diff --git a/main.cpp b/main.cpp
index 08b3a8a..5f06e21 100644
--- a/main.cpp
+++ b/main.cpp
@@ -35,6 +35,7 @@ static vec3 ** image;
 static void scene_1(vector<Figure *> & vf, vector<Light *> & vl, mat4x4 & i_model_view);
 static void scene_2(vector<Figure *> & vf, vector<Light *> & vl, mat4x4 & i_model_view);
 static void scene_3(vector<Figure *> & vf, vector<Light *> & vl, mat4x4 & i_model_view);
+static void scene_4(vector<Figure *> & vf, vector<Light *> & vl, mat4x4 & i_model_view);
 
 int main(int argc, char ** argv) {
   FILE * out;
@@ -363,3 +364,17 @@ static void scene_3(vector<Figure *> & vf, vector<Light *> & vl, mat4x4 & i_mode
 
   i_model_view = inverse(lookAt(eye, center, up));
 }
+
+static void scene_4(vector<Figure *> & vf, vector<Light *> & vl, mat4x4 & i_model_view) {
+  Sphere * s;
+  Plane * p;
+
+  s = new Sphere(0.0f, 0.0f, -2.0f, 1.0f);
+  s->m_mat.m_diffuse = vec3(1.0f, 1.0f, 0.0f);
+  vf.push_back(static_cast<Figure *>(s));
+
+  p = new Plane(vec3(0.0f, -1.0f, 0.0f), vec3(0.0f, 1.0f, 0.0f));
+  p->m_mat.m_diffuse = vec3(1.0f);
+  p->m_mat.m_specular = vec3(0.0f);
+  vf.push_back(static_cast<Figure *>(p));
+}
diff --git a/path_tracer.cpp b/path_tracer.cpp
index 7374db8..4fb648e 100644
--- a/path_tracer.cpp
+++ b/path_tracer.cpp
@@ -14,7 +14,7 @@ static const float PDF = (1.0f / (2.0f * pi<float>()));
 vec3 PathTracer::trace_ray(Ray & r, vector<Figure *> & v_figures, vector<Light *> & v_lights, unsigned int rec_level) const {
   float t, _t;
   Figure * _f;
-  vec3 n, color, i_pos, ref, sample, dir_diff_color, dir_spec_color, ind_color;
+  vec3 n, color, i_pos, ref, sample, dir_diff_color, dir_spec_color, ind_color, amb_color;
   Ray mv_r, sr, rr;
   bool vis;
   float kr, r1, r2;
@@ -35,7 +35,7 @@ vec3 PathTracer::trace_ray(Ray & r, vector<Figure *> & v_figures, vector<Light *
     // Take the intersection point and the normal of the surface at that point.
     i_pos = r.m_origin + (t * r.m_direction);
     n = _f->normal_at_int(r, t);
-
+    
     // Check if the material is not reflective/refractive.
     if( !_f->m_mat.m_refract) {
       // Calculate the direct lighting.
@@ -53,8 +53,8 @@ vec3 PathTracer::trace_ray(Ray & r, vector<Figure *> & v_figures, vector<Light *
 	}
 
 	// Evaluate the shading model accounting for visibility.
-	dir_diff_color += (vis ? 1.0f : 0.0f) * v_lights[l]->diffuse(n, r, t, _f->m_mat);
-	dir_spec_color += (vis ? 1.0f : 0.0f) * v_lights[l]->specular(n, r, t, _f->m_mat);
+	dir_diff_color += vis ? v_lights[l]->diffuse(n, r, t, _f->m_mat) : vec3(0.0f);
+	dir_spec_color += vis ? v_lights[l]->specular(n, r, t, _f->m_mat) : vec3(0.0f);
       }
 
       // If enabled, calculate indirect lighting contribution.
@@ -67,14 +67,35 @@ vec3 PathTracer::trace_ray(Ray & r, vector<Figure *> & v_figures, vector<Light *
 	ind_color += r1 * trace_ray(rr, v_figures, v_lights, rec_level + 1) / PDF;
       }
 
-      color += ((dir_diff_color + ind_color) * (_f->m_mat.m_diffuse / pi<float>())) + dir_spec_color;
+      // Calculate environment light contribution
+      if (BCKG_COLOR.r > 0.0f || BCKG_COLOR.g > 0.0f || BCKG_COLOR.b > 0.0f) {
+	vis = true;
+
+	r1 = random01();
+	r2 = random01();
+	sample = sample_hemisphere(r1, r2);
+	rotate_sample(sample, n);
+	rr = Ray(normalize(sample), i_pos + (sample * BIAS));
+
+	// Cast a shadow ray to determine visibility.
+	for (size_t f = 0; f < v_figures.size(); f++) {
+	  if (v_figures[f]->intersect(rr, _t)) {
+	    vis = false;
+	    break;
+	  }
+	}
+
+	amb_color = vis ? BCKG_COLOR * max(dot(n, rr.m_direction), 0.0f) / PDF : vec3(0.0f);
+      }
+      
+      color += ((dir_diff_color + ind_color + amb_color) * (_f->m_mat.m_diffuse / pi<float>())) + dir_spec_color;
 
       // Determine the specular reflection color.
       if (_f->m_mat.m_rho > 0.0f && rec_level < MAX_RECURSION) {
 	rr = Ray(normalize(reflect(r.m_direction, n)), i_pos + n * BIAS);
 	color += _f->m_mat.m_rho * trace_ray(rr, v_figures, v_lights, rec_level + 1);
       } else if (_f->m_mat.m_rho > 0.0f && rec_level >= MAX_RECURSION)
-	return vec3(0.0f);
+	  return vec3(0.0f);
 
     } else {
       // If the material has transmission enabled, calculate the Fresnel term.
@@ -92,7 +113,7 @@ vec3 PathTracer::trace_ray(Ray & r, vector<Figure *> & v_figures, vector<Light *
 	rr = Ray(normalize(refract(r.m_direction, n, r.m_ref_index / _f->m_mat.m_ref_index)), i_pos - n * BIAS, _f->m_mat.m_ref_index);
 	color += (1.0f - kr) * trace_ray(rr, v_figures, v_lights, rec_level + 1);
       } else if (rec_level >= MAX_RECURSION)
-	return vec3(0.0f);
+	  return vec3(0.0f);
 
     }
 
@@ -100,5 +121,5 @@ vec3 PathTracer::trace_ray(Ray & r, vector<Figure *> & v_figures, vector<Light *
     return clamp(color, 0.0f, 1.0f);
 
   } else
-    return vec3(BCKG_COLOR);
+    return /*vec3(0.0f)*/ BCKG_COLOR;
 }
diff --git a/sphere.cpp b/sphere.cpp
index 2811490..396f3fa 100644
--- a/sphere.cpp
+++ b/sphere.cpp
@@ -1,7 +1,6 @@
 #include "sphere.hpp"
 
-using glm::normalize;
-using glm::sqrt;
+using namespace glm;
 
 bool Sphere::intersect(Ray & r, float & t) const {
   float t1, t2;
diff --git a/tracer.cpp b/tracer.cpp
index 7692c93..7a91bb5 100644
--- a/tracer.cpp
+++ b/tracer.cpp
@@ -6,7 +6,7 @@
 
 using namespace glm;
 
-const vec3 BCKG_COLOR = vec3(0.0f, 0.2f, 0.6f);
+const vec3 BCKG_COLOR = vec3(1.0f);
 
 float Tracer::random01() const {
   return static_cast<float>(rand()) / static_cast<float>(RAND_MAX);