5. Ambient Light Level

Measure relative ambient brightness with an LDR. This is not a calibrated lux meter; it provides a clear dark-to-bright comparison.

Level: Beginner · Time: 25 minutes

Parts and wiring

ESP32 DevKit V1, LDR, and 10 kΩ resistor

Build this divider:

3V3 → LDR → measurement point (GPIO 34) → 10 kΩ → GND

Complete sketch


#include <PxServ.h>
 
const char* WIFI_SSID = "your_wifi_ssid";
const char* WIFI_PASSWORD = "your_wifi_password";
const char* PXSERV_API_KEY = "your_pxserv_api_key";
const int LDR_PIN = 34;
 
PxServ client(PXSERV_API_KEY);
 
void setup() {
  Serial.begin(115200);
  analogReadResolution(12);
  PxServ::connectWifi(WIFI_SSID, WIFI_PASSWORD);
}
 
void loop() {
  long total = 0;
  for (int i = 0; i < 10; i++) {
    total += analogRead(LDR_PIN);
    delay(10);
  }
 
  int rawValue = total / 10;
  int lightPercent = constrain(map(rawValue, 0, 4095, 0, 100), 0, 100);
 
  client.setData("light/raw", String(rawValue));
  client.setData("light/percent", String(lightPercent));
  Serial.print("Light: ");
  Serial.println(lightPercent);
  delay(5000);
}

Test and calibration

Cover the LDR, then illuminate it with a phone flashlight. The reported percentage should change clearly. For a more useful local scale, record the raw dark and bright values and use them as the map() endpoints.