 int i_color_r = 255;
 int i_color_g = 0;
 int i_color_b = 0;
+float instrument_brightness_min = 0.5; // default brightness
+float instrument_brightness = 1;
 
 // effect color
 int e_color_r = 0;
 int e_color_g = 0;
 int e_color_b = 255;
-
-float instrument_brightness_min = 0.5; // default brightness
-float instrument_brightness = 1;
 float effect_brightness = 0;
+float effect_brightness_target = 0;
 
 int divide = 2; // LEDパターンの分割数
 float slit_position = 0.5; // 0~1 分割された区分の中のどこまでがinstrumentにするか。0だと全部effect color。1だと全部instrument color。

      if(argument.length()==1) {
        // argument is int
        divide = argument.toInt();
        Serial.print("set divide number: ");
        Serial.println(divide);
        updateLED();
      }
      else {

    }
  }
  else {

    // instrument brightness
    if(instrument_brightness_min+0.01 <= instrument_brightness) {
      instrument_brightness -= 0.01;
      updateLED();
    }

    // effect brightness
    // fade effect brightness to effect_brightness_target value
    float diff = abs(effect_brightness_target-effect_brightness);
    if(0.01<diff){
      if(effect_brightness_target < effect_brightness) {
        effect_brightness -= 0.01;
      }
      else {
        effect_brightness += 0.01;
      }
      updateLED();
    }
    else if(diff != 0.0){
      effect_brightness = effect_brightness_target;
    }
  }
}
