Solarbeam?

[mattgcn]

Sure, it makes sense to be light, but Grass needs it. What we need for Grass is an equivelent, but one that would still make sense for all old SolarBeam learners to learn, and even working the same.

Or keep it Grass and make a light counterpart.

[Super Cuddles]

It really depends on the pokemon that learns solarbeam. For all fire pokemon that learns solarbeam (houndoom, rapidash and entei), a grass type hyperbeam is definitely a plus since it counters 3 of fire's weaknesses. Making solarbeam the light type attack means they can only rely on hidden power grass. For the majority of grass pokemon though, a light type solarbeam means supereffective against dragon, which is a definite plus.

[mattgcn]

But a grass one gives STAB.

Think of names that relate to Grass and Light.

Chlorobeam?

EDIT: I vote Grass unless a suitable Grass version is recreated.

[Jade]

Stay Grass.

[Super Cuddles]

I say change to light, it just makes more sense that way. We can make a new grass hyperbeam, but it doesn't neccissarily have to fit with any fire types that previously learn the grass type solarbeam, it might hinder houndoom, rapidash and entei, but they are just 3 pokemon. Or we can make the elemental hyperbeams from FR/LG learnable to more pokemon, maybe a naturally learnt move even.