yes I raised the specular color from l_glas shader to 1.5 but therefore decreased the decay from 80 to 15. at first I tried too using hdri. but the shader with alone spotlights creates enough color to leave out additional reflection supporters.

I´ll do some testing now and show how different settings affect the final image. what I can already say is that pushing the specular value above 1 is tricky cause 1.5 is even more than enough. it blows polys which are facing towards the camera. I guess a range of +-0.1 is proper.