diff --git a/core/java/android/service/dreams/DreamService.java b/core/java/android/service/dreams/DreamService.java
index 4060b24..eee4668 100644
--- a/core/java/android/service/dreams/DreamService.java
+++ b/core/java/android/service/dreams/DreamService.java
@@ -263,6 +263,7 @@
     private boolean mCanDoze;
     private boolean mDozing;
     private boolean mWindowless;
+    private boolean mPreviewMode;
     private int mDozeScreenState = Display.STATE_UNKNOWN;
     private int mDozeScreenBrightness = PowerManager.BRIGHTNESS_DEFAULT;
 
@@ -647,12 +648,13 @@
     }
 
     /**
-     * Marks this dream as keeping the screen bright while dreaming.
+     * Marks this dream as keeping the screen bright while dreaming. In preview mode, the screen
+     * is always allowed to dim and overrides the value specified here.
      *
      * @param screenBright True to keep the screen bright while dreaming.
      */
     public void setScreenBright(boolean screenBright) {
-        if (mScreenBright != screenBright) {
+        if (mScreenBright != screenBright && !mPreviewMode) {
             mScreenBright = screenBright;
             int flag = WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON;
             applyWindowFlags(mScreenBright ? flag : 0, flag);
@@ -661,7 +663,7 @@
 
     /**
      * Returns whether this dream keeps the screen bright while dreaming.
-     * Defaults to false, allowing the screen to dim if necessary.
+     * Defaults to true, preventing the screen from dimming.
      *
      * @see #setScreenBright(boolean)
      */
@@ -1280,6 +1282,11 @@
 
         mDreamToken = dreamToken;
         mCanDoze = canDoze;
+        mPreviewMode = isPreviewMode;
+        if (mPreviewMode) {
+            // Allow screen to dim when in preview mode.
+            mScreenBright = false;
+        }
         // This is not a security check to prevent malicious dreams but a guard rail to stop
         // third-party dreams from being windowless and not working well as a result.
         if (mWindowless && !mCanDoze && !isCallerSystemUi()) {