The Light cantrip has this restriction:
"You can only have one light spell active at any one time. If you cast this spell while another casting is still in effect, the previous casting is dispelled. If you make this spell permanent (through permanency or a similar effect), it does not count against this limit."
Does this limit apply if you are a multi-classed caster casting Light as a cleric and then as a wizard, for example?
The strictest ready would seem to say that only one Light spell could be active at a time. I , however, would rule that if you have it as a cantrip and an orison, then cast away! In that case you could have two Light spells going. It is not a game breaker so I would not worry too much about it.
I don't see anything separate about having it on two class lists, but personally I'd allow it one active light spell for as many times as you actually memorize it (spontaneous casters need not apply).
So if you were a Clr/Wiz, you could have as many as 8 memorized and active. I think that goes with the spirit of the spell. That's RAM (Rules According to Me) ;)
Thanks! Interesting ideas!