byte val = 5;
byte lightPwm = 0;
void setup() {
  pinMode(3, INPUT);
  pinMode(7, OUTPUT);
}
void loop() {
  if (digitalRead(3)) {
    analogWrite(7, lightPwm);
    lightPwm = lightPwm + val;
    if ( (lightPwm == 0) || (lightPwm == 1000))
      val = -val;
     delay(50);
  }
  else {
    digitalWrite(7, HIGH);
    delay(100);
    digitalWrite(7, LOW);
    delay(100);
  }
}