Public bug reported:
WHAT YOU’RE TRYING TO ACHIEVE
I am trying to lock the screen and turn it off.
WHAT STEPS YOU TAKE
A) I press Super+L to lock the screen and make it go blank, i.e. turned
off.
B) Or I just wait 15 minutes for the screen to go locked and turned off,
as set in Settings > Power > Power Saving > Screen Blank ("Turn the
screen off...").
WHAT HAPPENS
The screen turns off for a few seconds, and then back on. Now the screen
is black, yes, but I can see that it's not really turned off, it's just
my LCD screen displaying a black image while the LED backlight is still
on.
WHAT YOU THINK SHOULD HAPPEN INSTEAD
I was expecting the screen to go into power saving mode, which means the
LED backlight and the LCD would be powered off. This way my LCD-LED
screen does not wear out over time, when locked.
ADDITIONAL TESTING
I did a logout/login into Ubuntu on Xorg (X11). From there, I tried
Super+L to lock the screen, again, and faced the same problem as on
Wayland.
I also tried "sleep 3; xset dpms force off" from the terminal. The
problem is more obvious this way: the screen comes back fully lit just a
few seconds later, with the desktop and everything clearly visible. (No,
I did not touch the mouse or the keyboard...)
I also restarted that same computer and screen combination under Windows
10. I found similar screen power saving as for Ubuntu, and it all works
as expected on Windows 10, regardless of my screen settings for input...
ADDITIONAL INFORMATION
I am on Ubuntu 24.04.1 LTS, on a regular Wayland session, with a
regular, new, mass-market IPS FHD LCD-LED screen: LG 24MR400-B.
Connected via HDMI cable. (DisplayPort on the computer side, with a DP-
to-HDMI adapter.)
This problem started to appear after I changed my screen for a new one.
I never had this problem before, on my old one. So, I tried changing a
few things on the screen itself, that LG 24MR400-B...
WORKAROUND
I found I just had to play with the "joystick" behind my screen:
Settings > Input > Auto Input Switch: Off (So there is no auto-switching
between HDMI and D-SUB.)
This way the screen behaves as expected and actually turns off the
LCD+LED, preventing it from wearing out too quickly.
WHY THIS BUG REPORT HERE ON LAUNCHPAD !?
It seems there are other people facing that same issue. On LG screens,
and Samsung, and Apple, and... etc. And they don't have this workaround.
I have read many similar stories on Google and Facebook... And that same
screen and computer combination works as expected on Windows 10.
I THINK IT'S A BUG...
INTUITIVELY, I would say that the HDMI cable is bidirectional, and that in some
cases, the monitor sends a signal, some information to the computer when the
screen goes into power saving mode. Ironically, this signal then causes the
graphics card to turn on again and this pulls off the monitor from power saving
mode. So, I think Ubuntu should ignore this signal coming from the monitor when
that monitor goes into power saving mode.
This is all just my personal opinion, of course...
** Affects: ubuntu
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2080585
Title:
Screen is blank and black, but still on after being locked
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