What is the trigger incident in the story Anthem?

In the story "Anthem" by Ayn Rand, the trigger incident occurs when the protagonist, Equality 7-2521, discovers a hidden tunnel from the Unmentionable Times and finds a forgotten lightbulb. This revelation ignites his curiOSity and desire for knowledge, leading him to explore individualism and ultimately challenge the collectivist society that suppresses personal freedom and innovation. This moment sets him on a path toward self-discovery and rebellion against the established norms.