I do want to point out that I am liking ubuntu mate so far, but it is annoying that ubuntu always resets my keyboard light to 50%. This is annoying since I am using a laptop, as it uselessly drains power.
The Ubuntu mate team should consider adding some options for the keyboard backlight.
You could have the system remember the last brightness for the keyboard, so people can still use the backlight if they want it.
I hope someone can fix this soon.
What brand / make is the keyboard? It would help as not every keyboard uses the same configs. It’ll be easier to attempt to debug the problem.
If it is a laptop keyboard, there should be a switch on the keyboard controlled by the “FN” key and whatever key controls the light!, F5/F6/F7 and so on, switch it off!. Look in your laptop/PC’s manual!. 
I have the same thing on a Dell latitude e5570 laptop.
Really irritating.
If you set it to of by the FN keys way it keeps getting turned back on after login or unlock.
Guys I know that, but I have to keep turning it down every time I do so. I am not saying it is permenent.
The ubuntu mate team needs to fix this.
EDIT:
By that I mean I do know how to turn the light down
Is there a setting in BIOS to turn it off completely?.
I have the same problem and it definitely happens when transitioning through the different stages of my booting process or unlocking process.
I can turn it off each stage and then the next stage it will come back on.
Example:
This looks to have been resolved in UPower (but I don’t think mate uses that) as the fix didn’t work for me.
https://bugs.launchpad.net/dell-sputnik/+bug/1510344
https://bugs.launchpad.net/dell-sputnik/+bug/1583861
It would be great if we can get someone to help us troubleshoot this type of problem.
The solution that would be highly recommended for me is the one that works in Mint which is that the ambient light sensor is used to tell the back-light what level to be at (known to work on Thinkpad and Dell). But I know that is wishful thinking on my part.
I have the same issue with the Dell XPS 13. I also have this problem when disconnecting my battery or reconnecting it along with waking from sleep. For some strange reason, even if I change it in the BIOS it still kicks on.
I have the same issue with Lenovo T440s, Ubuntu Ubuntu 16.04 LTS, Mate 1.12.1.
Has everyone done their updates?:
Yes I’v done them all
Ok, I figured out the fix, at least for me, hopefully other people will benefit. This is a bug with UPower. In order to fix it, you need to edit the file
/etc/dbus-1/system.d/org.freedesktop.UPower.conf.
You need to change:
send_interface="org.freedesktop.UPower.KbdBacklight"/>```
To
```<deny send_destination="org.freedesktop.UPower"
send_interface="org.freedesktop.UPower.KbdBacklight"/>```
Finally you should reboot. This should fix the problem. This was recently fixed in unity-settings daemon but needs to be fixed in the mate-settings daemon: https://bugs.launchpad.net/dell-sputnik/+bug/1510344@CrazyDesi I tried that and it made no difference for me. What laptop are you using?
I have a Dell XPS 13 9343. Make sure you are changing the correct option. There are two different things that say KbdBacklight. I had to scroll to see the second option. I accidentally changed the first option when I did it the first time.
Asus q400a same issue here
Hello,
This sounds somewhat familiar to a problem that I have faced earlier this year when I purchased a Cooler Master keyboard + mouse Devastator combo.
The gimmic was that both the mouse and the keyboard had flashing lights dimming from/to all colors in the rainbow.
So I plugged the mouse in and it worked fine. But the keyboard had 0 light poping up on it yet it worked fine. After some mixed interactions with (I even claimed a RMA thinking it was defective), my girlfriend simply plugged it into a windoze 10 machine and THE LIGHTS WENT ON! Plugging it back however into a Linux host brought the same initial result: keyboard worked but not the lights.
At ths point I simply lost all hope of getting it working and reverted back to a “regular” keyboard.
This is probably not the answer you were looking for but, hey, true story nonetheless.
Cheers,
DLS
Let’s bring this VERY USEFUL Thread alive. 
I havent any Dell. Mine’s Asus Zenbook UX32VD.
That being said, the fix you proposed works for me, independently from what line I change from “allow” to “deny”. (Works with first as well as second line)
Problem: The Zenbook has no ON and OFF backlight switch. You can turn it off and on using Fn + LIght up or light down, until it is completely off, or completely on (Has 4 level OFF > LOW ON > MIDDLE ON > HIGH ON)
As i said, it works, but completely disable the possibility to turn the keyboard light on when it’s needed.
In the Zenbook, even when the screen dim down to save power, and then you dim up again moving the mouse, the keyboard light turn on again, even from OFF state.
Using Ubuntu Mate 16.04 with Mate 1.16.1 here.
Works fine on Lenovo ThinkPad X230, can turn on keyboard light any time I wish. Thanks!!!
fANTASTIC! This fix works beautifully for me.
My config:
Thinkpad X230 running ubuntu mate 16.04.2.
The keyboard backlight used to randomly keep turning itself on, changing the conf file as per your comment totally fixed this. Thanks @CrazyDesi
Loving ubuntu mate so far.
This approach fix this problem in my Lenovo Thinkpad T450