Automatic mood light

A night light with a personality. When the room is bright, the light stays off. As it gets darker it glows warm orange, and in full darkness it fades to a calm blue. The colours change smoothly, so there are no sudden jumps.

What you need

• UNO R3 board and USB cable
• Photoresistor module (45-in-1 Sensor Kit)
• RGB LED module (45-in-1 Sensor Kit)
• 3 resistors, 220 Ω
• Breadboard and jumper wires

Wiring

Build it step by step

1. Place both modules and the three resistors on the breadboard as in the diagram.
2. Connect 5V and GND to the breadboard rails.
3. Upload the code and open the Serial Monitor at 9600 baud.
4. Note the light value in a bright room and when you cover the sensor. Set BRIGHT and DARK to those numbers.
5. Upload again and slowly cover the sensor to watch the colours change.

The code

const int SENSOR_PIN = A0;
const int RED_PIN = 9;
const int GREEN_PIN = 10;
const int BLUE_PIN = 11;

// Set these from your own Serial Monitor readings
int BRIGHT = 200;   // reading in a bright room
int DARK = 800;     // reading with the sensor covered

float level = 0;    // smoothed darkness, 0 = bright, 1 = dark

void setColor(int r, int g, int b) {
  analogWrite(RED_PIN, r);
  analogWrite(GREEN_PIN, g);
  analogWrite(BLUE_PIN, b);
}

void setup() {
  Serial.begin(9600);
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);
}

void loop() {
  int light = analogRead(SENSOR_PIN);
  Serial.println(light);

  // 0 when bright, 1 when dark (works whichever way your module counts)
  float target = (float)(light - BRIGHT) / (DARK - BRIGHT);
  target = constrain(target, 0.0, 1.0);

  // Move slowly towards the target so the colour changes smoothly
  level = level + (target - level) * 0.05;

  if (level < 0.2) {
    setColor(0, 0, 0);                         // bright room: off
  } else if (level < 0.6) {
    float f = (level - 0.2) / 0.4;             // dusk: warm orange, getting brighter
    setColor(255 * f, 80 * f, 0);
  } else {
    float f = (level - 0.6) / 0.4;             // dark: orange fades to blue
    setColor(255 * (1 - f), 80 * (1 - f), 200 * f);
  }
  delay(30);
}

How it works

The sketch turns the light reading into a "darkness level" between 0 and 1, using your own bright and dark readings so it works with any module. Instead of jumping straight to the new level, it moves 5% of the way each time, which makes the colours fade smoothly. Three ranges then decide the colour: off, warm orange at dusk, and a blend from orange to blue in the dark.

Make it your own

• Pick your own colours for dusk and darkness.
• Make the light "breathe" slowly in the dark by changing the brightness over time.
• Put the light in a jar or behind paper to soften the glow.

Troubleshooting

• The light never turns on: check your BRIGHT and DARK numbers against the Serial Monitor.
• A colour is missing: check that colour's resistor and wire.
• Colours are inverted: your RGB LED may be common anode. Connect the common pin to 5V and use 255 - value in setColor().

Learn the basics first

New to these parts? These lessons explain them step by step: Build an automatic night light and Mix colours with the RGB LED module.