The IR light from the eye-tracking illuminators is invisible to the eye, but sometimes visible to digital cameras. Digital cameras often use infrared blockers, but cheaper digital cameras and camera phones have less effective filters and can 'see' intense near-infrared light, appearing as a bright purple-white color.
The IEC 62471 standard for products using LED tests for all possible eye damage, i.e., exposure of the cornea and the image on the retina, both peak power and average powers.
Yes. Tobii eye tracking systems use near-infrared illumination to create reflections on the eyes that can be tracked with high accuracy. Read more