Comment 5 for bug 1639517

Christopher M. Penalver, re backlight cycle.

Booting, grub config: no workaround, "quiet splash", reboot - I note following cycle:

Grub menu - gray backlight (brightness same as grub menu background) - then a flash (white), not covering the whole screen - black( 0% brigthness, lasting 6 sec) - gray like before.

cold start:

grub-menu - gray - flash (white), not covering the whole screen -a cycle of 16 times: black and gray - the last gray

note:
runnig Ubuntu, brightness cannot be changed
running Windows10, no brightness problem.