Non-changing access path to "brightness" (LCD7 backlight)


I am running Linux 3.8.13-bone38 on a beaglebone black with

Some scripts I wrote access the brightness control of the
backlight of the LCD7 under /sys/...

Unfortunately the path to that control file seems not
to be constant from boot to boot.

At the moment it is:

But I see different numberings sometimes.

Is there any constant path to any control file, which enables the
scripts to control the brightness?
Or: Is there any constant path to a file, which content gives me
the correct path so I can stich togethter the resulting path
to the brightness control file?

Best regargs,