void spiral2() {
  static uint8_t stripIndex = 0;
  static uint8_t dotIndex = 0;

  // first, dim all LEDs, every time
  for (int x = 0; x < NUM_STRIPS; x++) {
    for (int i = 0; i < NUM_LEDS_PER_STRIP; i++) {
      leds [x][i].fadeToBlackBy(64);
    }
  }

  // then, once per X milliseconds, light up the next LED
  EVERY_N_MILLISECONDS(1000) {
    leds[stripIndex][dotIndex] = CHSV( gHue + random8(64), 200, 255);

    // move to the next strip
    stripIndex++;

    // wrap back to the first strip
    if (stripIndex >= NUM_STRIPS) {
      stripIndex = 0;
    }

    // move to the next LED
    dotIndex++;

    // wrap back to the first LED
    if (dotIndex >= NUM_LEDS_PER_STRIP) {
      dotIndex = 0;
    }
  }
}