Finally I counted a few light pulses with the one-wire counter. No big circuit with the Velleman MK120R kit but just a photodiode and a resistor hooked up to the counter module. I got the idea from looking at the schematics for the Hobby Boards 1-Wire Lightning Detector. The counting circuit is a phototransistor (in an optocoupler) and a resistor. With a bit of tweaking on the resistor I eventually got the counting circuit to count 2 light flashes from a flashlight. With some more tweaking of the resistor value I think I could count red flashes from the electricity meter.
I also installed the lightning detector under the roof. But it is too close to the wiring of the house I think: sofar all counts are related to me being in the attic and turning on the light. In a 'real' setup I think it needs to be away from the house. Something to keep in mind for the project sundial weather station.