That's about as unenforceable of a law as I've ever heard about. A 1 Watt source can emitt different lumens as just mentioned. A 1 Watt laser will burn holes in wood and set many things on fire. I'm pretty sure you can buy a 0.5 Watt laser that's handheld with a battery in the case like a flashlight. A 1 Watt incandescent source is not even a good nightlight.
Also depends on the optics in front of the light. A 1 Watt LED source without optics emitts in essentially a half dome. Very dim. Put a lens or reflector in front of it and you have a useable beam. Focus it too much and only a tiny spot on the road will be illuminated, and there will be no light emitted off to the sides at all for visibility to drivers.
The OP should work to elect smarter representatives in his locale!