Yes, it sounds contradictory, but this is the "curse" of language - its inherently dualistic - all we can talk about are things and pointing at something that is not-a-thing (not part of the world of things) is an awkward task. It is prone to sound contradictory...
To answer your question: Yes, light (in the way we conventionally use the word), is a thing.
Here is a rule of thumb: As long as you can find an opposite to something it is a thing (eg the opposite of light is dark) - if it doesn't have an opposite it is not-a-thing.
As such, all we can talk about are things - but we can point at "no-things" (like "consciousness" or "infinity"), but we do this using language which (unfortunately) objectifies the non objective.
Sure, you can use "phenomena" for light or sound, but it doesn't change what I said above.
