A somewhat overly technical answer, but you did ask "is it possible..."
Open Terminal and go to
/sys/class/backlight, then into the backlight control's directory (the name varies,
acpi_video0 in my laptop), then read the files
actual_brightness. GNOME limits itself to 5 levels between zero and max, but the actual hardware usually has at least 10 levels. If the
max_brightness file says "10" or more, a finer adjustment will be possible.
$ cd /sys/class/backlight
$ cd acpi_video0
actual_brightness device@ subsystem@
bl_power max_brightness type
brightness power/ uevent
$ cat max_brightness
You can write the desired level to a file named
brightness in that directory, but in this example GNOME's own tool is used, which does not require root access.
$ pkexec /usr/sbin/gnome-power-backlight-helper --set-brightness 7
or in more recent versions of GNOME the path changed to:
$ pkexec /usr/lib/gnome-settings-daemon/gsd-backlight-helper --set-brightness 7
As Linker3000 said, there might be a GNOME Panel applet for controlling the brightness. Right-click the top panel and choose "Add".