When you flick the lights on and off it will trigger. Arduino with a photo-resistor.

double_tap_light.ino

// DOUBLE TAP LIGHT 0.1

unsigned long off_timer = 18000;

int power = 3;
int sensor = 5;

int threshold = 190;
unsigned long loop_count = 0;
int sense_val = 0;
int sense_0 = 0;
int sense_1 = 0;
int diff = 0;
int diff2 = 0;
int event_count = 0;
unsigned long event_timeout = 2000000002;
unsigned long light_timeout = 2000000002;
boolean light_status = false;

void setup() {
  
  pinMode(power, OUTPUT);
  Serial.begin(9600);
  
}

void loop() {
  
  sense_val = analogRead(sensor);
  //Serial.println(sense_val);

  diff = abs(sense_val - sense_0);
  diff2 = abs(sense_val - sense_1);

  if (diff > threshold || diff2 > threshold) {
    // Event: light was turned on or off
    if ( event_count > 0 ) {
      // ITS A DOUBLE TAP
      if ( light_status == false ) {
        digitalWrite(power, HIGH);
        light_status = true;
      }
      else{
        digitalWrite(power, LOW);
        light_status = false;
      }
      delay(3000);
      //digitalWrite(power, LOW);
      event_count = 0;
      light_timeout = loop_count + off_timer;
    }
    
    event_count++;
    
    event_timeout = loop_count + 20;
    
    delay(50);
    sense_val = analogRead(sensor);
    sense_0 = sense_val;
    sense_1 = sense_val;
  }

  if ( loop_count > event_timeout ) {
    // there were no subsequent light change after the first. Reset event_count.
    event_count = 0;
    event_timeout = 2000000002;
  }


  if ( loop_count % 2 == 0 ) {
    sense_0 = sense_val;
  }
  else {
    sense_1 = sense_val;
  }

  if ( loop_count > light_timeout ) {
    digitalWrite(power, LOW);
    light_status = false;
    light_timeout = 2000000002;
    delay(3000);
    sense_val = analogRead(sensor);
    sense_0 = sense_val;
    sense_1 = sense_val;
  }
  
  if ( loop_count > 2000000000 ) {
    // don't exceed the max size of an unsigned long
    loop_count = 0;
  }
  loop_count++;
  delay(50);
  
}