写一段Arduino代码，实现用按键开关依次切换ws2812灯带的九种模式，九种模式均为白光，区别为照度和闪烁频率

好的，下面是实现你要求的Arduino代码，使用了Adafruit公司的neopixel库：

#include <Adafruit_NeoPixel.h>

#define LED_PIN 6
#define NUM_LEDS 30

Adafruit_NeoPixel strip(NUM_LEDS, LED_PIN, NEO_GRB + NEO_KHZ800);

int mode = 0;

void setup() {
  strip.begin();
  strip.show(); // Set all pixel colors to 'off'
  pinMode(2, INPUT_PULLUP);
}

void loop() {
  if (digitalRead(2) == LOW) {
    mode++;
    if (mode > 8) {
      mode = 0;
    }
    delay(100);
  }

  switch (mode) {
    case 0:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 255, 255, 255);
      }
      strip.show();
      delay(500);
      break;

    case 1:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 127, 127, 127);
      }
      strip.show();
      delay(500);
      break;

    case 2:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 63, 63, 63);
      }
      strip.show();
      delay(500);
      break;

    case 3:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 31, 31, 31);
      }
      strip.show();
      delay(500);
      break;

    case 4:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 15, 15, 15);
      }
      strip.show();
      delay(500);
      break;

    case 5:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 7, 7, 7);
      }
      strip.show();
      delay(500);
      break;

    case 6:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 3, 3, 3);
      }
      strip.show();
      delay(500);
      break;

    case 7:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 1, 1, 1);
      }
      strip.show();
      delay(500);
      break;

    case 8:
      for (int i = 0; i < NUM_LEDS; i++) {
        strip.setPixelColor(i, 255, 255, 255);
      }
      strip.show();
      delay(50);
      strip.setBrightness(50);
      strip.show();
      delay(50);
      strip.setBrightness(255);
      strip.show();
      delay(50);
      break;
  }
}

这段代码使用按键开关切换九种模式，每种模式都是白光，区别在于照度和闪烁频率。当按下按键时，模式会依次切换，直到最后一个模式后重新回到第一个模式。