diff --git a/disk.cpp b/disk.cpp
index 0a802d0..a03e145 100644
--- a/disk.cpp
+++ b/disk.cpp
@@ -1,12 +1,16 @@
-#include <glm/gtc/constants.hpp>
+#include <iostream>
+#include <cassert>
 
 #include "disk.hpp"
 #include "sampling.hpp"
 
+using glm::vec2;
 using glm::cos;
 using glm::sin;
 using glm::dot;
-using glm::pi;
+using glm::distance;
+using glm::cross;
+using glm::abs;
 
 bool Disk::intersect(Ray & r, float & t) const {
   float _t;
@@ -23,14 +27,15 @@ bool Disk::intersect(Ray & r, float & t) const {
 }
 
 vec3 Disk::sample_at_surface() const {
-  float theta = random01() * (2.0f * pi<float>());
-  float r = glm::sqrt(random01() * m_radius);
-  float x = r * cos(theta);
-  float y = r * sin(theta);
-  float z = 0.0f;
-  vec3 sample = vec3(x, y, z);
-  rotate_sample(sample, m_normal);
-  return sample;
+  float theta = random01() * pi2;
+  float r = random01() * m_radius;
+  vec3 nt, nb;
+  create_coords_system(m_normal, nt, nb);
+  float x = m_point.x + (r * cos(theta) * nt.x) + (r * sin(theta) * nb.x);
+  float y = m_point.y + (r * cos(theta) * nt.y) + (r * sin(theta) * nb.y);
+  float z = m_point.z + (r * cos(theta) * nt.z) + (r * sin(theta) * nb.z);
+
+  return vec3(x, y, z);
 }
 
 void Disk::calculate_inv_area() {
diff --git a/disk.hpp b/disk.hpp
index 9076670..7d032dc 100644
--- a/disk.hpp
+++ b/disk.hpp
@@ -3,25 +3,30 @@
 #define DISK_HPP
 
 #include <glm/glm.hpp>
+#include <glm/gtc/constants.hpp>
 
 #include "plane.hpp"
 
 using glm::vec3;
 using glm::normalize;
+using glm::pi;
 
 class Disk : public Plane {
 public:
   float m_radius;
   
   Disk(Material * mat = NULL): Plane(mat), m_radius(1.0f) {
+    pi2 = 2.0f * pi<float>();
     calculate_inv_area();
   }
 
   Disk(float x, float y, float z, float nx, float ny, float nz, float _r, Material * mat = NULL): Plane(x, y, z, nx, ny, nz, mat), m_radius(_r) {
+    pi2 = 2.0f * pi<float>();
     calculate_inv_area();
   }
 
   Disk(vec3 _p, vec3 _n, float _r, Material * mat = NULL): Plane(_p, _n, mat), m_radius(_r) {
+    pi2 = 2.0f * pi<float>();
     calculate_inv_area();
   }
 
@@ -32,6 +37,9 @@ public:
 
 protected:
   virtual void calculate_inv_area();
+
+private:
+  float pi2;
 };
 
 
diff --git a/disk_area_light.cpp b/disk_area_light.cpp
index c4378b2..388b483 100644
--- a/disk_area_light.cpp
+++ b/disk_area_light.cpp
@@ -5,29 +5,39 @@
 #include "ray.hpp"
 
 using glm::normalize;
-
-const float BIAS = 0.000001f;
+using glm::dot;
 
 vec3 DiskAreaLight::diffuse(vec3 normal, Ray & r, vec3 i_pos, Material & m) const {
-  float d, att;
+float d, att, ln_dot_d, d2, g;
   vec3 l_dir, ref;
 
   l_dir = normalize(direction(i_pos));
-  d = distance(i_pos);
-  att = 1.0f / (m_const_att + (m_lin_att * d) + (m_quad_att * (d * d)));
+  ln_dot_d = dot(-m_n_at_last_sample, l_dir);
+  if (ln_dot_d > 0.0f) {
+    d2 = glm::distance(m_last_sample, i_pos);
+    d2 *= d2;
+    g = ln_dot_d / d2;
+    d = distance(i_pos);
+    att = 1.0f / (m_const_att + (m_lin_att * d) + (m_quad_att * (d * d)));
+    return (att * m.m_brdf->diffuse(l_dir, normal, r, i_pos, m_diffuse) * g) / m_figure->pdf();
 
-  return (att * m.m_brdf->diffuse(l_dir, normal, r, i_pos, m_diffuse)) / m_figure->pdf();
+  } else
+    return vec3(0.0f);
 }
 
 vec3 DiskAreaLight::specular(vec3 normal, Ray & r, vec3 i_pos, Material & m) const {
-float d, att;
+  float d, att, ln_dot_d;
   vec3 l_dir, ref;
 
   l_dir = normalize(direction(i_pos));
-  d = distance(i_pos);
-  att = 1.0f / (m_const_att + (m_lin_att * d) + (m_quad_att * (d * d)));
+  ln_dot_d = dot(-m_n_at_last_sample, l_dir);
+  if (ln_dot_d > 0.0f) {
+    d = distance(i_pos);
+    att = 1.0f / (m_const_att + (m_lin_att * d) + (m_quad_att * (d * d)));
+    return (att * m.m_brdf->specular(l_dir, normal, r, i_pos, m_specular, m.m_shininess)) / m_figure->pdf();
 
-  return (att * m.m_brdf->specular(l_dir, normal, r, i_pos, m_specular, m.m_shininess)) / m_figure->pdf();
+  } else
+    return vec3(0.0f);
 }
 
 void DiskAreaLight::sample_at_surface(vec3 point) {
diff --git a/scenes/scene5.json b/scenes/scene5.json
index ca77857..e70c37f 100644
--- a/scenes/scene5.json
+++ b/scenes/scene5.json
@@ -13,8 +13,9 @@
 	}
     },
 
-    "sphere_area_light": {
+    "disk_area_light": {
 	"position": [0.0, 1.0, -2.0],
+	"normal": [0.0, -1.0, -2.0],
 	"radius": 0.15,
 	"material": {
 	    "emission": [1.0, 1.0, 1.0]
diff --git a/scenes/scene6.json b/scenes/scene6.json
index 40c72a2..b9b22d1 100644
--- a/scenes/scene6.json
+++ b/scenes/scene6.json
@@ -1,6 +1,7 @@
 {
-    "sphere_area_light": {
+    "disk_area_light": {
 	"position": [0.0, 0.75, -1.0],
+	"normal": [0.0, -1.0, 0.0],
 	"radius": 0.15,
 	"material": {
 	    "emission": [1.0, 1.0, 1.0]
diff --git a/sphere_area_light.cpp b/sphere_area_light.cpp
index 1552fbb..820517f 100644
--- a/sphere_area_light.cpp
+++ b/sphere_area_light.cpp
@@ -10,7 +10,7 @@ vec3 SphereAreaLight::diffuse(vec3 normal, Ray & r, vec3 i_pos, Material & m) co
   vec3 l_dir, ref;
 
   l_dir = normalize(direction(i_pos));
-  ln_dot_d = dot(-m_n_at_last_sample, l_dir);
+  ln_dot_d = dot(m_n_at_last_sample, l_dir);
   if (ln_dot_d > 0.0f) {
     d2 = glm::distance(m_last_sample, i_pos);
     d2 *= d2;
@@ -28,7 +28,7 @@ vec3 SphereAreaLight::specular(vec3 normal, Ray & r, vec3 i_pos, Material & m) c
   vec3 l_dir, ref;
 
   l_dir = normalize(direction(i_pos));
-  ln_dot_d = dot(-m_n_at_last_sample, l_dir);
+  ln_dot_d = dot(m_n_at_last_sample, l_dir);
   if (ln_dot_d > 0.0f) {
     d = distance(i_pos);
     att = 1.0f / (m_const_att + (m_lin_att * d) + (m_quad_att * (d * d)));