| |||||||||||||
|
| |||||||||||||
Observations on power managementObservations on power managementPosted Nov 24, 2008 18:47 UTC (Mon) by jwb (guest, #15467)Parent article: Observations on power management
"A black screen takes up as much power on a TFT as a white one."
Almost true. A black image actually takes measurably more power than a white one on an LCD display. Black is the worst power state for a flat panel display. It would be better to simply turn off the backlight.
(Log in to post comments)
Observations on power management Posted Nov 24, 2008 20:17 UTC (Mon) by MattPerry (guest, #46341) [Link]
Can you provide a source to support that statement?
Observations on power management Posted Nov 24, 2008 20:27 UTC (Mon) by jwb (guest, #15467) [Link]
Here, let me google that for you:
http://techlogg.com/content/view/317/
And I've measured my own monitor as well. If you think about how an LCD works, it's logical that 100% black requires the highest current consumption in the panel.
Observations on power management Posted Nov 25, 2008 1:21 UTC (Tue) by sbergman27 (subscriber, #10767) [Link]
Yep. My 22" measures 26 watts while white and 27 watts while black. (My kill-a-watt only displays in increments of 1 watt.) I had always thought it would be the other way around. But now that I think about it, when a watch battery dies, the display turns all silver and not all black. It takes power to make black.
Backlights Posted Nov 25, 2008 15:30 UTC (Tue) by sladen (subscriber, #27402) [Link] The digital watch you're describing is using a simple LCD display (not a VFD/TFT/LED). If you were to flip the polarising glass over on the watch (more easily done on a household/school calculator) then you will have a display that default to black, with clear (reflected) writing. In a self-illuminated colour TFT display, the bright white backlight is used as a starting point, and selectively blocked out (meaning "black" never looks quite black). Transreflective screens complement the blacklight with reflected incoming light (as with the digital watch/calculator's primary source).
Finally, high-end recent flat-screen displays are now are able to selectively shut-off/tone down the output of the backlight in areas where the image is dark or black; by avoiding producing extra light in the first place, less of that light needs blocking to produce a satisfying black.
OLED? Posted Nov 26, 2008 15:39 UTC (Wed) by dmarti (subscriber, #11625) [Link] I'm saving up for an OLED monitor when those come out (the TV at the Sony store is beautiful). OLED doesn't have a backlight and AFAIK black is off.
Observations on power management Posted Nov 24, 2008 20:31 UTC (Mon) by pebolle (guest, #35204) [Link]
"It would be better to simply turn off the backlight."
Isn't that just what the author suggests: "Summary: If the user has not requested an animated screensaver, turn the screen off immediately rather than drawing a black screen."?
Observations on power management Posted Nov 24, 2008 20:33 UTC (Mon) by jwb (guest, #15467) [Link]
Yes, absolutely I agree. I was just trying to underscore the stupidity of the current batch of black screen "savers". For instance, Ubuntu by default still blacks out the screen for several minutes before disabling the backlight, as if this made any type of sense for today's computers.
Observations on power management Posted Nov 25, 2008 4:28 UTC (Tue) by Richard_J_Neill (subscriber, #23093) [Link]
> For instance, Ubuntu by default still blacks out the screen for several
> minutes before disabling the backlight, as if this made any type of sense > for today's computers.
Actually, this isn't as daft as it sounds. Apart from the disk, the LCD is the most likely thing to fail in a laptop - whether the backlight dies totally, or just dims or "yellows" over time. CCFL backlight life is hurt by both runtime and number of start-cycles. So, unless battery life is really really at a premium, you want to avoid turning off the backlight when the user is still actually using the machine.
Observations on power management Posted Nov 25, 2008 13:14 UTC (Tue) by renox (guest, #23785) [Link]
I disagree with you here: this doesn't make sense for the computer, but it make sense for the user.
If the user stays too long with doing anything the screen will idle to black and then the backlight will be disabled: it make sense to have an idle screen as quite often the user will move the mouse to re-activate it.
Should the idle screen be white or black?
Observations on power management Posted Dec 1, 2008 8:26 UTC (Mon) by MKallas (guest, #38539) [Link]
As soon as I lock the screen, the background light should turn dark.
Besides, my netbook uses a LED backlight so I don't have to care about dying cathodes. :-)
Observations on power management Posted Nov 24, 2008 21:07 UTC (Mon) by nix (subscriber, #2304) [Link]
Of course this only applies if you're displaying a screensaver image. If,
say, you're display an xterm (almost totally black, a bit of white text), turning off the backlight is a rather bad idea, and you just have to eat that tiny extra bit of power.
Observations on power management Posted Nov 25, 2008 3:17 UTC (Tue) by ncm (subscriber, #165) [Link]
Yet another argument for defaulting to black text on a white background: it doesn't just save your eyes, it saves power.
Observations on power management Posted Nov 25, 2008 13:48 UTC (Tue) by nix (subscriber, #2304) [Link]
Black text on a white background hurts my eyes (not surprising given that that means I'm basically staring into a light bulb).
Observations on power management Posted Nov 25, 2008 21:50 UTC (Tue) by ncm (subscriber, #165) [Link]
Turning down the brightness of the white background saves your eyes and saves power, too.
Observations on power management Posted Nov 27, 2008 12:30 UTC (Thu) by lysse (guest, #3190) [Link]
Contrast is a friend for those of us with dodgy eyesight.
I miss monochrome monitors; I don't suppose they're made any more, are they? A shame; I'd love to have a 600dpi monochrome A3-sized TFT on my desk - and given that 225dpi colour displays can be made, I think it's possible...
|
|
||||||||||||