diff --git a/lib/Slic3r/GUI/3DScene.pm b/lib/Slic3r/GUI/3DScene.pm
index 13460cfed2..75c19d89ef 100644
--- a/lib/Slic3r/GUI/3DScene.pm
+++ b/lib/Slic3r/GUI/3DScene.pm
@@ -1753,8 +1753,8 @@ sub _vertex_shader_Gouraud {
 // normalized values for (-0.6/1.31, 0.6/1.31, 1./1.31)
 const vec3 LIGHT_TOP_DIR = vec3(-0.4574957, 0.4574957, 0.7624929);
 #define LIGHT_TOP_DIFFUSE    (0.8 * INTENSITY_CORRECTION)
-#define LIGHT_TOP_SPECULAR   (0.25 * INTENSITY_CORRECTION)
-#define LIGHT_TOP_SHININESS  200.0
+#define LIGHT_TOP_SPECULAR   (0.125 * INTENSITY_CORRECTION)
+#define LIGHT_TOP_SHININESS  20.0
 
 // normalized values for (1./1.43, 0.2/1.43, 1./1.43)
 const vec3 LIGHT_FRONT_DIR = vec3(0.6985074, 0.1397015, 0.6985074);
@@ -1784,15 +1784,9 @@ varying vec3 delta_box_max;
 
 void main()
 {
-    vec3 eye = -normalize((gl_ModelViewMatrix * gl_Vertex).xyz);
-
     // First transform the normal into camera space and normalize the result.
     vec3 normal = normalize(gl_NormalMatrix * gl_Normal);
     
-    // Now normalize the light's direction. Note that according to the OpenGL specification, the light is stored in eye space. 
-    // Also since we're talking about a directional light, the position field is actually direction.
-    vec3 halfVector = normalize(LIGHT_TOP_DIR + eye);
-    
     // Compute the cos of the angle between the normal and lights direction. The light is directional so the direction is constant for every vertex.
     // Since these two are normalized the cosine is the dot product. We also need to clamp the result to the [0,1] range.
     float NdotL = max(dot(normal, LIGHT_TOP_DIR), 0.0);
@@ -1801,7 +1795,7 @@ void main()
     intensity.y = 0.0;
 
     if (NdotL > 0.0)
-        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(normal, halfVector), 0.0), LIGHT_TOP_SHININESS);
+        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(normal, reflect(-LIGHT_TOP_DIR, normal)), 0.0), LIGHT_TOP_SHININESS);
 
     // Perform the same lighting calculation for the 2nd light source (no specular applied).
     NdotL = max(dot(normal, LIGHT_FRONT_DIR), 0.0);
@@ -1926,8 +1920,8 @@ sub _vertex_shader_variable_layer_height {
 
 const vec3 LIGHT_TOP_DIR = vec3(-0.4574957, 0.4574957, 0.7624929);
 #define LIGHT_TOP_DIFFUSE    (0.8 * INTENSITY_CORRECTION)
-#define LIGHT_TOP_SPECULAR   (0.25 * INTENSITY_CORRECTION)
-#define LIGHT_TOP_SHININESS  200.0
+#define LIGHT_TOP_SPECULAR   (0.125 * INTENSITY_CORRECTION)
+#define LIGHT_TOP_SHININESS  20.0
 
 const vec3 LIGHT_FRONT_DIR = vec3(0.6985074, 0.1397015, 0.6985074);
 #define LIGHT_FRONT_DIFFUSE  (0.3 * INTENSITY_CORRECTION)
@@ -1943,15 +1937,9 @@ varying float object_z;
 
 void main()
 {
-    vec3 eye = -normalize((gl_ModelViewMatrix * gl_Vertex).xyz);
-
     // First transform the normal into camera space and normalize the result.
     vec3 normal = normalize(gl_NormalMatrix * gl_Normal);
     
-    // Now normalize the light's direction. Note that according to the OpenGL specification, the light is stored in eye space. 
-    // Also since we're talking about a directional light, the position field is actually direction.
-    vec3 halfVector = normalize(LIGHT_TOP_DIR + eye);
-    
     // Compute the cos of the angle between the normal and lights direction. The light is directional so the direction is constant for every vertex.
     // Since these two are normalized the cosine is the dot product. We also need to clamp the result to the [0,1] range.
     float NdotL = max(dot(normal, LIGHT_TOP_DIR), 0.0);
@@ -1960,7 +1948,7 @@ void main()
     intensity.y = 0.0;
 
     if (NdotL > 0.0)
-        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(normal, halfVector), 0.0), LIGHT_TOP_SHININESS);
+        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(normal, reflect(-LIGHT_TOP_DIR, normal)), 0.0), LIGHT_TOP_SHININESS);
 
     // Perform the same lighting calculation for the 2nd light source (no specular)
     NdotL = max(dot(normal, LIGHT_FRONT_DIR), 0.0);