The Light Stalk consists of a reddish-brown stalk around four feet tall, with a small bulb on top that shines mostly bright yellow, but also green, purple or white. Whenever approached, it shakes rapidly, dims its light, and shrinks back.
In Half-Life: Alyx, Light Stalks can be found as part of Xen flora within the Quarantine Zone. The stalks appear static but can move in a segmented way when touched by the player.
Behind the scenes[]
The Light Stalk model can be found in the playable Half-Life 2 Beta files. It was to be seen at least in the sewers under the Combine Factories, as seen in the map "d1_garage_02_03.vmf".[1]