gm_shadowgreen no HDR problem

I exported the hl2_shadowgreen map from gmod to do an upcoming project, but I get an error saying that the map doesn’t have any HDR. When it loads, the entire map is washed out with a blinding light. It looks really ugly since the map is mostly dark with lighting coming from the ceiling openings. I tried inputting MAT_fullbright 0 into the console, it works, but is there a quick permanent solution?

I think this goes into the Mapping section man