diff --git a/src/GameEngine.c b/src/GameEngine.c
index ccb10ab..7357377 100644
--- a/src/GameEngine.c
+++ b/src/GameEngine.c
@@ -13,6 +13,7 @@ const uint8_t MinHalfStars = 1;
 const uint16_t PerfectScore = 300; // LevelCount * MaxHalfStars
 
 void GameEngine_LoadLevel(GameEngine *pGameEngine, const int8_t level, const bool setB);
+uint8_t GameEngine_CalculateHalfStars(const uint16_t par, const uint16_t moves);
 void GameEngine_ToggleSingleLight(GameEngine *pGameEngine, const int8_t x, const int8_t y);
 
 void GameEngine_NewGame(GameEngine *pGameEngine, const bool setB)
@@ -39,6 +40,7 @@ void GameEngine_LoadLevel(GameEngine *pGameEngine, const int8_t level, const boo
 {
     pGameEngine->Level = level;
     pGameEngine->SetB = setB;
+    pGameEngine->PreviousLights = pGameEngine->Lights;
     pGameEngine->Lights = Levels_GetLightsForLevel(pGameEngine->Level, setB);
     pGameEngine->Par = Levels_GetParForLevel(pGameEngine->Level);
     pGameEngine->Moves = 0;
@@ -66,7 +68,12 @@ bool GameEngine_IsGameOver(const GameEngine *pGameEngine)
 
 uint8_t GameEngine_GetHalfStars(const GameEngine *pGameEngine)
 {
-    uint8_t halfStarsLost = pGameEngine->Moves <= pGameEngine->Par ? 0 : max(0, (1 + pGameEngine->Moves - pGameEngine->Par) / 2);
+    return GameEngine_CalculateHalfStars(pGameEngine->Par, pGameEngine->Moves);
+}
+
+uint8_t GameEngine_CalculateHalfStars(const uint16_t par, const uint16_t moves)
+{
+    uint8_t halfStarsLost = moves <= par ? 0 : max(0, (1 + moves - par) / 2);
     return max(MinHalfStars, MaxHalfStars - halfStarsLost);
 }
 
@@ -75,6 +82,8 @@ void GameEngine_ToggleLights(GameEngine *pGameEngine, const int8_t x, const int8
     int8_t targetX = max(0, min(x, PuzzleSize - 1));
     int8_t targetY = max(0, min(y, PuzzleSize - 1));
     
+    pGameEngine->PreviousLights = pGameEngine->Lights;
+    
     GameEngine_ToggleSingleLight(pGameEngine, targetX, targetY);
     GameEngine_ToggleSingleLight(pGameEngine, targetX + 1, targetY);
     GameEngine_ToggleSingleLight(pGameEngine, targetX, targetY + 1);
@@ -91,3 +100,19 @@ void GameEngine_ToggleSingleLight(GameEngine *pGameEngine, const int8_t x, const
         bitToggle(pGameEngine->Lights, y * PuzzleSize + x);
     }
 }
+
+bool GameEngine_LightChanged(const GameEngine *pGameEngine, const int8_t x, const int8_t y)
+{
+    if (x >= 0 && x < PuzzleSize && y >= 0 && y < PuzzleSize)
+    {
+        return bitRead(pGameEngine->Lights, y * PuzzleSize + x) != bitRead(pGameEngine->PreviousLights, y * PuzzleSize + x);
+    }
+    
+    return false;
+}
+
+bool GameEngine_HalfStarsChanged(const GameEngine *pGameEngine)
+{
+    return pGameEngine->Moves == 0 ||
+        GameEngine_CalculateHalfStars(pGameEngine->Par, pGameEngine->Moves - 1) != GameEngine_GetHalfStars(pGameEngine);
+}
diff --git a/src/GameEngine.h b/src/GameEngine.h
index 124bfb2..2a2e3d4 100644
--- a/src/GameEngine.h
+++ b/src/GameEngine.h
@@ -20,6 +20,7 @@ typedef struct GameEngine
     int8_t   Level;
     bool     SetB;
     uint32_t Lights;
+    uint32_t PreviousLights;
     uint16_t Par;
     uint16_t Moves;
 } GameEngine;
@@ -40,4 +41,8 @@ uint8_t GameEngine_GetHalfStars(const GameEngine *pGameEngine);
 
 void GameEngine_ToggleLights(GameEngine *pGameEngine, const int8_t x, const int8_t y);
 
+bool GameEngine_LightChanged(const GameEngine *pGameEngine, const int8_t x, const int8_t y);
+
+bool GameEngine_HalfStarsChanged(const GameEngine *pGameEngine);
+
 #endif
diff --git a/src/GameWindow.c b/src/GameWindow.c
index d59714d..e891366 100644
--- a/src/GameWindow.c
+++ b/src/GameWindow.c
@@ -110,8 +110,9 @@ void GameWindow_SetScene(GameWindow *pGameWindow, const SceneId sceneId)
             GameEndScene_Init(pGameWindow);
             break;
     }
+    
     pGameWindow->CurrentSceneId = sceneId;
-    GameWindow_Draw(pGameWindow, true);
+    GameWindow_Draw(pGameWindow, true); // Always force a full refresh when changing scenes
 }
 
 void GameWindow_Show(const GameWindow *pGameWindow)
diff --git a/src/MacLO.pi.bin b/src/MacLO.pi.bin
index 5b06658..c2bc12a 100644
Binary files a/src/MacLO.pi.bin and b/src/MacLO.pi.bin differ
diff --git a/src/MacLO.pi.rsrc.bin b/src/MacLO.pi.rsrc.bin
index f1e7fef..5817b7c 100644
Binary files a/src/MacLO.pi.rsrc.bin and b/src/MacLO.pi.rsrc.bin differ
diff --git a/src/PlayScene.c b/src/PlayScene.c
index 69c42e4..c192029 100644
--- a/src/PlayScene.c
+++ b/src/PlayScene.c
@@ -98,17 +98,20 @@ void PlayScene_Draw(const GameWindow *pGameWindow, bool fullRefresh)
     {
         for (c = 0; c < PuzzleSize; c++)
         {
-            PlayScene_SetLightRect(pGameWindow, &lightRect, c, r);
-            
-            if (GameEngine_GetLight(&(pGameWindow->Engine), c, r))
+            if (fullRefresh || GameEngine_LightChanged(&(pGameWindow->Engine), c, r))
             {
-                // Draw ON light
-                DrawPicture(pGameWindow->Bitmaps.LightOnPict, &lightRect);
-            }
-            else
-            {
-                // Draw OFF light
-                DrawPicture(pGameWindow->Bitmaps.LightOffPict, &lightRect);
+                PlayScene_SetLightRect(pGameWindow, &lightRect, c, r);
+                
+                if (GameEngine_GetLight(&(pGameWindow->Engine), c, r))
+                {
+                    // Draw ON light
+                    DrawPicture(pGameWindow->Bitmaps.LightOnPict, &lightRect);
+                }
+                else
+                {
+                    // Draw OFF light
+                    DrawPicture(pGameWindow->Bitmaps.LightOffPict, &lightRect);
+                }
             }
         }
     }
@@ -116,29 +119,41 @@ void PlayScene_Draw(const GameWindow *pGameWindow, bool fullRefresh)
     // Draw HUD
     
     // Draw level
-    MoveTo(pGameWindow->PlayScene.LevelRect.left, pGameWindow->PlayScene.LevelRect.top);
-    if (pGameWindow->Engine.SetB)
+    if (fullRefresh)
     {
-        Bitmaps_DrawBChar(&(pGameWindow->Bitmaps), LevelTextScale);
+        MoveTo(pGameWindow->PlayScene.LevelRect.left, pGameWindow->PlayScene.LevelRect.top);
+        if (pGameWindow->Engine.SetB)
+        {
+            Bitmaps_DrawBChar(&(pGameWindow->Bitmaps), LevelTextScale);
+        }
+        else
+        {
+            Bitmaps_DrawAChar(&(pGameWindow->Bitmaps), LevelTextScale);
+        }
+        Bitmaps_DrawNumber(&(pGameWindow->Bitmaps), 1 + pGameWindow->Engine.Level, LevelTextScale);
     }
-    else
-    {
-        Bitmaps_DrawAChar(&(pGameWindow->Bitmaps), LevelTextScale);
-    }
-    Bitmaps_DrawNumber(&(pGameWindow->Bitmaps), 1 + pGameWindow->Engine.Level, LevelTextScale);
     
     // Draw half-stars
-    MoveTo(pGameWindow->PlayScene.HalfStarsRect.left, pGameWindow->PlayScene.HalfStarsRect.top);
-    Bitmaps_DrawHalfStars(&(pGameWindow->Bitmaps), GameEngine_GetHalfStars(&(pGameWindow->Engine)), MaxStars, HalfStarScale);
+    if (fullRefresh || GameEngine_HalfStarsChanged(&(pGameWindow->Engine)))
+    {
+        MoveTo(pGameWindow->PlayScene.HalfStarsRect.left, pGameWindow->PlayScene.HalfStarsRect.top);
+        Bitmaps_DrawHalfStars(&(pGameWindow->Bitmaps), GameEngine_GetHalfStars(&(pGameWindow->Engine)), MaxStars, HalfStarScale);
+    }
     
     // Draw score
-    MoveTo(pGameWindow->PlayScene.ScoreRect.left, pGameWindow->PlayScene.ScoreRect.top);
-    Bitmaps_DrawNumber(&(pGameWindow->Bitmaps), pGameWindow->Engine.Score, ScoreTextScale);
-    Bitmaps_DrawSlashChar(&(pGameWindow->Bitmaps), ScoreTextScale);
-    Bitmaps_DrawNumber(&(pGameWindow->Bitmaps), PerfectScore, ScoreTextScale);
+    if (fullRefresh)
+    {
+        MoveTo(pGameWindow->PlayScene.ScoreRect.left, pGameWindow->PlayScene.ScoreRect.top);
+        Bitmaps_DrawNumber(&(pGameWindow->Bitmaps), pGameWindow->Engine.Score, ScoreTextScale);
+        Bitmaps_DrawSlashChar(&(pGameWindow->Bitmaps), ScoreTextScale);
+        Bitmaps_DrawNumber(&(pGameWindow->Bitmaps), PerfectScore, ScoreTextScale);
+    }
     
     // Draw retry button
-    DrawPicture(pGameWindow->Bitmaps.RetryButtonPict, &(pGameWindow->PlayScene.RetryButtonRect));
+    if (fullRefresh)
+    {
+        DrawPicture(pGameWindow->Bitmaps.RetryButtonPict, &(pGameWindow->PlayScene.RetryButtonRect));
+    }
     
     // Draw sound button
     MoveTo(pGameWindow->PlayScene.SoundButtonRect.left, pGameWindow->PlayScene.SoundButtonRect.top);