A laboratory has been established for measurement of charges in pupil diameter in response to a variety of visual stimulus presentations. A recently redesigned pupilometer permits the determination of visual stimulus luminances required for criterion changes in pupil diameter (e.g., 0.1 mm.), or pupil diameter for steady state conditions of stimulation. Spatial-temporal modulation of a grating pattern (180 degree phase shift) has been employed to provide a stimulus of constant average luminance. Grating frequency was selected so that the pattern is not discriminable by rods but can be discriminated by cones. A spatial response curve based on the transient pupillary response was found to correspond to the V-lambda function with a peak at 555 nm. The peak of a curve based on the steady state pupil diameter was found to be at 495 nm, and has been attributed to rods.