I'm not for certain, but I'd say:
Illuminating the hallway with an eerie glow, a GHOST emerges from a nearby wall.
Or some such. You shouldn't need to identify it as a special effect, but you probably should put it all caps, so effects people will spot it. They'll know what to do with ghost, I'd imagine.
PS - just found this at ScriptLinks - Use camera directions (ANGLE ON, CLOSE UP) either rarely or not at all.
Don't include special effects.Here is a link to the site:
http://members.shaw.ca/any-word/format.htm#Dialogue