So what should I do to use it? What process do I stick this thing on? 

What about worldspawn's "_sunlight_color" key? I'm using tyrutils v0.15 qbsp, vis and light, getting only bland white sunlight. It seems to ignore that key. I tried 64 192 255 and it's still white. I'm on Worldcraft 3.3, but that shouldn't matter. What am I'm missing? 

Sorry, I'm mapping for Quake 1. Here's light.exe output:

---- light / TyrUtils v0.15 ----
running with 4 threads
BSP is version 29
Colored light entities detected: .lit output enabled.
4 entities read, 0 are lights.
0....1....2....3....4....5....6....7....8....9...
Lighting Completed.

lightdatasize: 1989
0 switchable light styles
Writing BSP version 29
0.0 seconds elapsed

The level shows sunlight, but it's always white, no matter how I set _sunlight_color 

Make sure to copy the both the .lit and .bsp to your maps directory, if you're compiling in a different directory.
Does your engine have .lit support? Most do, except the original winquake/glquake. 

Guys, think I pulled the trigger too soon. For some reason, when I ran light outside Worldcraft it worked. Sunlight is blue now. My bad. 

In order to eliminate unnecessary files, I was deleting the .lit
Gotta copy the .lit along with the .bsp 

I noticed light.txt doc doesn't say anything about this key, but I see you talking about it sometimes.

Are you compiling your lights using tyrann's light.exe? Anyone setting _sunlight2 and/or _sunlight2_color? 

I made a fork of tyrutils with various new features, _sunlight2 is only in that. I haven't made a proper release, so it's just buried in various forum threads and hard to find :-(

The latest snapshot is from may 1:
https://www.dropbox.com/sh/1q5giu2leyvvhk0/AAA0UCacYD-tgVpElMSpf5Awa?dl=0 

Does this version have _sunlight2? Because it's doing nothing for my map. Do you happen to have some example map showing its effect? My map has a central yard where sunlight hits. I was counting on _sunlight2 to cast some sunlight on the "outside" walls as well. 

Take this test .MAP:

https://drive.google.com/open?id=0B3Ww0W8WFfq7bFB6NGFhT2t1R0E&authuser=0

It has:
"_sunlight" "300"
"_sun_mangle" "180 -90 0"
"_sunlight_color" "255 64 64"
"_sunlight2" "200"
"_sunlight2_color" "64 64 255"

I was expecting to see a red square in the middle and all the other walls in a blue tint, but only the red square appears. What am I doing wrong? 

Yep, that build should do _sunlight2.
Only "sky" textures emit sunlight, just texture the outer box with "sky1" or any sky texture and I think that will fix it 

ignore that, didn't notice that you already had a sky textured skylight.

I think what's happening is, the _sunlight2 is working, it's just really dim because there it's a fairly narrow opening to the sky. A _sunlight2 value of 200 will light up a surface to a value of 200 only if it has an unobstructed 180-degree view of the sky. Try setting it to 1000 and you'll get some blue light on the walls. (this will make outdoor areas with more of a view of the sky too bright, though) 

Really? I thought _sunlight2 worked more like an "ambient" minimum light to the "outside" faces, ones facing a sky textured face in any angle (maybe inside the same portalled volume?). I mean, there is ambient light for all surfaces and _sunlight2 for "outside" surfs. Did I get it wrong?

If the surface must have an unobstructed 180 degree view of the sky, the floor in this test level shouldn't be affected by _sunlight2? 

Been seeing this kind of explanation:

"�_sunlight2′ and �_sunlight_color2′ to make a sort of outdoor minlight. The light utility creates an array of minlight casting suns in a circle and sort of floods outdoor areas."

I don't get what this "array of suns in a circle" look like. Not sure about the effect I should get as well. 

bjptools has a _sunlight2 that works like you describe.

maybe I should have named my version something other than _sunlight2 because the effect is quite different. I wanted to not just do a simple minlight based on sky visibility.

Here's a screenshot: https://runeofearthmagic.wordpress.com/2015/02/22/yoghurt-sunlight/

The soft shadows on the main, pink, sunlight is a different feature (_sunlight_penumbra). You can see the difference in _sunlight2 in the shadow of the taller tower: in the top (bjptools) screenshot, the shadowed area is just an even shade of gray. In the bottom screenshot (my modified _sunlight2) the gray areas have more shading depending on how much a given spot can see the sky. 

You were right. I set _sunlight2 to 2k to start noticing some change. A value of 20k turned affected surfaces into washed white.

Also, I need ambient occlusion, so I'll keep using your code :P

Thanks!! 

Here's my first attempt using your light tool. This is supposed to be moon lit, night time.

First, the fullbright image:
https://drive.google.com/open?id=0B3Ww0W8WFfq7cGUtN2pvdUZsWnc&authuser=0

Now, ericw's magic:
https://drive.google.com/open?id=0B3Ww0W8WFfq7Y05fZU5VcHZGNjg&authuser=0

Not sure if it's gonna be night. I'm gonna light the rooms and then try daylight / night.

I used here:
worldspawn
_dirt 1
_sunlight 350
_sunlight_color 64 184 255
_sunlight2 5000
_sunlight2_color 64 184 255
_sunlight_penumbra 4
_sun_mangle 180 -90

Lighted with -extra4 -anglescale 0

The level is very vertical. There's a floor below, with ugly shadows. I had to help with two point lights scaled 0.1, value 50, no falloff, same color as the sun.

Still working... 

That's a good looking scene! What texture set are you using? 

These are all my own :) I intend to release them along with the level. It's intended to be 1x1 deathmatch, but I see Qonquer potential on it. We'll see. 

Reminds me of piranesi counter strike map, the original, not any source release. 

I guess _sunlight2 5000 may cause problems with overly bright lighting if you have any rooms with a bigger area of sky visible.

Maybe I will look at some kind of exponential exposure thing for _sunlight2 so that rooms with a narrow strip of sky like yours can light up a decent amount, without washing out fully outdoor areas, like gb's city I posted earlier. 

... but is not my only problem. Take a look:

https://drive.google.com/open?id=0B3Ww0W8WFfq7UHAxamdRcUF2YUU

This is what happens when I set ambient light to 50: there is the brown texture color where black shadow should be (look where the crosshair is). There is "ambient light" where _sunlight2 doesn't reach (casting shadow).

For now, I just gave up on ambient light. But how to solve it properly? Or is it nonsense?

I know there is _minlight for brush entities. But should I turn a massive amount of brushes into some entity? What are the cons? 

the brown is probably grey, it just looks brown compared to the blue lighting around it.

Can you specify R G B for the ambient instead of just one number? 

I thought there'd be a worldspawn key for minlight color, but looks like it's only available on brush entities (_mincolor). Will add that to the todo list. 

There is "external" ambiance, lit by moon, but there will be also rooms lit by orange lamps. I couldn't pick just one _mincolor.

@metlslime I think it's not gray, it's just the texture pixels lit by worldspawn "ambient light"

Anyways, I turned that whole wall into a func_wall and set _minlight to 50 and _mincolor to the same blue moonlight:

https://drive.google.com/open?id=0B3Ww0W8WFfq7WG5tVzhfMkl0anM

Looks like mincolor lit _sunlight2 shadows. But there's still unlit faces (facing down) and I don't know why. They are part of the same func_wall.