How to increase brightness in smaller steps?

Install xbacklight by opening a terminal with Ctrl+Alt+T shortcut and type this:

sudo apt-get install xbacklight

then after installation, type these commands in terminal:

xbacklight = 10
xbacklight = 20
xbacklight = 5

this may help.

There is a file in Ubuntu which stores numerical integer value of brightness. you will find 3 files in the directory /sys/class/backlight/<VGA>directory replace directory with intel_backlight for intel cards.

You will find the max brightness value in max_brightness file and according to that value set the brightness in brightness file.

For Xubuntu LTS

Firstly, install xbacklight

$ sudo apt install xbacklight

Secondly, check whether you have control over the backlight.

$ xbacklight -1
$ xbacklight +5

Should these commands result in a No outputs have backlight property error, then follow these remediating steps before proceeding.

Once xbacklight -1 and xbacklight +1 work from the command line, proceed with assigning these commands to respectively the XF86MonBrightnessDown and XF86MonBrightnessUp keys. This is done by hitting those keys when asked by the Settings → Keyboard → Application Shortcuts application.

Finally, reboot for these changes to take effect.