As I've said several times, Source does not support ambient light very well, meaning that light that bounces off a surface does not strike another surface at all other than somewhat when the map is compiled but map lighting is different yet. Making a dynamic time system is more or less out of the scope of it to do decently and have it look consistently good. So
@Murtsley we have the best with what we can realistically imo. One other slight issue that may afflict some people over other is custom monitor settings, I've noticed in several tests that my monitor seems to display things brighter than some others so I can see in the dark a bit better than someone else.
I digress so back to the point...
The main issue is that if we make lights inside buildings more intense while it would be good at night, during the day it would be blindingly bright. So there's hardly any good solution to this, I understand that it may be a bit dark in some places at night, but unfortunately there's no real good solution to this with using an engine that was developed well over a decade ago. If we simply had one time of day and had no use for a day/night cycle then sure making a map that looks amazing wouldn't be hard (and the "dim" headlights wouldn't be an issue) but I think we can all agree that the day cycle is a good thing even if it has some adverse effects.
@talia nagisan The lights you're talking about are more similar to that of the ones used in headlights, however even they have a certain brightness they can obtain while trying to dim the global lighting down to make it feel like night. Avoiding it to be like an old movie where you can tell it's clearly filmed in the day and then effects added to make it appear to be night which looks meh at best. Map lights (the ones in rooms and streetlights) however are baked onto the map at the time of map compilation so they have a certain range of settings and can not be adjusted after the map is ready to use, so we can't adjust those very well (if at all) unlike in more modern game engines.