The sensors of the Infrared LED Board for RPi Camera are based on on-board photoresistors to detect the ambient light and a potentiometer to control the ambient light threshold toggling of the infrared LED.
The sensor part of the camera has two pins to power the circuit (VCC and GND) as shown in the attachement and has an operating voltage of 3.3V. Therefore, when the sensor module is powered at 3.3V, the LED will be toggled at a certain ambient light (detected by the photoresistor). You can find a lot of examples online of an IR LED controlled with a photoresistor. Here is an example.