I don't know how they get this voltage, but in my technical specification it is mentionned that I should use 135 VAC maximum voltage in mode Bright.

I've come up with an arrangement which uses two different string lengths and a transistor cut-off to limit current without spending too much time in the linear region.

In the lower voltage range, only the shorter string is active, because the combined Vfs of the longer string aren't overcome.

In the higher voltage range, the longer string starts conducting, and current through it activates a pair of NPNs which cut off current through the shorter string, preventing it from being overloaded by the higher voltages. It's not elegant or pretty, but it just might work. It would take some tweaking to get the exact brightness levels you want, but I think the basic concept is feasible:

 

So now we will wait to see what the TS thinks about it.

 

The statement in post #1 "I should use passive components" make me think this is some kind of school project with such a restriction.

Les.

 

The statement in post #1 "I should use passive components" make me think this is some kind of school project with such a restriction.

Les.

This seems like a retrofit project, replacing florescent tubes with an undefined LED arrangement. The very big challenge is the totally different power requirements of LED devices.