There's only a few situations I can see this being worth the cost (not just quanta, but also creature health). Most obvious is when you have a lot of creatures out, but you have to wait until then to play it, meaning a dead card in your hand for a long time.
Second, you can play this card for a little edge to finish someone off, even if you have only a handful of creatures out, every point of damage makes a difference. It only works for rainbows or light decks, though, with a cost that high. Rainbow decks would spam this card mercilessly, and they'd have the light quanta to use it - an OP scenario, because every rainbow would have to use it in order to face another rainbow.
The most common deck I can think of involving Light right now is RoL Fractal-Hope. If, as the card says, halving rounds down, it'll kill creatures with 1 health. The way the game mechanic works, if a spell drops a creature's health to zero, it dies IMMEDIATELY. It won't act at all like a Spark, it'll just die before it attacks. Whereas if you change the rounding to UP, you could never kill a creature with this spell, and critters with 1 health would have nothing to lose. This would be an ESSENTIAL card in any RoL/Hope deck, usable repeatedly and very OP since you're dealing with a full field of Rays. Bye-bye Light Dragons.
Very problematic card. Every situation I can think of makes this card either pointless or essential - either UP or OP. Full-field type decks could crank out 46 extra damage for EVERY one of these played, but for non-swarming decks, the cost is prohibitive.
