3 W power LED on pin 13, on an Arduino Uno

// A 3 W power LED, blinking on pin 13.
//
//   MOSFET module TRIG -> pin 13   GND -> GND
//   module VIN+ -> 5V   VIN- -> GND
//   module OUT+ -> 4.7 ohm -> LED +   LED - -> module OUT-
//
// A power LED wants hundreds of milliamps, far more than the 20 mA a pin can
// give, so the pin only drives the gate of a MOSFET and the MOSFET switches
// the LED's current straight from the 5 V supply. The 4.7 ohm resistor sets
// that current: about (5 - 3.4) / 4.7, or 340 mA, half the LED's rating,
// which is how a small 3 W module runs it from 5 V.

// The MOSFET's gate is on pin 13. Instead of delay(), the sketch keeps the
// time it last switched and flips the gate once a second has passed, so
// loop() is free for anything else a lamp might need, like a button.

const int GATE_PIN = 13;
const unsigned long PERIOD_MS = 1000;

bool lit = true;
unsigned long switchedAt = 0;

void setup() {
  pinMode(GATE_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: 3 W LED on pin 13, through a MOSFET");
  digitalWrite(GATE_PIN, HIGH);
  switchedAt = millis();
}

void loop() {
  if (millis() - switchedAt < PERIOD_MS) return;
  switchedAt += PERIOD_MS;
  lit = !lit;
  digitalWrite(GATE_PIN, lit ? HIGH : LOW);
  Serial.println(lit ? "gate high: the LED draws about 340 mA" : "gate low: the LED is dark");
}