Thanks Daniel for your quick introduction to dimmers.
Now I see more the core of the problem.
For my use it will be probably best to buy a straight-out-of-the-box solution. I am thinking of buying a velleman K8064 dimmer kit that Massimo had suggested in another post. It's is a dc-controlled dimmer with an optical-isolated control-voltage input.
Another possible idea has come to mind:
What happens if I drive a classic light bulb with for instance 12V or 24V DC?
If this would work, I wouldn't have to worry about the zero-crossings from the AC and simplify and cheapen my design.
Marcus