How to wake up ESP8266 with light change?
The deep sleep functionality of the ESP8266 is managed by tying pin 16 to the RESET pin and when you call the deep sleep function you pass the number of microseonds you want to sleep. Then the microcontroller sets pin 16 high and goes to sleep. After the specified amount of time the pin 16 goes low causing the ESP8266 to reset. Please see the "low power solutions" pdf from Espressif for the API details, including some application notes.

So, your plan of connecting to pin 16 is not going to work exactly. You need a circuit that detects that pin 16 is high and then generates a low pulse on RST when your condition triggers. Without knowing more details about your circuit and exact triggering condition or is hard to provide a detailed answer.