page.title=Implementing Night Light
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    <h2>In this document</h2>
    <ol id="auto-toc">
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<p>
Research suggests that blue light from screens can have a negative impact on
sleep. Android 7.1.1 includes a feature called Night Light that reduces the
amount of blue light emitted by the device display to better match the natural
light of the user's time of day and location.
</p>
<p>
Night Light requires a
<a href="{@docRoot}devices/graphics/implement-hwc.html">Hardware
Composer HAL 2.0</a> (HWC 2) implementation that can apply the matrix passed to
<code>setColorTransform</code> to perform tinting without impacting power,
performance, and app compatibility.
</p>
<h2 id="implementation">Implementation</h2>
<p>
Device manufacturers can enable the default implementation of the feature by
using the following flags defined in:
<code><a href="https://android.googlesource.com/platform/frameworks/base/+/master/core/res/res/values/config.xml">
/android/frameworks/base/core/res/res/values/config.xml</a></code>

<pre>&lt;!-- Control whether Night display is available. This should only be enabled
      on devices with HWC 2 color transform  support. --&gt;
 &lt;bool name="config_nightDisplayAvailable">false&lt;/bool&gt;
 &lt;!-- Default mode to control how Night display is automatically activated.
      One of the following values (see NightDisplayController.java):
          0 - AUTO_MODE_DISABLED
          1 - AUTO_MODE_CUSTOM
          2 - AUTO_MODE_TWILIGHT
 --&gt;
 &lt;integer name="config_defaultNightDisplayAutoMode">0&lt;/integer&gt;
 &lt;!-- Default time when Night display is automatically activated.
      Represented as milliseconds from midnight (e.g. 79200000 == 10pm). --&gt;
 &lt;integer name="config_defaultNightDisplayCustomStartTime">79200000&lt;/integer&gt;
 &lt;!-- Default time when Night display is automatically deactivated.
      Represented as milliseconds from midnight (e.g. 21600000 == 6am). --&gt;
 &lt;integer name="config_defaultNightDisplayCustomEndTime">21600000&lt;/integer&gt;
</pre>
<p>
The code is divided between framework, system services, SystemUI, and Settings:
</p>
<pre>platform/frameworks/base/core
├ java/android/provider/Settings.java
├ java/com/android/internal/app/NightDisplayController.java
└ res/res/values/config.xml

platform/frameworks/base/proto/src/metrics_constants.proto

platform/frameworks/base/services
├ core/java/com/android/server/display/DisplayManagerService.java
├ core/java/com/android/server/display/DisplayTransformManager.java
├ core/java/com/android/server/display/NightDisplayService.java
└ java/com/android/server/SystemServer.java

platform/frameworks/base/packages/SystemUI
├ res/drawable/ic_qs_night_display_off.xml
├ res/drawable/ic_qs_night_display_on.xml
├ res/values/strings.xml
└ src/com/android/systemui/qs/tiles/NightDisplayTile.java

platform/packages/apps/Settings
├ AndroidManifest.xml
├ res/drawable/ic_settings_night_display.xml
├ res/values/strings.xml
├ res/xml/display_settings.xml
├ res/xml/night_display_settings.xml
├ src/com/android/settings/Settings.java
├ src/com/android/settings/dashboard/conditional/NightDisplayCondition.java
├ src/com/android/settings/display/NightDisplayPreference.java
└ src/com/android/settings/display/NightDisplaySettings.java
</pre>

<h2 id="ui-features">UI features</h2>
<p>
Because Night Light is a user-facing feature, users need to be able to control
it. There is a full implementation of the settings in the Android Open Source
Project (AOSP)
<a href="https://android.googlesource.com/platform/packages/apps/Settings/">packages/apps/Settings</a>
project that device manufacturers can reference for their Settings
implementation.
</p>
<h3 id="settings">Settings</h3>
<p>
The settings for Night Light are in <em>Settings &gt; Display &gt; Night
Light</em>. From there, users can learn about Night Light, set its schedule,
and turn it on or off.
</p>
<ul>
  <li><strong>Turn On Automatically</strong>
    <ul>
     <li><strong>Never</strong>: Night Light will never turn on automatically and
         must be activated with the  manual <strong>On / Off</strong> toggle.</li>
     <li><strong>Custom schedule</strong>: Night Light turns on at a specified
         <strong>Start time </strong>[default: 10:30 p.m.] and off at a specified
         <strong>End time</strong> [default: 6:30 a.m.].</li>
     <li><strong>Sunset to sunrise</strong>: Night Light turns on at sunset and off
         at sunrise. The time for sunrise and sunset depends on the device location
         and the time of year.</li>
    </ul>
  </li>
  <li><strong>On / Off</strong>: Toggle that controls the current state of Night
  Light. This state respects existing  automatic rules. For example, if Night
  Light is toggled on at 5:30 p.m. (before the automatic rule would turn it on
  at 10:30 p.m.), Night Light will still turn off at 6:30 a.m. And if Night
  Light is toggled off at 5:30 a.m. (before it turns off at 6:30 a.m.), it will
  still turn on at 10:30 p.m.</li>
  <li><strong>Informational text</strong>: Teaches the user what Night Light does
  and why.</li>
</ul>
<h3 id="settings-conditional">Settings conditional</h3>
<p>
Visible at the top of Settings when Night Light is on.
</p>
<h3 id="quick-settings-tile">Quick Settings tile</h3>
<p>
The Quick Settings tile behaves identically to the <strong>On / Off</strong>
toggle in <em>Settings &gt; Display &gt; Night Light</em>.
</p>