That should work just fine. The light requirements of green algae are nearly identical to those of higher plants, so what's good for one is good for the other.
Besides light, algae also require a nitrogen source (ammonia is best, but nitrites and nitrates also work), CO2, and certain other nutrients such as phosphates, potassium, etc. If you really want to provide lots of algae, consider setting up an "algae farm". This can be as simple as a bucket with a clamp light on it, in which you put water, rocks, a starter rock with algae, and an airstone. Add tank water and/or a small amount of a nitrogen heavy fertilizer periodically. Switch out algae-covered rocks from the farm with grazed-over rocks from the tank. I have used this sort of setup to feed tadpoles.
One issue to consider with lava rocks is the possibility of the sharp edges damaging the mouths of grazing fish. Smoother stones may be better.
