diff --git a/sim/state/light.ts b/sim/state/light.ts
index cbf98c2b..a2616fd3 100644
--- a/sim/state/light.ts
+++ b/sim/state/light.ts
@@ -14,7 +14,9 @@ namespace pxsim.output {
     export function setLights(pattern: number) {
         const brickState = ev3board().getBrickNode();
         const lightState = brickState.lightState;
-        lightState.lightPattern = pattern;
-        brickState.setChangedState();
+        if (lightState.lightPattern != pattern) {
+            lightState.lightPattern = pattern;
+            brickState.setChangedState();
+        }
     }
 }
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