From Valve Developer Community
This entity is also available as light_environment for the Source engine.
This entity is also available as light_environment (Source 2) for the Source engine.
- Overrides the pitch value in Angles, even if left at 0, so it needs to be specified. Contrary to Angles, the rotation of this pitch is measured counter-clockwise from the horizontal, so that 90 is straight up, while -90 is straight down. (It's simply the negative of a normal pitch value.)
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- Color and brightness of direct Sunlight.
- Pitch Yaw Roll (Y Z X)
- This entity's orientation in the world. Pitch is rotation around the Y axis, yaw is the rotation around the Z axis, roll is the rotation around the X axis.