"Fn" + "Left/RightArrow" buttons change brightness for 3 levels; not 1 level

[Qua Purna]

Halo, Forum Members.

Lubuntu 13.10 , 32bit.

On my netbook, to set the screen brightness is by using the "Fn" +
"Left or Right Arrow".

If I push the button-combination once, the brightness changes for 3
levels, instead of 1 level.
e.g. from level zero of brightness, I push Fn+RightArrow once, then
the brightness is up for 3 levels.

Can I fix this so that the level of brightness will be up or down for 1 level  ?


Thanks.