Many people experience a period of reduced alertness in the afternoon, what researchers call the post-lunch dip.

WSJ: The Secret to An Afternoon Energy Boost: Red Lighting

But from the time I got interested in this over a four- or five-year period, I'd go to lunch or dinner with people and they'd say, 'What are you working on?

WSJ: He Drills for Answers | Robert M. Edsel | Cultural Conversation by Joanne Kaufman