Almost all corals feed from sources other than light whether it is SPS, LPS, Leather, etc.
While it is true that light for most SPS corals in particular can provide them with 100% of their daily energy needs however building of the coral tissue from light alone for growth is slowed or weakened.
Other than photosynthesis and depending on the particular SPS species, other elements they feed on are things like carbohydrates, amino acids, and urea from the water column.
Believe it or not some corals even up take sediments that have a many different elements from decaying organisms, fish feces, etc.
Another source from the water column is plankton. In particular phytoplankton, and zooplankton. Artemia is also another source.
So yes SPS need more than just light for optimum growth and they are already up taking from the water column in your tank plenty of what is mentioned above, whether your tank has all the elements needed in enough quantities is a different story.