Systems and techniques for providing data to a user in the form of perceived light signals caused by transcutaneous stimulation of the user's optic nerve. User output data, suitably representing data collected, generated, or processed by a data processing device, is used to generate user output data. The user output data is converted to representations corresponding to light signals, and control functions are performed to cause generation of electrical impulses which, when applied to the skin of a user, stimulate the optic nerve of the user so as to cause the user to perceive the light signals.