Volumetric lighting

Volumetric lighting, also known shorthand as "God rays", is a lighting technique meant to simulate light bouncing off fog or dust particles in the air, such as a warehouse or foggy beach. It makes the player see beams of light shining from the sun or other light sources. Currently, the only Valve-made software running on Source that supports Volumetric Lighting is Source Filmmaker, however some third-party engines incorporate volumetric lighting into env_projectedtexture. If the game you are making maps for doesn't support volumetric lighting, you can use some workarounds seen here.

Most versions of Source 2 have support for Volumetric lighting by default

Media

Volumetric lighting in Source Filmmaker

Volumetric lighting in Alien Swarm Deferred

Volumetric lighting in Half Life Alyx

Native Support

Source

Game	Supports
Source 2004 Source 2006 Source 2007 Source 2009/ Source Multiplayer Source 2013 Half-Life: Source Day of Defeat: Source Half-Life 2 Half-Life 2: Episode One Half-Life 2: Episode Two Alien Swarm Alien Swarm: Reactive Drop Half-Life Deathmatch: Source Half-Life 2: Deathmatch Half-Life 2: Lost Coast Counter-Strike: Source Team Fortress 2 Portal Left 4 Dead Left 4 Dead 2 Portal 2	NO
Black Mesa	YES
Alien Swarm Deferred	YES
Source Filmmaker	YES (`env_projectedtexture`)
Strata Source	YES (`env_projectedtexture`)
Apex Legends	YES