r_ambient
This variable controls the amount of ambient lighting on the map. When this variable is increased the map will become brighter and all walls and objects will be rendered in a lighter color. It was removed in QWCL and has been re-introduced in this client, however it can only be used when the server is running with cheats enabled (for example "qwsv -cheats"), because it could be used as a cheat by making it easier to see players in dark corners when no fullbright skins are used.