In this episode, Professor Rob Lucas talks with Prof Lane Brown from Washington State University, USA, about the third type of photoreceptor in the human eye: intrinsically photosensitive retinal ganglion cells (ipRGCs). Together, they explore what these remarkable cells do, why they matter, and the scientific journey—full of surprises and persistence—that led to their discovery. And make sure to listen until the end for some unexpected rock‑climbing stories!