Cones escape saturation and reopen CNG channels in bright light. Current responses from a Gnat1^−/− cone (A) and a Gnat1^−/−;Rv^–/-;Gcaps^−/− cone (B) to a brief, saturating flash (∼5,000 P*/flash) followed by exposure to steady light. The trace in A is a single exposure of >40 s at 110,000 P*/s. The trace in B gives average photocurrent responses from two exposures of 405-nm light bleaching 30,000 ± 7,000 P*/s for 20 s. 5 s after the steady light was turned on, flashes of increasing strength were delivered to the cone (1,800 ± 100 to 29,000 ± 1,000 P*/flash). The dashed line illustrates the initial peak–current response. (C) Average photocurrent responses to brief flashes (arrows) were measured in the Gnat1^−/− cone from A during dark conditions (black traces) and during a steady background (blue traces). (D) Similar backgrounds were presented to Gnat1^−/− cones (n = 5) and Gnat1^−/−; Rv^−/−;Gcaps^−/− cones (n = 5). The peak current responses of the flashes were normalized to the maximal response in the presence of the background and plotted against the number of pigment molecules bleached by the flashes (P*). Data were fit with Eq. 1 to obtain values of I_1/2. The sensitivity of Gnat1^−/− cones was determined to be 700 ± 13 P* in the dark (black) and 9,400 ± 1,500 P* during steady illumination (blue). The sensitivity of Gnat1^−/−;Rv^−/−;Gcaps^−/− cones was 410 ± 16 P* in the dark (gray) and 470 ± 13 P* during steady illumination (red). The principal effect of background light on the triple knockouts was to decrease the number of open channels. Error bars represent SEM.