I'll just agree to disagree then, because there are only four main elements in Chrono Trigger. It's just the way the game works. Now if we were talking about Chrono Cross, that'd be an entirely different beast altogether.
Do note that in the Chrono Trigger DS port, that Crono's Lightning element was translated correctly to Light. The use of Sky/Heaven likely carried the "heavenly"/"holy" connotation.
There are four main elements in the game: Light, Shadow, Water, Fire. These are the resistances and weaknesses of the elemental forces in the game.
Code:
--------.---------.---------.---------.---------.
Element | Light | Shadow | Water | Fire |
--------|---------|---------|---------|---------|
Light | W | S | S | N |
--------|---------|---------|---------|---------| S = Strong.
Shadow | S | W | N | N | W = Weak.
--------|---------|---------|---------|---------| N = Normal.
Water | N | N | W | S |
--------|---------|---------|---------|---------|
Fire | N | N | S | W |
--------'---------'---------'---------'---------'
No matter wihch spell you use, even if it's Lightning or Luminaire, it will carry the Light attribute. That's how the elemental system in this game works. It is
not Chrono Cross or Final Fantasy.