[Arduino Uno R3] LED brightness with digitalWrite.

You can control LED brightness with digitalWrite.
Normally, LED brightness with digitalWrite is regular.
If you want to control LED brightness, use delay function.

The time that LED is on is long, people will see the LED seems brighter.
Like following.

The right LED is brighter, because the time that LED is on is longer than the time that LED is off.
The left LED is more dark.

Following is code.
// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int led = 13;

// the setup routine runs once when you press reset:
void setup() {
  // initialize the digital pin as an output.
  pinMode(led, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(9);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1);               // wait for a second
}