There is an easy workaround for this. we can use a command line utility named xbacklight and using it fix the brightness to a specific value at every system startup so that you don't have to adjust it every time.
follow these 3 Simple Steps:
1. Install xbacklight
sudo apt-get install xbacklight
2. Search and open Startup Applications from the dash
3. Now, click the add button and name it 'xbacklight' or anything and set the command to any desired value like shown in the image below (I prefer it set to 20%). Save it.
Done! Restart your laptop to see effect.