Light-triggered night light

/*
  03 — Light-triggered night light
  Board: NodeMCU V3 ESP8266 development board.  Parts: photoresistor, relay module, 10 kΩ resistor.

  Wiring:
    Photoresistor: one leg -> 3V3, other leg -> A0 AND -> 10 kΩ -> GND
                   (a voltage divider: more light = higher reading)
    Relay module:  VCC -> VIN (5 V), GND -> GND, IN -> D1
                   Low-level trigger: the pin must go LOW to switch the relay ON.
    Lamp: through the relay's COM and NO contacts. Low-voltage lamps only
          on the bench; anything mains needs an electrician-grade enclosure.

  The delay before switching stops a passing shadow flicking the lamp.
*/

const int LDR_PIN   = A0;
const int RELAY_PIN = D1;

const int DARK_BELOW    = 300;   // pick by watching the Serial Monitor in your room
const int LIGHT_ABOVE   = 450;   // higher than DARK_BELOW = hysteresis, no chatter
const unsigned long HOLD_MS = 3000;  // must stay dark/light this long before switching

bool lampOn = false;
unsigned long since = 0;
bool pendingDark = false;

void setup() {
  Serial.begin(115200);
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, HIGH);   // HIGH = relay OFF on a low-level-trigger module
}

void loop() {
  int light = analogRead(LDR_PIN);           // 0..1023 on the ESP8266
  bool wantOn = lampOn ? (light < LIGHT_ABOVE) : (light < DARK_BELOW);

  if (wantOn != pendingDark) { pendingDark = wantOn; since = millis(); }
  if (wantOn != lampOn && millis() - since > HOLD_MS) {
    lampOn = wantOn;
    digitalWrite(RELAY_PIN, lampOn ? LOW : HIGH);
    Serial.println(lampOn ? "Lamp ON" : "Lamp OFF");
  }

  Serial.print("light="); Serial.print(light);
  Serial.println(lampOn ? "  lamp on" : "  lamp off");
  delay(200);
}