Description of problem:
Use of xrandr command to lower brightness infrequently not work.

Bug details:
My video port is eDP1. So, to lower brightness I use:
xrandr --output eDP1 --brightness 0.3
It was O.K till about 10 days ago when I started to experience failure of this command ! I entered it correctly & receive no any error message in terminal but brightness not changed ! I have to close terminal & reopen it & re-entering this command again !
This bug occur infrequently but it is new phenomenon. 

Version-Release number of selected component (if applicable):
xrandr program version 1.5.0
Server reports RandR version 1.5

How reproducible:
xrandr --output ePD1 --brightness 0.x

Steps to Reproduce:
1.
2.
3.

Actual results:
Brightness level not lowered

Expected results:
Lowering brightness level

Additional info:
Lenovo ThinkPad e550