McKeu

Top right, next to your profile is the "Customizer" switch. There you can set it.
EDIT: I will be a dick and mark my own answer as best answer, just to get this out of the open requests, since I doubt it will be changed on website level. 😄

That is hairworks hair. First you need to get your install from basic hook5 to extended, though. Otherwise it won't work.

That is hairworks hair. First you need to get your install from basic hook5 to extended, though. Otherwise it won't work.

You are running hook5 basic, still. Those menus only exist in hook5 extended.
You need to install Hook5 extended correctly. You will notice, when the "BASIC VERSION" thingy goes away.

Probably because your first attempt went wrong. You can delete the one in the klub17 folder. It needs to be in binaries only.

It's not 15 MB, it just forwards to a megalink. The whole Installation stuff should be around 1.4 GB.
There will be folders for updates as well. ONLY unpack and use "p" (not q, not r, not o or any other, just p)
Hook5 we can deal with afterwards.
This is the best and proven way to do the install:
 
1. Install Game
2. Install Latest Update P
3. Install Starter Content (Overwrite if asked)
4. Install Additional All in One Content (Overwrite if Asked)
5. Install Hook 5 Extended (Overwrite if Asked)

I had the same issue. I simply installed some H5 cum textures.
If you want to keep it simple, use these ones. They work like a charm for me (I used the 60% variant):
 

I simply ended up doing the following:
I went into the mountain oasis activemod folder, renamed the _level_definition.txt to .old, and copied the file from a hook5 room I knew was day in there (I chose the pool remake for that).
So all the info required is in that file. Could probably play around with that, but that seems time consuming. 
Why reinvent the wheel and make shit more complicated? 🙂
P.S.: You might want to copy / paste the includes from the original _level_definition file into the new one. Otherwise you cannot turn on/off the candles and stuff like that.
Depending on the file you used, you might end up with random crap in the F4 menu, though. While this method works for mountain oasis, it might not work well with other rooms. So best approach is probably to simply compare both files and figure out what exact settings are responsible for the environment lighting (Probably the whole [environment] and [sun_light] sections)  and then copy/paste into the original file, save it as an extra copy (so you keep the old one, too)
I, for example, had a rogue pool mirror floating around, which I could simply turn off in F4, though. You can also simply delete all the unwanted stuff from the end of the level definition file.