When I lock my screen using Ctrl+Alt+L, my screen goes blank. I am happy with this.

However, the back-light seems to turn off and on every around 5 seconds, even though the screen stays black. It's possible to see that the back-light turns off and on since the screen "blackness" changes.

I assume this behavior eats a lot of my battery when it shouldn't. How can I debug/fix it?


The laptop is a HP stream 14. Kernel version 4.15.0-58-generic, but I'm not using HWE. I didn't know about HWE, but as the model is now some years old I'm not sure it'd make a difference?

Output of sudo lshw -C video:

   description: VGA compatible controller
   product: Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Integrated Graphics Controller
   vendor: Intel Corporation
   physical id: 2
   bus info: pci@0000:00:02.0
   version: 35
   width: 64 bits
   clock: 33MHz
   capabilities: pm msi vga_controller bus_master cap_list rom
   configuration: driver=i915 latency=0
   resources: irq:121 memory:90000000-90ffffff memory:80000000-8fffffff ioport:1000(size=64) memory:c0000-dffff
  • Which kernel are you using? (ie. do you have HWE enabled on the your 18.04 system). The easiest thing to try would be using HWE kernel (if you're not using it, maybe even non-HWE if using HWE currently) assuming there aren't any specific reasons on why you have HWE disabled/enabled. (wiki.ubuntu.com/Kernel/LTSEnablementStack) Details on your graphics hardware may also provide more clues (ie. sudo lshw -C video) – guiverc Jan 17 at 5:26
  • Why are you using that kernel? Your system is months behind what you should be running (ie. you're running a kernel from Aug-2019 so possibly haven't had upgrades since then..). I would suggest sudo apt update; sudo apt full-upgrade to ensure you install all upgrades available, reboot for security reasons alone, then re-assess if the issue has been fixed in the updates since August. The main benefit of HWE is you'll get to use later software stacks & thus upgraded kernel modules (drivers) as only security fixes themselves are back-ported; not newer features... – guiverc Jan 17 at 11:24

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