the on-time and off-time in those cycles are
>used to control the apparent brightness.
>
> However, most "LED Screens" aren't actually LED screens, most of them are
> LED backlit CRT Screens. (I didn't look at the specs on this one in detail, so
> I don't actually know which type it is).

Hi Owen,

You probably meant LED backlit LCD (liquid crystal display) screens,
yes? As opposed to an LCD panel backlit with fluorescent tubes? LCDs
don't have a flicker rate either, unless they're particularly badly
implemented.

http://en.wikipedia.org/wiki/LED-backlit_LCD_display

Interesting point about PWM controlling the LED brightness, although
that won't be tied to screen's overall refresh rate either. The pulse
timing will be the same whether your overall refresh rate is 30 fps or
300.

(And for those of you who don't bother turning off your flat panel
monitors at night because what the heck, they won't burn in right?...
That's a mistake. You won't hurt the LCD but the cold cathode
fluorescent tube backlights are wearing out.)

Regards,
Bill Herrin


-- 
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>
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