A head mounted display system configured to project variable levels of blue light to an eye of a user, the display system comprising: a frame configured to be wearable on a head of the user; a display configured to project at least blue light into the eye of the user and to modify an intensity of the blue light relative to an intensity of non-blue light; a camera configured to capture images of the eye while the display projects light into the eye; and a hardware processor (70, 72, 210) programmed to: instruct the camera to capture a first image of the eye while the display projects light at a first ratio of intensity of blue light to non-blue light into the eye, the first ratio being greater than zero; instruct the display to change the first ratio to a second ratio of the intensity of blue light to non-blue light; instruct the camera to capture a second image of the eye while the display projects light at the second ratio of intensity of blue light to non-blue light into the eye, the second ratio being greater than zero and different from the first ratio; determine that a change in a pupil parameter between the second image and the first image matches a biometric characteristic of a human individual; and based on the determination that the change in the pupil parameter between the second image and the first image matches the biometric characteristic of the human individual, determine an identity of the human individual. a frame configured to be wearable on a head of the user; a display configured to project at least blue light into the eye of the user and to modify an intensity of the blue light relative to an intensity of non-blue light; a camera configured to capture images of the eye while the display projects light into the eye; and a hardware processor (70, 72, 210) programmed to: instruct the camera to capture a first image of the eye while the display projects light at a first ratio of intensity of blue light to non-blue light into the eye, the first ratio being greater than zero; instruct the display to change the first ratio to a second ratio of the intensity of blue light to non-blue light; instruct the camera to capture a second image of the eye while the display projects light at the second ratio of intensity of blue light to non-blue light into the eye, the second ratio being greater than zero and different from the first ratio; determine that a change in a pupil parameter between the second image and the first image matches a biometric characteristic of a human individual; and based on the determination that the change in the pupil parameter between the second image and the first image matches the biometric characteristic of the human individual, determine an identity of the human individual. instruct the camera to capture a first image of the eye while the display projects light at a first ratio of intensity of blue light to non-blue light into the eye, the first ratio being greater than zero; instruct the display to change the first ratio to a second ratio of the intensity of blue light to non-blue light; instruct the camera to capture a second image of the eye while the display projects light at the second ratio of intensity of blue light to non-blue light into the eye, the second ratio being greater than zero and different from the first ratio; determine that a change in a pupil parameter between the second image and the first image matches a biometric characteristic of a human individual; and based on the determination that the change in the pupil parameter between the second image and the first image matches the biometric characteristic of the human individual, determine an identity of the human individual.