What defines the darkness of a map (night or day)?

[DisneyOnAcid]

Hi, I've been googling this for a long while but haven't found the answer. I was wondering, where is the lighting/darkness of a map defined? I mean what makes the map appear dark like it's at night as opposed to daytime? Is it something that can be changed by editing shaders or the .bsp file's entities? Or does it need to be defined before compiling the map?
I'm not a map maker but I want to try to make small changes to the game's original maps and I'm interested in how this works.

 

 

Thanks!

[mrwonko]

There's basically a big texture containing the light information called a "lightmap", which is calculated during compilation from light entities that are not themselves included, making the process irreversible. It's conceivable to edit the lightmap directly in theory, I believe it's too much work for anybody to have ever bothered since without a proper editor (which there isn't) it's nigh impossible to tell which part of the texture corresponds to which part of the map.

[Futuza]

Usually if you want a "night" version of a map you just need to compile two different versions a day and night version and then just have two different bsps for each one.  It's possible someone might be able to work out some sort of magic swapping thing between multiple lightmap points if you wanted time lapsing day-night cycles, but that'd take some weird hacking above my level of understanding.

[ensiform]

It's not very easily feasible in the current engine or renderer. @Darth

[ladiszlai]

The simplest way is add the "ambient" key to your worldspawn entity. 

[Asgarath83]

I am not a lightmap expert, so basically i use the light ambient and also some rgb filter for the map. also

minlight and midlight and a skybox with sun \ moon helps.