It's LordHavoc's hmap2, which is a compiler with built-in light and vis functions. 

But maybe it does things differently from other light tools? I just had another look at the readme, and this is what it says about light:

usage: hmap2 -light [options] bspfile
Compiles lighting data in a .bsp and also makes .lit colored lighting data
Quick usage notes for entities: (place these in key/value pairs)
wait - falloff rate: 1.0 default, 0.5 = double radius, 2 = half radius
_color - red green blue, specifies color of light, example 1 0.6 0.3 is orange
_lightradius - forces light to be this radius (useful with 1/ types)
delay - light type: (x = distance of surface from light, r = radius)
0: 1-(x/r) fast, quake lighting, the default, tyrlite compatible
1: 1/(x) slow, tyrlite compatible
2: 1/(x*x) slow, realistic, tyrlite compatible
3: 1 fast, no fade, useful for sky lights, tyrlite compatible
4: sun slow, directional sunlight, uses target direction like spotlights
5: 1-x/r*x/r fast, looks like darkplaces/tenebrae lights
What the options do:
-extra antialiased lighting, takes much longer, higher quality
-extra4x4 antialiased lighting, even slower and better than -extra
-extra8x8 antialiased lighting, even slower and better than -extra4x4
-nolightvis disables use of visibility data to optimize lighting
-relight make a .lit file for an existing .bsp without modifying the .bsp
-harshshade harsh shading rather than the normal soft shading
Options from here on are incompatible with darkplaces realtime lighting mode
(it does not know if these options are used, and will require manual rtlights
editing to look good)
-intensity scales brightness of all lights
-radiusscale scales size of all lights (including 1/ types)
-defaulttype <number> sets default light type by number, see delay above
-overridetypes forces all lights to use the -defaulttype setting
-minlight raises darkest areas of the map to this light level (0-255)
-ambientlight raises all of the map by this light level (0-255)

So maybe it ignores the settings of the .map file and requires one to set sunlight via the command line?

Or is all of that stuff jut about coloured lighting? 

I use tyranns light tools combined with necros compiling gui. I can't really see a reason to use anything else. 

which I finally figured out. So I recompiled using qbsp and then I ran light, like this: ./light mapname

Once again, all my light entities work, but there's no sunlight in the map (despite my using the exact values from post 14047), and areas where I put no light entities yet are surrounded by sky brushes, are pitch black.

What am I doing wrong? 

What version of trenchbroom are you using? For me, snap to grid just reduces the grid size to pixel size. 

not just one face? 

That is the case; the entire brush is textured with sky texture. 

if you're on windows then best just using this tool -
http://shoresofnis.wordpress.com/utilities/ne_q1spcompilinggui/

Here's a mapfile I made which has the sunlight set up. As long as you're using tyranns tools it should work right -

https://www.dropbox.com/s/afzmvlm0wvs3spt/sunlight.zip 

In Worldcraft you just go Edit -> Map properies, then use the UI to change the values.

Check your .map file.

Here are the first few lines from my honey map jam map (with an example of sunlight):

{
"classname" "worldspawn"
"classname" "worldspawn"
"message" "Yellow Brick Grotto"
"_sunlight" "123"
"gravity" "800"
"sounds" "5"
"light" "12"
"_sunmangle" "40 -45 0"
"_sun_mangle" "45 -45 0"
"fog" "0.03 0.025 0.055 0.14"
"mapversion" "220"
"wad" "\program files\worldcraft\textures\skip.hlwad;\program files\worldcraft\textures\honey.hlwad"
{
( 496 0 -512 ) ( 368 0 -512 ) ( 304 -32 -512 ) CITY2_3 [ 1 0.......

Incidentally, I don't know why the worldspawn is declared twice, it just IS. Anyone? Is this an error?

Either way, if you .map file looks like that in your text editor, then something else is going on. If not, try making it like the above... 

I checked my map file as you suggested, and it turns out I had made a mistake with the _sun_mangle values. Fixed it, and now sunlight finally works.

Thank you so much, FifthElephant and RickyT23!

In response to your question, RickyT23: in TrenchBroom, when you select a brush you can add and edit properties. By default if it is a regular, non-func brush, it only lists classname, spawnflag and wad (if it's textured). Everything else (e.g. "_sunlight") you can then add manually (if you know what it is called).

worldspawn is listed only once in my map file, by the way.

Re: 14057: Thanks, Fifth, but I am on Linux. 

Bizarrely, though, I cannot open it with TrenchBroom (although I can open it in a text editor). 

It's just empty, right?

Sorry; with every consecutive post I must seem like more of an idiot. 

It's a simple box room. 

Oh, right. Just needed to rotate the camera almost completely. Yes, it's all there.

Well, as I said, with every consecutive post I must seem like more of an idiot. 

it's probably because of where the geometry is. I can't leave what I was working on there, probably going to do something special for the next jam. 

Not sure if it should go here or in the TrenchBroom thread ...

Is it possible to flip a brush/selection of brushes in TB so as to get an exact mirror image of it?

I know you can turn it around using alt + the arrow/PgUP/PgDn keys, but I guess all of that just turns the brush/selection in different directions as if it were a real 3D object. Or maybe I'm missing something and there's some magic sequence of twists and turns that produces a mirror image? 

That flips it... is that what you mean? 

ALT CTRL F flips it vertically. 

That is exactly what I mean. You both rock! :) 

When using this, even though folder preferences are in order and the tools are actually there, I get this error:

'D:\Files\Design\Quake' is not recognized as an internal or external command, operable program or batch file. Press any key to continue.

What gives? 

I haven't used that tool but I'd guess you're trying to use a path that has a space in it, and the tool is cantankerous about that.

Possible solutions if so:
- Rename the folders in the path to remove spaces.
- Put double-quotes around the path in the place where you enter it in the tool; or if the tool uses a config file and saves the path there, try editing that to add the quotes.
- Use DOS-style shortnames in the path.

You can use "dir -x" in a command prompt to see shortnames. 

Oops sorry that would be "dir /x". 

D:\Files\

what could possibly be outside this folder 

D:\NullSet 

D:\DiskSpaceRemaining