A method and device for radiating light used to capture an iris are provided. The device for radiating light to capture an iris of a user includes a lens unit including a lens array of arranged lenses, a light source configured to radiate light beams into the iris of the user via the arranged lenses by emitting the light beams toward the arranged lenses, and a controller configured to change positions of the arranged lenses based on a distance between the device and the iris, in which the lens array is positioned between the light source and the iris.