Light has been used to reveal almost everything we know about the universe because that is what enables us to see the cosmos.
In the 2-part 2013 documentary "Light and Dark", British professor Jim Al-Khalili investigates how we have used light to explore our universe, with a specific focus on the last 30 years within which we have pushed back the boundaries of what is "visible". For we now know that things we can see with our eyes in the universe only make up about 1% of it. But rather than this being a restriction we have developed new techniques to observe things which seem to be hidden in the dark making our voyage of discovery evermore intriguing and exciting, yielding increasing fundamental knowledge.
Like other documentaries by Jim exploring foundational topics about the makeup of reality, this two-part series is split into two rather appropriately name sections "light" and "dark".