diff --git a/main/Scene.cc b/main/Scene.cc
index 10888be..cf9681a 100644
--- a/main/Scene.cc
+++ b/main/Scene.cc
@@ -18,6 +18,8 @@
 
 using namespace std;
 
+#define MAX_AMBIENT_OCCLUSION_DISTANCE 50.0
+
 Scene::Scene(const map<string, const char *> & options,
              const char * filename)
 {
@@ -25,7 +27,7 @@ Scene::Scene(const map<string, const char *> & options,
     m_height = 600;
     m_multisample_level = 1;
     m_vfov = 60.0;
-    m_ambient_light = Color(0.1, 0.1, 0.1);
+    m_ambient_light = Color(0.2, 0.2, 0.2);
     m_max_depth = 10;
     m_exposure = 1.0f;
     m_transforms.push(Transform());
@@ -213,7 +215,8 @@ Color Scene::computePhong(const refptr<Material> material,
                           const Vector & surfacePoint,
                           const Vector & surfaceNormal)
 {
-    Color result = m_ambient_light * material->getAmbientColor();
+    Color result = m_ambient_light * material->getAmbientColor()
+        * calculateAmbientOcclusion(Ray(surfacePoint, surfaceNormal).shift(1e-7));
 
     Vector viewDirection = -viewRay.getDirection();
     double shininess = material->getShininess();
@@ -289,7 +292,7 @@ Color Scene::calculateLightContribution(const Ray & toLight,
                                          const Vector & lightPosition)
 {
     Color contrib(1.0, 1.0, 1.0);
-    double dist_to_light = lightPosition - toLight.getOrigin();
+    double dist_to_light = (lightPosition - toLight.getOrigin()).mag();
     double dist_so_far = 0.0;
 
     Ray currentRay = toLight;
@@ -320,3 +323,44 @@ Color Scene::calculateLightContribution(const Ray & toLight,
 
     return contrib;
 }
+
+Color Scene::calculateAmbientOcclusion(const Ray & surfaceNormal)
+{
+    Color result(1, 1, 1);
+    const int nISteps = 6, nJSteps = 3;
+    int nRays = 0;
+    Vector perpX = surfaceNormal.getDirection().getPerpendicular().normalize();
+    Vector perpY = (surfaceNormal.getDirection() * perpX).normalize();
+    double istep = 2.0 * M_PI / nISteps;
+    double jstep = M_PI_2 / nJSteps;
+    for (int i = 0; i < nISteps; i++)
+    {
+        int lim = i > 0 ? nJSteps : 1;
+        for (int j = 0; j < lim; j++)
+        {
+            Vector direction = cos(i * istep) * sin(j * jstep) * perpX
+                + sin(i * istep) * sin(j * jstep) * perpY
+                + cos(j * jstep) * surfaceNormal.getDirection();
+            Ray thisRay(surfaceNormal.getOrigin(), direction);
+            double dist = 0.0;
+            Color contrib(1, 1, 1);
+            while (contrib.r > 0.2 && contrib.g > 0.2 && contrib.b > 0.2)
+            {
+                Shape::Intersection hit = getRayClosestHit(thisRay);
+                if (hit.shape.isNull())
+                    break;
+                double hitDist = (hit.position - thisRay.getOrigin()).mag();
+                dist += hitDist;
+                if (dist > MAX_AMBIENT_OCCLUSION_DISTANCE)
+                    break;
+                contrib *= hit.shape->getMaterial()->getTransparency()
+                    * hit.shape->getMaterial()->getDiffuseColor();
+                thisRay = thisRay.shift(hitDist + 1E-7);
+            }
+            result += contrib;
+            nRays++;
+        }
+    }
+    result /= nRays;
+    return result;
+}
diff --git a/main/Scene.h b/main/Scene.h
index 99781eb..f068523 100644
--- a/main/Scene.h
+++ b/main/Scene.h
@@ -50,6 +50,7 @@ class Scene
                            const Vector & surfaceNormal);
         Color calculateLightContribution(const Ray & toLight,
                                          const Vector & lightPosition);
+        Color calculateAmbientOcclusion(const Ray & surfaceNormal);
 
         /* In Scene-load.cc */
         void load(const char * filename);
diff --git a/util/Color.h b/util/Color.h
index 448aa4c..8524f07 100644
--- a/util/Color.h
+++ b/util/Color.h
@@ -38,6 +38,8 @@ class Color
 
 Color operator+(const Color & c1, const Color & c2);
 Color operator-(const Color & c1, const Color & c2);
+static inline Color operator*(double d, const Color & c) { return c * d; }
+static inline Color operator/(double d, const Color & c) { return c / d; }
 std::ostream & operator<<(std::ostream & out, const Color & color);
 
 #endif
diff --git a/util/Vector.h b/util/Vector.h
index 687c389..136ddbd 100644
--- a/util/Vector.h
+++ b/util/Vector.h
@@ -19,7 +19,6 @@ class Vector
         double dist_to(const Vector & other) const;
         Vector proj(const Vector & target) const;
         Vector reflect(const Vector & target) const;
-        operator double() const { return mag(); }
         Vector getPerpendicular() const;
 
     protected:
@@ -33,5 +32,7 @@ Vector operator+(const Vector & v1, const Vector & v2);
 Vector operator-(const Vector & v1, const Vector & v2);
 Vector operator*(const Vector & v1, double scale);
 Vector operator/(const Vector & v1, double scale);
+static inline Vector operator*(double d, const Vector & v) { return v * d; }
+static inline Vector operator/(double d, const Vector & v) { return v / d; }
 
 #endif