diff --git a/MUNGA_L4/L4VIDEO.cpp b/MUNGA_L4/L4VIDEO.cpp
index 4bb91ce..8c07e6f 100644
--- a/MUNGA_L4/L4VIDEO.cpp
+++ b/MUNGA_L4/L4VIDEO.cpp
@@ -17,6 +17,10 @@
 #include "..\munga\nttmgr.h"
 #include "..\munga\app.h"
 #include "l4particles.h"
+#include "l4padrio.h"			// PadRIO::IsActive, for the per-frame lamp sweep
+#include "..\munga\gaugrend.h"
+#include "..\munga\lamp.h"
+#include "..\munga\mode.h"
 #include "DXUtils.h"
 
 using namespace std;
@@ -5983,11 +5987,84 @@ void
 //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // Execute Method, performs the rendering of one frame
 //
+//
+//===========================================================================
+// RPSweepCockpitLamps
+//
+// Push the cockpit lamp STATE once per frame, instead of once per gauge
+// cycle.
+//
+// The on-screen vRIO buttons light themselves from PadRIO::GetLampState,
+// and they redraw with their MFD strip. What FILLS that store is
+// LampManager::Update -> AssertNewLampValue -> SetLamp, and that rides
+// the gauge renderer's FOREGROUND turn - which comes round only once per
+// full gauge cycle. On a busy map the cycle takes the best part of a
+// second, so the lit buttons froze and any flash stalled while the 3D
+// view, a separate per-frame render, stayed perfectly smooth. BT411 saw
+// the same thing on its glass surround and fixed it the same way.
+//
+// It is cheap: a sweep over the lamps, no raster, and AssertNewLampValue
+// already drops anything that has not changed - so this pushes no extra
+// traffic, it only stops changes arriving late.
+//
+// Only when a PadRIO is active, i.e. cockpit-less play. With real serial
+// hardware selected the pod keeps its authentic bandwidth-paced cadence,
+// untouched. RP412LAMPSWEEP=0 restores the once-per-cycle behaviour.
+//===========================================================================
+//
+static void
+	RPSweepCockpitLamps()
+{
+	static int
+		enabled = -1;
+
+	if (enabled < 0)
+	{
+		const char
+			*setting = getenv("RP412LAMPSWEEP");
+
+		enabled = (setting != NULL && setting[0] == '0') ? 0 : 1;
+	}
+	if (!enabled || !PadRIO::IsActive() || application == NULL)
+	{
+		return;
+	}
+
+	//
+	// Only while a mission is actually running. This is called from the
+	// top of the frame, ahead of the state switch below, so it would
+	// otherwise fire while the mission is still being built and the
+	// gauges do not exist yet.
+	//
+	if (application->GetApplicationState() != Application::RunningMission)
+	{
+		return;
+	}
+
+	GaugeRenderer
+		*renderer = application->GetGaugeRenderer();
+	ModeManager
+		*modes = application->GetModeManager();
+
+	if (renderer != NULL && modes != NULL)
+	{
+		LampManager
+			*lamps = renderer->GetLampManager();
+
+		if (lamps != NULL)
+		{
+			lamps->Update(modes->GetModeMask());
+		}
+	}
+}
+
 void DPLRenderer::ExecuteImplementation(RendererComplexity, RendererOrigin::InterestingEntityIterator* all_iterator)
 {
 	Component *component;
 	HRESULT hr;
 
+	RPSweepCockpitLamps();		// keep the lit buttons tracking the sim (see above)
+
 	// timing variables
    __int64 ticks = HiResNowTicks();
 #ifdef LOGFRAMERATE
diff --git a/RP_L4/RPL4ENVIRON.cpp b/RP_L4/RPL4ENVIRON.cpp
index 724cea9..47a4e96 100644
--- a/RP_L4/RPL4ENVIRON.cpp
+++ b/RP_L4/RPL4ENVIRON.cpp
@@ -201,6 +201,14 @@ namespace
 "# has stopped refreshing from one whose picture simply is not changing.\n"
 "#RP412GAUGEDIAG=1\n"
 "\n"
+"# 0 = light the on-screen cockpit buttons on the same slow cadence the\n"
+"# arcade pod's serial hardware used. The lamp state is filled once per\n"
+"# gauge cycle, so under the load described above the lit buttons froze\n"
+"# and flashing ones stalled while the 3D view stayed perfectly smooth.\n"
+"# On by default: the buttons are refreshed every frame instead. Ignored\n"
+"# when real RIO hardware is selected - the pod keeps its own cadence.\n"
+"#RP412LAMPSWEEP=0\n"
+"\n"
 "# 1 = Steam networking (lobbies, FakeIP mesh). Needs the Steam client\n"
 "# running and steam_appid.txt beside the exe; without them the game\n"
 "# logs the reason and falls back to plain TCP. 0 = TCP only.\n"