Open your .scenerio file in Guerilla. Now, on the top, there is a pull-down menu that says "Solo." Click it, and select Multiplayer instead.
Now, where it says Sky in the same file, find and select a .sky file.
Once done, save.
Then. open your map in sapien, and press the ~ button on your keyboard.
Type in:
Radiosity_Quality 0
press enter
Radiosity_Start
Now, wait for the numbers to go down to 0.
Once done, press the ~ button again, and type in:
Radiosity_Save
Tada! The lightmaps appear!
Halo uses an advanced light module called "Radiosity." It takes the light properties of a skybox to create realistic light around your map, and it takes the light properties of certain shaders that have radiosity power and color enabled.
If the number counter doesn't start when you type in Radiosity_Start, then you didn't follow the HEK tut on adding a skybox material to your geometry.