Fn key to adjust brightness no long working in my Lubuntu

[Marlon Ng]

My laptop is running Lubuntu.  It used to have this file:

/sys/class/backlight/acpi_video0/brightness

but it's now replaced with this:

/sys/class/backlight/samsung/brightness

(in other words, the acpi_video folder is replaced with samsung folder)

Now I can't used the Fn key + up or down arrow to adjust brightness.

1.  Is this due to recent updates?

2.  I recently installed another desktop environment in my Lubuntu, which
proved to be buggy, so I uninstalled it.  I wonder if it has anything to do
with Fn key not working?

3.  The Fn key + right or left arrow button to adjust sound works fine;
only problem is the brightness adjustment (Fn + up or down arrow)

Any ideas?
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