The env_glow entity is much like the env_sprite in that it places a sprite within the map. The only differences seem to be that the env_glow does not animate its sprite, it cannot be triggered, and that it lacks some of the options that the env_sprite has.
Render FX (renderfx) - Gives the sprite certain visual effects depending on Render Mode.
Normal (0) - No visual effects.
Slow Pulse (1) - Sprite slowly pulses with transparency. Faint.
Fast Pulse (2) - Sprite quickly pulses with transparency. Faint.
Fast Wide Pulse (4) - Sprite quickly pulses 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) - Sprite flickers in and out of visibility.
Fast Flicker (13) - Sprite quickly flickers in and out of visibility.
Constant Glow (14) - If Render Mode is Glow, the sprite will remain the same size and visible at any distance.
Distort (15) - Sprite has a slight fast pulsing of transparency.
Hologram (Distort + fade) (16) - Sprite has a slight fast pulsing of transparency. Fades out 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.
Color (1) - Allows sprite to become transparent. (Counter-intuitively, is the only Render Mode that is not affected by FX Color.)
Texture (2) - Allows sprite to become transparent.
Glow (3) - Removes background of sprite. Sprite will appear larger and become more faint with distance. Allows sprite to become transparent.
Solid (4) - Allows sprite to become transparent.
Additive (5) - Removes background of sprite. Allows sprite to become transparent.
FX Amount (1 - 255) (renderamt) - In all but "Normal" Render Mode, alters how transparent the sprite is. Scales from 0 (invisible) to 255 (solid, normal).
FX Color (R G B) (rendercolor) - Alters the colour of the sprite. Will have no effect if R, G and B are all equal.
Name (targetname) - Name is a general attribute used to identify entities.
Sprite Name (model) - This defines which sprite file will be displayed by the entity. This accepts an input of the form "path/filename.spr" (starting from the root folder). (Example: "sprites/tele1.spr").
Scale (scale) - Sets the scale of the sprite, in the form of a size multiplier.
It is recommended that you use an env_sprite entity instead of env_glow, as it can do everything the env_glow entity does and more.