const int NbrLEDs = 8;
int latchPin = 5;
int clockPin = 6;
int dataPin = 4;
const int photocellPin = A0;
int ledLevel = 0;
byte states[8] = {B10000000,B11000000,B11100000,B11110000,B11111000,B11111100,B11111110,B11111111};
int sensorValue = 0;

 void updateShiftRegister(byte leds){
   digitalWrite(latchPin, LOW);
   shiftOut(dataPin, clockPin, LSBFIRST, leds);
   digitalWrite(latchPin, HIGH);
}

void setup() {
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
  digitalWrite(latchPin, HIGH);
}

void loop() {
   sensorValue = analogRead(photocellPin);
   ledLevel = map(sensorValue, 0, 1023, 0, NbrLEDs);
   updateShiftRegister(states[ledLevel]);
}