A new study quietly repositions the bedroom as a site of cardiovascular consequence, finding that even faint light during sleep may alter the structure and function of the heart. For generations, darkness at rest was understood intuitively; now science is beginning to articulate what that intuition protected. The research invites us to reconsider how many small, ambient intrusions — the glow of a clock, the bleed of a streetlamp — accumulate into biological cost over a lifetime of nights.