The phrase "proverbial light" refers to a well-known and commonly used metaphorical idea or concept. It often represents wisdom, knowledge, understanding, or clarity that one gains, similar to a light illuminating the darkness. Full definition
And that's when the proverbial light bulb went off for the inveterately affable denim king: «I thought: Wouldn't it be great to offer genetic testing as an optional program, free of charge, to our employees?» (fortune.com)
He laid out the example above and the proverbial light bulb went off in my head. (thedividendlife.com)
Hope is the proverbial light at the end of the tunnel, beckoning us with some sort of promise that our lot will improve. (educationworld.com)