Light meter: photoresistor on A0, LEDs on pins 5 to 12, on an Arduino Uno

// A light meter: the more light, the more of the eight LEDs light.
//
//   5V -> photoresistor -> A0 -> 10k resistor -> GND
//   pins 5 to 12 -> one 220 ohm resistor and one LED each -> GND
//
// The photoresistor's resistance falls as light lands on it, so A0 reads
// more in bright light. map() turns the reading, 0 to 1023, into a count of
// LEDs, 0 to 8, and the loop lights that many from pin 5 up.
//
// Drag the photoresistor's light level and watch the bar.

const int SENSOR = A0;
const int LEDS[] = {5, 6, 7, 8, 9, 10, 11, 12};
const int COUNT = 8;

int shown = -1;

void setup() {
  for (int i = 0; i < COUNT; i++) pinMode(LEDS[i], OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: light meter on A0");
}

void loop() {
  int reading = analogRead(SENSOR);
  int level = map(reading, 0, 1023, 0, COUNT + 1);
  if (level > COUNT) level = COUNT;
  for (int i = 0; i < COUNT; i++) digitalWrite(LEDS[i], i < level ? HIGH : LOW);
  if (level != shown) {
    shown = level;
    Serial.print("light ");
    Serial.print(reading);
    Serial.print(": ");
    Serial.print(level);
    Serial.println(" LEDs");
  }
  delay(50);
}