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On my Dell Latitude E6400, the minimum brightness level seems to be set to an incorrect and way too low level; the lowest brightness setting (both via the Fn+Up/Down keys and the control panel/mobility center) totally turns off the backlight, where I would expect it to still have a slight backlight.

The problem is that this messes up the adaptive brightness service; when the light sensor doesn't detect any light it sets the backlight to the lowest level, except the lowest level is a total absence of backlight and that makes the adaptive brightness totally unusable.

Edit: the adaptive brightness problem is (hopefully) solved with this ALR curve, but the question still stands - it shouldn't be possible (nor useful) to lock yourself out of the machine by not being able to read anything on the screen (the Fn keys aren't reliable enough and sometimes don't work after standby, thus you need to blindly open up the mobility center and set the brightness back up a bit).

I have the latest BIOS (version A34 if I remember correctly), and I installed the latest Intel display drivers, nothing changed. I'm looking for a registry hack or something that can change the lowest brightness level to something higher, where the backlight will still be active.

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  • The default expectation for keyboard backlight brightness is for the lowest setting to turn off the keyboard backlight. That's true in a majority of systems. It differs from screen brightness, in this way, because screen brightness often will not shut off the display at the lowest setting. Is there an option in the adaptive brightness service to raise the minimum level?
    – James Brewer
    Sep 15, 2014 at 20:26
  • @JamesBrewer thanks to Microsoft it's hardcoded in the default Adaptive Brightness service. I am able to change the ALR curve (the function that maps sensor brightness to screen brightness) but 0 sensor brightness is always 0 screen brightness no matter what.
    – user256743
    Sep 15, 2014 at 20:28
  • The ALR table should allow you to set a minimum offset percentage based on illuminance level (measured in lux). Because it's a percentage, as long as you don't set it to 0%, it should still light up (ex: 0 lux, 1% offset vs 3000 lux, 200% offset). Bear in mind that the offset must increase as illuminance increases (curve must be a positive, upward trend)
    – James Brewer
    Sep 15, 2014 at 20:56
  • @JamesBrewer I've tried it as described in this answer of mine, however I still couldn't get it working right and finally gave up on it. Do you have a working ALR curve with such offset by any chance ? (or a verified working example, because my attempts didn't work quite well and I always ended up with a black screen)
    – user256743
    Sep 15, 2014 at 21:00
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    @JamesBrewer thanks for trying to help, here's the slightly modified ALR curve that currently works, let's hope it stays that way. This question still stands since it's pretty annoying to be able to turn the brightness too low and lock yourself out of the machine (the Fn keys sometimes stop working after standby/sleep).
    – user256743
    Sep 15, 2014 at 22:24

1 Answer 1

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In case there's someone still interested in this, there is a solution. This solution might be shooting a bird with a cannon, but it should work.

First off, with NirCmd, create a batch file that increases the brightness by a certain amount. Then, go into the event viewer, and under Applications and Services>Microsoft>Windows>Diagnostics-Performance click on the "operational" log. In there you should find an event where it says "Windows has resumed from standby" (on Windows 7 the event code is 300, and my guess is that it would be the same on newer versions of Windows). Attach a task to one of those events, and then set that task to be the batch file you created earlier. Then, whenever you resume your system, the brightness will be increased by the amount specified so that you don't have to hunt around in the dark.

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