Thanks for your reply
Update: The input of the ballast is not for a variable resistor but for PWM 1-10v
can I use a simple circuit like this:
(found in this thread: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1288268120)
and will the 0-10v cause problems when the ballast expects 1-10v?
thank you
fubbi