What differentiates an abstract noun with a concrete noun?

I think you are best asking this question of the person who first taught you this terminology. It's not an official term like noun or verb. That said, some words clearly describe actual things you can touch, hear, and see (desk, dog, apple) and others describe intangible concepts (love, employment contract, marriage, tax rate). When my kids and I play 20 Questions, we add a category that covers these things along with TV shows, songs, emotions and other intangibles. Definitely for advanced players :-).

In Object Oriented Programming, concrete classes describe things that can actually exist (truck, employee, purchase order, savings account, square) and abstract classes describe "umbrella concepts" that are more category than object (vehicle, business entity, transaction, bank account, shape). I ask my students to imagine opening "just a bank account - not a savings account, not a chequing account, not a retirement account, just an account." It can't be done. Abstract classes can't be instantiated. Only concrete ones can. Now, does this have anything to do with the distinction someone made to you? And how does sunlight fit into this?

Nouns can all be catagorized as concrete or abstract. It is a linguistic construct. Concrete nouns can be sensed, or more simply put have atomic structure or form. However, language is complex and variable so a specific song or dance is considered concrete due to its specific pattern of tones or movements, whereas time, despite its patterns, is considered abstract. Abstract nouns are typically emotions, philosophies, ideas, or concepts.

Abstract nouns are basically used for representation of ideas, qualities, states, something that cannot be perceived by the senses of touch, sight, hearing, smell and taste. For example, honesty, happiness, sadness are abstract nouns. Concrete nouns, on the other hand, can be perceived by our five senses. Mostly, the concrete nouns refer to something that we can touch and so they are also named as material nouns. For example, noise, sunlight (in your case), table, chair, etc. I hope that helped.

'Concrete nouns can be perceived by our senses'.

This cannot be correct. Our senses do not perceive the noun 'corn'. Our senses perceive corn -- that entity to which the noun 'corn' refers. (Or to the extent that our sense of language perceives nouns, it perceives all nouns.)

When I was taught this concrete/abstract distinction in middle school, at that time I thought this was foolish for counterexamples came to mind immediately. 'Electron' is an entity that cannot be (so to speak) 'sensed', but it is not (so to speak) an 'idea'.

I did not have the words to describe my attitude at the time, but now I describe it this way: The books (and teachers) were, no doubt unwittingly, trying to teach us a (dubious) ontology under the guise of teaching us grammar.

If you can show me how nouns that refer to things that can be 'perceived by the senses' have some unique morphological features (say), or some other properties that control how they are used in a sentence, then I will accept them as valid grammatical categories. Otherwise the distinction makes no more sense than distinguishing 'fooish' nouns as nouns that refer to round things, and 'barish' as nouns that are not 'fooish'.

Thus 'apple' is a fooish noun, while 'banana' is a barish noun.

These might be useful categories for a fruit packing factory, and might be of pragmatic interest to those programming a natural language interface for use in a packing factory, but they make no linguistic sense.

I may certainly be wrong, and would love to be corrected if I am.

[Edited to add:]

I will somewhat correct my previous claim. A noun might be abstract if it affords a certain kind of morphology suggested my these examples:

'paradigm' -> 'paradigmatic', and 'universe' -> 'universal'.

In contrast, paradigmatic concrete nouns like 'corn' and 'rock' (and the original poster's 'sunlight') afford no such morphological change.

This, though, is a fairly arcane distinction to teach middle school students.