PWM makes LCD backlight strobe

I'm running an LCD (model GDM1602K) using LiquidCrtystal plus I am controlling backlight and contrast using PWM outputs. The backlight uses a transistor to amplify current required to drive into the LCD.

My problem is the obvious strobing of the LCD pattern, due waveform of the PWM control signals I suspect.

Whats a good way to control backlight from arduino? I tried to smooth the PWM using simple RC but no go. :-?
Any suggestion welcomed !

My problem is the obvious strobing of the LCD pattern, due waveform of the PWM control signals I suspect

The minimum PWM frequency is normally just under 500Hz, well above what can be perceived by the eye - have you changed any of the PWM timer settings, or measured the frequency

I haven't played with PWM freq's, all normal.

It looks a bit like an old TV would sometimes in poor reception, slow lines rolling up the screen. I understand what you're saying about 500Hz, but I reckon I'm seeing a "beating" pattern .... like you get when two close frequencies produce a difference... and in this case the diff is slow enough to see.