diff --git a/beam.mac b/beam.mac
index 1bc30285a3a5610e946c2192e8d0495bda8c0f49..0f3d223c41e2135f43a8c2eeca0b92d212502341 100644
--- a/beam.mac
+++ b/beam.mac
@@ -24,11 +24,11 @@
 /gps/pos/halfx 1.0 mm
 /gps/pos/halfy 0.5 mm
 
-# the LED is positione @ the focus of hte parabolic reflector of the LED system
+# the LED is positioned @ the focus of hte parabolic reflector of the LED system
 /gps/pos/rot1 1 0 0
 /gps/pos/rot2 0 0 1
 #/gps/pos/centre 0 0 0 mm
-/gps/pos/centre 28.80 625.750 -4.5 mm
+/gps/pos/centre 28.50 623.50 -5.00 mm
 
 # the photons are emitted around the y-axis
 /gps/ang/rot1 1 0 0
diff --git a/models/LED-GMS-light-guide.stl b/models/LED-GMS-light-guide.stl
index 4a03b3374a73f1dd3e5792f4a53a298fb5321978..20692da666ee1176e93318ed54e9c93f2bd86959 100755
Binary files a/models/LED-GMS-light-guide.stl and b/models/LED-GMS-light-guide.stl differ
diff --git a/src/DetectorConstruction.cc b/src/DetectorConstruction.cc
index 775a74ad25f51e2d513380f8a5768bf96d7d3338..665d73edc02d2c376e3cc577b8e8617ad0bedfce 100755
--- a/src/DetectorConstruction.cc
+++ b/src/DetectorConstruction.cc
@@ -365,7 +365,7 @@ bool CHECK_OVERLAPS = true;
 
   m_physIntSD.push_back(
     new G4PVPlacement(new G4RotationMatrix(),
-                                              G4ThreeVector( 28.50*mm, 65.00*mm, -5.75*mm),
+                                              G4ThreeVector( 28.50*mm, 65.00*mm, -5.50*mm),
                                               m_logicIntSD[1],
                                               "IntSD2",
                                               m_logicWorld,