androidLCD和键盘 背光亮度设置

 亮度设置
 应用设计
1.1 设置进度条范围
背光设置是在：设置->声音和显示->亮度，通过进度条来设置的。

文件：packages/apps/Settings/src/com/android/settings/BrightnessPreference.java

private static final int MINIMUM_BACKLIGHT = android.os.Power.BRIGHTNESS_DIM + 10;

private static final int MAXIMUM_BACKLIGHT = android.os.Power.BRIGHTNESS_ON;

mSeekBar.setMax(MAXIMUM_BACKLIGHT - MINIMUM_BACKLIGHT);

设置进度条的范围，BRIGHTNESS_DIM = 20  BRIGHTNESS_ON=255，它们的定义在：

frameworks/base/core/java/android/os/Power.java

1.2 设置亮度
文件：packages/apps/Settings/src/com/android/settings/BrightnessPreference.java

public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {

       setMode(isChecked ? Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC

                : Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);

        if (!isChecked) {

            setBrightness(mSeekBar.getProgress() + MINIMUM_BACKLIGHT);

        }

    }

private void setBrightness(int brightness) {

        try {

            IPowerManager power = IPowerManager.Stub.asInterface(

                    ServiceManager.getService("power"));

            if (power != null) {

                power.setBacklightBrightness(brightness);

            }

        } catch (RemoteException doe) {

           

        }       

}

由以上代码可知，brightness的范围是：20~255;代码通过服务管理器(ServiceManager)获得power服务，然后通过power服务设置亮度。

power.setBacklightBrightness的定义在：

rameworks/base/core/java/android/os/IPowerManager.aidl.java

frameworks/base/core/java/android/os/PowerManager.java

2， Power服务
文件：frameworks/base/core/java/android/os/Power.java

/**

     * Brightness value for dim backlight

     */

    public static final int BRIGHTNESS_DIM = 20;

 

    /**

     * Brightness value for fully on

     */

public static final int BRIGHTNESS_ON = 255;

文件：frameworks/base/core/java/android/os/PowerManager.java

/**

     * sets the brightness of the backlights (screen, keyboard, button).

     *

     * @param brightness value from 0 to 255

     *

     * {@hide}

     */

    public void setBacklightBrightness(int brightness)

    {

        try {

            mService.setBacklightBrightness(brightness);

        } catch (RemoteException e) {

        }

}

电源管理器(powermager)将brightness转给电源服务，该服务位置如下：

文件：frameworks/base/services/java/com/android/server/PowerManagerService.java

public void setBacklightBrightness(int brightness) {

        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.DEVICE_POWER, null);

        // Don't let applications turn the screen all the way off

        brightness = Math.max(brightness, Power.BRIGHTNESS_DIM);

        mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BACKLIGHT, brightness,

                HardwareService.BRIGHTNESS_MODE_USER);

        mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_KEYBOARD,

            (mKeyboardVisible ? brightness : 0), HardwareService.BRIGHTNESS_MODE_USER);

        mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BUTTONS, brightness,

            HardwareService.BRIGHTNESS_MODE_USER);

        long identity = Binder.clearCallingIdentity();

        try {

            mBatteryStats.noteScreenBrightness(brightness);

        } catch (RemoteException e) {

            Log.w(TAG, "RemoteException calling noteScreenBrightness on BatteryStatsService", e);

        } finally {

            Binder.restoreCallingIdentity(identity);

        }

 

        // update our animation state

        if (ANIMATE_SCREEN_LIGHTS) {

            mScreenBrightness.curValue = brightness;

            mScreenBrightness.animating = false;

            mScreenBrightness.targetValue = -1;

        }

        if (ANIMATE_KEYBOARD_LIGHTS) {

            mKeyboardBrightness.curValue = brightness;

            mKeyboardBrightness.animating = false;

            mKeyboardBrightness.targetValue = -1;

        }

        if (ANIMATE_BUTTON_LIGHTS) {

            mButtonBrightness.curValue = brightness;

            mButtonBrightness.animating = false;

            mButtonBrightness.targetValue = -1;

        }

    }

由以上代码可知，同时设置了背光、键盘、按钮的亮度。mHardware 是硬件服务，通过该服务调用底层与设备打交道的C/C++代码，setLightBrightness_UNCHECKED原型如下：

文件：frameworks/base/services/java/com/android/server/HardwareService.java

void setLightBrightness_UNCHECKED(int light, int brightness, int brightnessMode) {

        int b = brightness & 0x000000ff;

        b = 0xff000000 | (b << 16) | (b << 8) | b;

        setLight_native(mNativePointer, light, b, LIGHT_FLASH_NONE, 0, 0, brightnessMode);

    }

参数说明：int light 表示类型，选项如下：

static final int LIGHT_ID_BACKLIGHT = 0;

    static final int LIGHT_ID_KEYBOARD = 1;

    static final int LIGHT_ID_BUTTONS = 2;

    static final int LIGHT_ID_BATTERY = 3;

    static final int LIGHT_ID_NOTIFICATIONS = 4;

static final int LIGHT_ID_ATTENTION = 5;

int brightness 表示亮度值

int brightnessMode 表示亮度的控制模式，选项如下：

/**

     * Light brightness is managed by a user setting.

     */

    static final int BRIGHTNESS_MODE_USER = 0;

 

    /**

     * Light brightness is managed by a light sensor.

     */

static final int BRIGHTNESS_MODE_SENSOR = 1;

由代码：

int b = brightness & 0x000000ff;

        b = 0xff000000 | (b << 16) | (b << 8) | b;

可知，亮度值在此进行了修改，即亮度值的格式变成：FFRRGGBB，FF是没有的，RR、GG、BB分别是256色的红绿蓝，并且红绿蓝的值都是一样的亮度值。

3 硬件调用
3.1获取硬件
文件：frameworks/base/services/jni/com_android_server_HardwareService.cpp

enum {

    LIGHT_INDEX_BACKLIGHT = 0,

    LIGHT_INDEX_KEYBOARD = 1,

    LIGHT_INDEX_BUTTONS = 2,

    LIGHT_INDEX_BATTERY = 3,

    LIGHT_INDEX_NOTIFICATIONS = 4,

    LIGHT_INDEX_ATTENTION = 5,

    LIGHT_COUNT

};

 

#define LIGHTS_HARDWARE_MODULE_ID "lights"

 

static jint init_native(JNIEnv *env, jobject clazz)

{

    int err;

    hw_module_t* module;

    Devices* devices;

   

    devices = (Devices*)malloc(sizeof(Devices));

 

    err = hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);

    if (err == 0) {

        devices->lights[LIGHT_INDEX_BACKLIGHT]

                = get_device(module, LIGHT_ID_BACKLIGHT);

        devices->lights[LIGHT_INDEX_KEYBOARD]

                = get_device(module, LIGHT_ID_KEYBOARD);

        devices->lights[LIGHT_INDEX_BUTTONS]

                = get_device(module, LIGHT_ID_BUTTONS);

        devices->lights[LIGHT_INDEX_BATTERY]

                = get_device(module, LIGHT_ID_BATTERY);

        devices->lights[LIGHT_INDEX_NOTIFICATIONS]

                = get_device(module, LIGHT_ID_NOTIFICATIONS);

        devices->lights[LIGHT_INDEX_ATTENTION]

                = get_device(module, LIGHT_ID_ATTENTION);

    } else {

        memset(devices, 0, sizeof(Devices));

    }

 

    return (jint)devices;

}

用hw_get_module获取ID为LIGHTS_HARDWARE_MODULE_ID的硬件模块，该模块含有6个不同类型的亮度控制。

hw_get_module 的实现原理，如下：

文件：hardware/libhardware/Hardware.c

#define HAL_LIBRARY_PATH "/system/lib/hw"

static const char *variant_keys[] = {

    "ro.hardware",  /* This goes first so that it can pick up a different

                       file on the emulator. */

    "ro.product.board",

    "ro.board.platform",

    "ro.arch"

};

 

static const int HAL_VARIANT_KEYS_COUNT =

    (sizeof(variant_keys)/sizeof(variant_keys[0]));

int hw_get_module(const char *id, const struct hw_module_t **module)

{

    int status;

    int i;

    const struct hw_module_t *hmi = NULL;

    char prop[PATH_MAX];

    char path[PATH_MAX];

 

    /*

     * Here we rely on the fact that calling dlopen multiple times on

     * the same .so will simply increment a refcount (and not load

     * a new copy of the library).

     * We also assume that dlopen() is thread-safe.

     */

 

    /* Loop through the configuration variants looking for a module */

    for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {

        if (i < HAL_VARIANT_KEYS_COUNT) {

            if (property_get(variant_keys[i], prop, NULL) == 0) {

                continue;

            }

            snprintf(path, sizeof(path), "%s/%s.%s.so",

                    HAL_LIBRARY_PATH, id, prop);

        } else {

            snprintf(path, sizeof(path), "%s/%s.default.so",

                    HAL_LIBRARY_PATH, id);

        }

        if (access(path, R_OK)) {

            continue;

        }

        /* we found a library matching this id/variant */

        break;

    }

 

    status = -ENOENT;

    if (i < HAL_VARIANT_KEYS_COUNT+1) {

        /* load the module, if this fails, we're doomed, and we should not try

         * to load a different variant. */

        status = load(id, path, module);

    }

 

    return status;

}

property_get(variant_keys[i], prop, NULL) 会按如下顺序去获取如下变量所对应的值，然后返回给prop：

"ro.hardware",  /* This goes first so that it can pick up a different

                       file on the emulator. */

    "ro.product.board",

    "ro.board.platform",

"ro.arch"

它们对应的变量为：

"ro.product.board=$TARGET_BOOTLOADER_BOARD_NAME"

"ro.board.platform=$TARGET_BOARD_PLATFORM"

如vendor/htc/dream-open/BoardConfig.mk里定义的TARGET_BOARD_PLATFORM := msm7k，则prop返回” msm7k ”，所以path = /system/lib/hw/lights. msm7k.so，也就是说要获取的硬件模块为lights. msm7k.so。

3.2调用硬件

setLight_native对应的jni C/C++代码是：

文件：frameworks/base/services/jni/com_android_server_HardwareService.cpp

static void setLight_native(JNIEnv *env, jobject clazz, int ptr,

        int light, int colorARGB, int flashMode, int onMS, int offMS, int brightnessMode)

{

    Devices* devices = (Devices*)ptr;

    light_state_t state;

 

    if (light < 0 || light >= LIGHT_COUNT || devices->lights[light] == NULL) {

        return ;

    }

 

    memset(&state, 0, sizeof(light_state_t));

    state.color = colorARGB;

    state.flashMode = flashMode;

    state.flashOnMS = onMS;

    state.flashOffMS = offMS;

    state.brightnessMode = brightnessMode;

 

    devices->lights[light]->set_light(devices->lights[light], &state);

}

通过light标识找到对应的light设备，然后再设置亮度。

3.3 硬件原型
msm7k的lights对应的硬件原型是在：hardware/msm7k/liblights

文件：hardware/msm7k/liblights/Android.mk

LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw

LOCAL_MODULE := lights.$(TARGET_BOARD_PLATFORM)

 

也就是生成模块：/system/lib/hw/lights. msm7k.so

 

文件：hardware/msm7k/liblights/lights.c

/** Open a new instance of a lights device using name */

static int open_lights(const struct hw_module_t* module, char const* name,

        struct hw_device_t** device)

{

    int (*set_light)(struct light_device_t* dev,

            struct light_state_t const* state);

 

    if (0 == strcmp(LIGHT_ID_BACKLIGHT, name)) {

        set_light = set_light_backlight;

    }

    else if (0 == strcmp(LIGHT_ID_KEYBOARD, name)) {

        set_light = set_light_keyboard;

    }

    else if (0 == strcmp(LIGHT_ID_BUTTONS, name)) {

        set_light = set_light_buttons;

    }

    else if (0 == strcmp(LIGHT_ID_BATTERY, name)) {

        set_light = set_light_battery;

    }

    else if (0 == strcmp(LIGHT_ID_NOTIFICATIONS, name)) {

        set_light = set_light_notifications;

    }

    else if (0 == strcmp(LIGHT_ID_ATTENTION, name)) {

        set_light = set_light_attention;

    }

    else {

        return -EINVAL;

    }

 

    pthread_once(&g_init, init_globals);

 

    struct light_device_t *dev = malloc(sizeof(struct light_device_t));

    memset(dev, 0, sizeof(*dev));

 

    dev->common.tag = HARDWARE_DEVICE_TAG;

    dev->common.version = 0;

    dev->common.module = (struct hw_module_t*)module;

    dev->common.close = (int (*)(struct hw_device_t*))close_lights;

    dev->set_light = set_light;

 

    *device = (struct hw_device_t*)dev;

    return 0;

}

static struct hw_module_methods_t lights_module_methods = {

    .open =  open_lights,

};

以上代码对应的是：

devices->lights[LIGHT_INDEX_BACKLIGHT]

                = get_device(module, LIGHT_ID_BACKLIGHT);

        devices->lights[LIGHT_INDEX_KEYBOARD]

                = get_device(module, LIGHT_ID_KEYBOARD);

        devices->lights[LIGHT_INDEX_BUTTONS]

                = get_device(module, LIGHT_ID_BUTTONS);

        devices->lights[LIGHT_INDEX_BATTERY]

                = get_device(module, LIGHT_ID_BATTERY);

        devices->lights[LIGHT_INDEX_NOTIFICATIONS]

                = get_device(module, LIGHT_ID_NOTIFICATIONS);

        devices->lights[LIGHT_INDEX_ATTENTION]

                = get_device(module, LIGHT_ID_ATTENTION);

也就是说，对不同的亮度设置给予了不同的设置函数。

举例，背光设置，背光对应的代码如下：

char const*const LCD_FILE

        = "/sys/class/leds/lcd-backlight/brightness";

static int

rgb_to_brightness(struct light_state_t const* state)

{

    int color = state->color & 0x00ffffff;

    return ((77*((color>>16)&0x00ff))

            + (150*((color>>8)&0x00ff)) + (29*(color&0x00ff))) >> 8;

}

static int

set_light_backlight(struct light_device_t* dev,

        struct light_state_t const* state)

{

    int err = 0;

    int brightness = rgb_to_brightness(state);

    pthread_mutex_lock(&g_lock);

    g_backlight = brightness;

    err = write_int(LCD_FILE, brightness);

    if (g_haveTrackballLight) {

        handle_trackball_light_locked(dev);

    }

    pthread_mutex_unlock(&g_lock);

    return err;

}

也就是往文件/sys/class/leds/lcd-backlight/brightness写入亮度值，然后驱动会根据该文件更改背光的亮度。LCD_FILE的路径根据实际情况更改，同时需要在init.rc 修改其权限，使其可写rgb_to_brightness也根据实际更改，比如要直接亮度值控制，那只要获取r,g,b其中的一个值就行了，如：

static int

rgb_to_brightness(struct light_state_t const* state)

{

    int color = state->color & 0x000000ff;

    return color;

}

 

4，led类驱动

4.1，驱动创建leds类，系统启动时执行leds_init在目录/sys/class/创建子目录leds

 kernel/drivers/leds/Led-class.c

 

static int __init leds_init(void)
{
 leds_class = class_create(THIS_MODULE, "leds");
 if (IS_ERR(leds_class))
  return PTR_ERR(leds_class);
 leds_class->suspend = led_suspend;
 leds_class->resume = led_resume;
 return 0;
}

 

4.2，led_classdev_register，调用这个函数就在目录/sys/class/leds创建子目录led_cdev->name和属性文件brightness

对brightness文件写就执行led_brightness_store，对brightness文件读就执行led_brightness_show，为下面的lcd，led注册做好准备

 kernel/drivers/leds/Led-class.c

static ssize_t led_brightness_show(struct device *dev,
  struct device_attribute *attr, char *buf)
{
 struct led_classdev *led_cdev = dev_get_drvdata(dev);

 /* no lock needed for this */
 led_update_brightness(led_cdev);

 return sprintf(buf, "%u/n", led_cdev->brightness);
}

static ssize_t led_brightness_store(struct device *dev,
  struct device_attribute *attr, const char *buf, size_t size)
{
 struct led_classdev *led_cdev = dev_get_drvdata(dev);
 ssize_t ret = -EINVAL;
 char *after;
 unsigned long state = simple_strtoul(buf, &after, 10);
 size_t count = after - buf;

 if (*after && isspace(*after))
  count++;

 if (count == size) {
  ret = count;

  if (state == LED_OFF)
   led_trigger_remove(led_cdev);
  led_set_brightness(led_cdev, state);
 }

 return ret;
}

static DEVICE_ATTR(brightness, 0644, led_brightness_show, led_brightness_store);

/**
 * led_classdev_register - register a new object of led_classdev class.
 * @parent: The device to register.
 * @led_cdev: the led_classdev structure for this device.
 */
int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
{
 int rc;

 led_cdev->dev = device_create(leds_class, parent, 0, led_cdev,
          "%s", led_cdev->name);
 if (IS_ERR(led_cdev->dev))
  return PTR_ERR(led_cdev->dev);

 /* register the attributes */
 rc = device_create_file(led_cdev->dev, &dev_attr_brightness);
 if (rc)
  goto err_out;

#ifdef CONFIG_LEDS_TRIGGERS
 init_rwsem(&led_cdev->trigger_lock);
#endif
 /* add to the list of leds */
 down_write(&leds_list_lock);
 list_add_tail(&led_cdev->node, &leds_list);
 up_write(&leds_list_lock);

 led_update_brightness(led_cdev);

#ifdef CONFIG_LEDS_TRIGGERS
 rc = device_create_file(led_cdev->dev, &dev_attr_trigger);
 if (rc)
  goto err_out_led_list;

 led_trigger_set_default(led_cdev);
#endif

 printk(KERN_INFO "Registered led device: %s/n",
   led_cdev->name);

 return 0;

#ifdef CONFIG_LEDS_TRIGGERS
err_out_led_list:
 device_remove_file(led_cdev->dev, &dev_attr_brightness);
 list_del(&led_cdev->node);
#endif
err_out:
 device_unregister(led_cdev->dev);
 return rc;
}
EXPORT_SYMBOL_GPL(led_classdev_register);

 

4.3，lcd驱动调用led_classdev_register，在目录/sys/class/leds创建子目录lcd-backlight和属性文件brightness 

kernel/drivers/video/msm/Msm_fb.c

static int lcd_backlight_registered;

static void msm_fb_set_bl_brightness(struct led_classdev *led_cdev,
     enum led_brightness value)
{
 struct msm_fb_data_type *mfd = dev_get_drvdata(led_cdev->dev->parent);
 int bl_lvl;

 if (value > MAX_BACKLIGHT_BRIGHTNESS)
  value = MAX_BACKLIGHT_BRIGHTNESS;

 /* This maps android backlight level 0 to 255 into
    driver backlight level 0 to bl_max with rounding */
 bl_lvl = (2 * value * mfd->panel_info.bl_max + MAX_BACKLIGHT_BRIGHTNESS)
  /(2 * MAX_BACKLIGHT_BRIGHTNESS);

 if (!bl_lvl && value)
  bl_lvl = 1;

 msm_fb_set_backlight(mfd, bl_lvl, 1);
}

static struct led_classdev backlight_led = {
 .name  = "lcd-backlight",
 .brightness = MAX_BACKLIGHT_BRIGHTNESS,
 .brightness_set = msm_fb_set_bl_brightness,
};

 

 

 if (!lcd_backlight_registered) {
  if (led_classdev_register(&pdev->dev, &backlight_led))
   printk(KERN_ERR "led_classdev_register failed/n");
  else
   lcd_backlight_registered = 1;
 }

就在目录/sys/class/leds创建子目录 lcd-backlight和属性文件brightness

当按键或者来的或者改变lcd亮度时，上层对属性文件/sys/class/leds/lcd-backlight/brightness写入背光的亮度数值就

调用led_brightness_store

调用simple_strtoul(buf, &after, 10);将输入的字符串转换为10进制的数字

执行led_set_brightness

执行led_cdev->brightness_set(led_cdev, value

调用msm_fb_set_bl_brightness ，因为  .brightness_set = msm_fb_set_bl_brightness,

 /* This maps android backlight level 0 to 255 into    driver backlight level 0 to bl_max with rounding */
 bl_lvl = (2 * value * mfd->panel_info.bl_max + MAX_BACKLIGHT_BRIGHTNESS)  /(2 * MAX_BACKLIGHT_BRIGHTNESS);
将输入的0--255转换为IC的0--bl_max

调用 msm_fb_set_backlight(mfd, bl_lvl, 1);

最终改变LCD的背光驱动电路的设置，调节LCD的背光的亮度

 

 

4.4 键盘背光灯

上层对属性文件/sys/class/leds/keyboard-backlight/brightness写入背光的亮度数值

 

(kernel/drivers/leds/Leds-msm-pmic.c

#define MAX_KEYPAD_BL_LEVEL 16

static void msm_keypad_bl_led_set(struct led_classdev *led_cdev,
 enum led_brightness value)
{
 int ret;

 ret = pmic_set_led_intensity(LED_KEYPAD, value / MAX_KEYPAD_BL_LEVEL);
 if (ret)
  dev_err(led_cdev->dev, "can't set keypad backlight/n");
}

static struct led_classdev msm_kp_bl_led = {
 .name   = "keyboard-backlight",
 .brightness_set  = msm_keypad_bl_led_set,
 .brightness  = LED_OFF,
};

static int msm_pmic_led_probe(struct platform_device *pdev)
{
 int rc;

 rc = led_classdev_register(&pdev->dev, &msm_kp_bl_led);
 if (rc) {
  dev_err(&pdev->dev, "unable to register led class driver/n");
  return rc;
 }
 msm_keypad_bl_led_set(&msm_kp_bl_led, LED_OFF);
 return rc;
}

static int __devexit msm_pmic_led_remove(struct platform_device *pdev)
{
 led_classdev_unregister(&msm_kp_bl_led);

 return 0;
}

#ifdef CONFIG_PM
static int msm_pmic_led_suspend(struct platform_device *dev,
  pm_message_t state)
{
 led_classdev_suspend(&msm_kp_bl_led);

 return 0;
}

static int msm_pmic_led_resume(struct platform_device *dev)
{
 led_classdev_resume(&msm_kp_bl_led);

 return 0;
}
#else
#define msm_pmic_led_suspend NULL
#define msm_pmic_led_resume NULL
#endif

static struct platform_driver msm_pmic_led_driver = {
 .probe  = msm_pmic_led_probe,
 .remove  = __devexit_p(msm_pmic_led_remove),
 .suspend = msm_pmic_led_suspend,
 .resume  = msm_pmic_led_resume,
 .driver  = {
  .name = "pmic-leds",
  .owner = THIS_MODULE,
 },
};

static int __init msm_pmic_led_init(void)
{
 return platform_driver_register(&msm_pmic_led_driver);
}
module_init(msm_pmic_led_init);

static void __exit msm_pmic_led_exit(void)
{
 platform_driver_unregister(&msm_pmic_led_driver);
}
module_exit(msm_pmic_led_exit);

MODULE_DESCRIPTION("MSM PMIC LEDs driver");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform:p

 

系统行动执行msm_pmic_led_init(void)
调用 platform_driver_register(&msm_pmic_led_driver);

调用msm_pmic_led_probe

调用 led_classdev_register(&pdev->dev, &msm_kp_bl_led);

就在目录/sys/class/leds创建子目录 keyboard-backlight和属性文件brightness

当按键时，上层对属性文件/sys/class/leds/keyboard-backlight/brightness写入背光的亮度数值就

调用led_brightness_store

调用simple_strtoul(buf, &after, 10);将输入的字符串转换为10进制的数字

执行led_set_brightness

执行led_cdev->brightness_set(led_cdev, value

调用msm_keypad_bl_led_set ，因为 .brightness_set  = msm_keypad_bl_led_set,

调用 ret = pmic_set_led_intensity(LED_KEYPAD, value / MAX_KEYPAD_BL_LEVEL);
最终改变LED驱动电路的设置，调节LED的亮度