The xen_hair entity places a model of a plantlight into the map. A plantlight is a little decorative xen model that retracts while the player is in close proximity to it, and re-emerges after a few seconds when the player moves away. With certain render attributes, the plantlight will have a glow sprite attached to its bulb.
Render FX (renderfx) - Gives the model and the sprite certain visual effects depending on Render Mode.
Normal (0) - No visual effects.
Slow Pulse (1) - Model and sprite slowly pulse with transparency. Faint.
Fast Pulse (2) - Model and sprite quickly pulse with transparency. Faint.
Slow Wide Pulse (3) - Model and sprite slowly pulse with transparency. Strong.
Fast Wide Pulse (4) - Model and sprite quickly pulse with transparency. Strong.
Slow Fade Away (5) - Seemingly unused.
Fast Fade Away (6) - Seemingly unused.
Slow Become Solid (7) - Seemingly unused.
Fast Become Solid (8) - Seemingly unused.
Slow Strobe (9) - A very slow strobe effect between visible and invisible.
Fast Strobe (10) - A medium strobe effect between visible and invisible.
Faster Strobe (11) - A very fast strobe effect between visible and invisible.
Slow Flicker (13) - Model and sprite flicker in and out of visibility.
Fast Flicker (13) - Model and sprite quickly flicker in and out of visibility.
Constant Glow (14) - The sprite will remain the same size and visible at any distance.
Distort (15) - Model and sprite have a slight fast pulsing of transparency, and the model occasionally translocates slightly. (Translocation visible with "Normal" Render Mode.)
Hologram (Distort + fade) (16) - Model and sprite have a slight fast pulsing of transparency, and the model occasionally translocates slightly. (Translocation visible with "Normal" Render Mode.) Model will fade with distance.
Render Mode (rendermode) - Allows special rendering modes to be applied to the given entity.
Normal (0) - Standard rendering. Render FX and FX Amount will generally have no effect on the model.
Color (1) - Allows model to become transparent.
Texture (2) - Allows model to become transparent.
Glow (3) - Allows model to become transparent.
Solid (4) - Allows model to become transparent.
Additive (5) - Gives the model a white glow. Allows model to become transparent.
FX Amount (1 - 255) (renderamt) - Alters how transparent the sprite is, and in all but "Normal" Render Mode, alters how transparent the model is. Scales from 0 (invisible) to 255 (solid, normal).
FX Color (R G B) (rendercolour) - Alters the colour of the sprite. Will have no effect if R, G and B are all equal.
Target (target) - When the plantlight retracts, it will trigger the entity specified in Target to turn off. When the plantlight emerges, it will trigger the entity specified in Target to turn on.
Name (targetname) - Name is a general attribute used to identify entities.
Pitch Yaw Roll (Y Z X) (angles) - Sets the pitch, yaw and roll angles of the model.
This entity has no flags.
The intended use of this entity is to have it target a light entity in the same spot, so as to give the effect that the plantlight is emitting light while it is not retracted.
The plantlight is also perfectly capable of triggering any other kind of entity, however. If you want to rig it up to an env_explosion to act as some kind of proximity mine, go right ahead. Worth noting, however, is that if it is triggering an entity without on/off states, such as an env_explosion, it will be activated both when the plantlight retracts and re-emerges.
The sprite on the bulb of the plantlight will always be treated as though it has the Glow Render Mode, regardless of what you set that attribute to on the xen_plantlight.
When using the strobe and flicker Render FXs, the sprite will not disappear along with the plantlight. The sprite will instead move to the base of the plantlight and remain visible until the plantlight reappears, where it will move back to its normal location. This is likely not intended, as the effect is not particularly appealing.
The area the player must be in to make the plantlight retract seems to be a 164 unit square around the origin of the plantlight. The area extends downwards 2 units from the origin, and 34 units upwards. (This is noticeably shorter than the plant itself while extended.)