On the night of April 18, 1775, a signal was sent from the steeple of Old North Church in Boston to Paul Revere, who was 1.80 mi away: “One if by land, two if by sea.” At what minimum separation did the sexton have to set the lanterns for Revere to receive the correct message about the approaching British? Assume that the patriot’s pupils had a diameter of 4.00 mm at night and that the lantern light had a predominant wavelength of 580 nm.