Take a good look at https://wiki.archlinux.org/index.php/Backlight, it provided the workaround used below.
Don't forget to restart JWM after saving the edits.
Copy below into /etc/xdg/templates/_root_.jwmrc and /root/.jwmrc , add it before the first <RootMenu> entries
Code: Select all
<RootMenu label="" labeled="false" height="24" onroot="6">
<Program label="1" icon=""> echo 1 > /sys/class/backlight/acpi_video0/brightness</Program>
<Program label="2" icon=""> echo 2 > /sys/class/backlight/acpi_video0/brightness</Program>
<Program label="3" icon=""> echo 3 > /sys/class/backlight/acpi_video0/brightness</Program>
<Program label="4" icon=""> echo 4 > /sys/class/backlight/acpi_video0/brightness</Program>
<Program label="5" icon=""> echo 5 > /sys/class/backlight/acpi_video0/brightness</Program>
<Program label="6" icon=""> echo 6 > /sys/class/backlight/acpi_video0/brightness</Program>
<Program label="7" icon=""> echo 7 > /sys/class/backlight/acpi_video0/brightness</Program>
</RootMenu>
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<TrayButton label="" icon="/usr/local/lib/X11/mini-icons/idea16.xpm">root:6</TrayButton>