User blog comment:Evillalobosm/Cruciatus Curse Spell Color/@comment-3095064-20120507210557

I do not believe the curse is supposed to have a jet of light at all. Checking the book, there appears to be no mention of any light during this scene in the book, nor any of the other instances I checked (though I did not check them all). I think the red light might be an invention of the films, if a reference to a light in the books cannot be found.