https://forum.arduino.cc/t/easiest-way-to-slowly-ramp-led-strip/1329379

# include <Wire.h>
# include <RTClib.h>
# include <FastLED.h>

# define LED_PIN     2
# define NUM_LEDS    12
# define BRIGHTNESS  255

CRGB leds[NUM_LEDS];
RTC_DS3231 rtc;

// Time settings
int sunriseHour = 6; // Default sunrise time hour
int sunriseMinute = 0; // Default sunrise time minute
int sunsetHour = 18; // Default sunset time hour
int sunsetMinute = 0; // Default sunset time minute

unsigned long sunriseStartMillis;
unsigned long sunsetStartMillis;

bool isSunrise = false;
bool isSunset = false;

void setup() {
  Serial.begin(9600);
  FastLED.addLeds<WS2812, LED_PIN, GRB>(leds, NUM_LEDS);
  rtc.begin();

  // Set the RTC time if needed (uncomment the next line to set)
  rtc.adjust(DateTime(2024, 12, 8, 5, 59, 0));

  // Set default sunrise/sunset times if needed
  // rtc.adjust(DateTime(2023, 10, 1, 12, 0, 0)); // Set time for testing
}

void loop() {
  DateTime now = rtc.now();
  int currentHour = now.hour();
  int currentMinute = now.minute();

  // Check if it's time for sunrise or sunset
  if (currentHour == sunriseHour && currentMinute == sunriseMinute) {
    isSunrise = true;
    isSunset = false;
    sunriseStartMillis = millis();
  } else if (currentHour == sunsetHour && currentMinute == sunsetMinute) {
    isSunset = true;
    isSunrise = false;
    sunsetStartMillis = millis();
  }

  if (isSunrise) {
    performSunrise();
  } else if (isSunset) {
    performSunset();
  }

  FastLED.show();
  delay(1000); // Adjust delay as needed
}

void performSunrise() {
  unsigned long elapsed = millis() - sunriseStartMillis;
  if (elapsed < 1800000) { // 30 minutes in milliseconds
    float progress = (float)elapsed / 1800000.0;

    // Brightness from 0 to 255
    uint8_t brightness = progress * BRIGHTNESS;
    // Color transition from orange to white
    CRGB color = blend(CRGB(255, 165, 0), CRGB(255, 255, 255), brightness);

    fill_solid(leds, NUM_LEDS, color);
    FastLED.setBrightness(brightness);
  } else {
    // Maintain full brightness white after sunrise
    fill_solid(leds, NUM_LEDS, CRGB(255, 255, 255));
    FastLED.setBrightness(BRIGHTNESS);
  }
}

void performSunset() {
  unsigned long elapsed = millis() - sunsetStartMillis;
  if (elapsed < 1800000) { // 30 minutes in milliseconds
    float progress = (float)elapsed / 1800000.0;

    // Brightness from 255 to 0
    uint8_t brightness = BRIGHTNESS * (1.0 - progress);

    // Color transition from white to dark orange to magenta to blue
    CRGB color1 = CRGB(255, 255, 255);
    CRGB color2 = CRGB(255, 165, 0);
    CRGB color3 = CRGB(128, 0, 128); // Magenta
    CRGB color4 = CRGB(0, 0, 255); // Blue

    if (progress < 0.33) {
      // First third: white to dark orange
      CRGB color = blend(color1, color2, progress * 3 * 100);
      fill_solid(leds, NUM_LEDS, color);
    } else if (progress < 0.66) {
      // Second third: dark orange to magenta
      CRGB color = blend(color2, color3, (progress - 1.0 / 3.0) * 3 * 100);
      fill_solid(leds, NUM_LEDS, color);
    } else {
      // Last third: magenta to blue
      CRGB color = blend(color3, color4, (progress - 2.0 / 3.0) * 3 * 100);
      fill_solid(leds, NUM_LEDS, color);
    }

    FastLED.setBrightness(brightness);
  } else {
    // Turn off LEDs after sunset
    fill_solid(leds, NUM_LEDS, CRGB::Black);
    FastLED.setBrightness(0);
    isSunset = false;
  }
}

// Function to set the time on the RTC (call this function with new time)
void setTime(int year, int month, int day, int hour, int minute, int second) {
  rtc.adjust(DateTime(year, month, day, hour, minute, second));
}

// Functions to set sunrise and sunset times
void setSunriseTime(int hour, int minute) {
  sunriseHour = hour;
  sunriseMinute = minute;
}

void setSunsetTime(int hour, int minute) {
  sunsetHour = hour;
  sunsetMinute = minute;
}