If you use visible light, then one can use a phone (screen) to blink the pattern to transmit data. An LED can also be used as the sensing element, just need acc

If you use visible light, then one can use a phone (screen) to blink the pattern to transmit data. An LED can also be used as the sensing element, just need access to both anode and cathode. Charge the LED and measure the discharge time - it is dependent on light in.