I think the rule is geography-specific. For the Brits, you cut out "A range of" and you will get it correct because you are talking about the light lunches and not the range. For Americans, you cut out the prepositional phrase to check for correctness.
I think that is the lesson in this thread.
Forgive me, but that's not actually the case. Even in British English,
range is a singular noun referring to the selection, and the prepositional phrase is the correct thing to cut out to check.
The difference between the cultures about "team" or "committee" as collective nouns is a side-issue. "Range" does not fall into that category.
In both American and British English, the correct phrasing is "A range of light lunches is available."