Emissive brightness with greyscale

Hey,
I just spend some time to figure out if it’s possible to get different brightness with an emissive material for different parts of an object.
The green should be way brighter than the whiteish part.
Here are some of my tries.
Generic emissive material:

Some experimenting:

adding invert since the green is way darker, but just got white out of it:

This is the mask i was using: