diff --git a/.gitignore b/.gitignore
index c65ce39..bf7cd72 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
 build/
 *.ppm
 *.zip
+.vscode/
+.cache/
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 801846f..dfefc30 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,8 +21,8 @@ add_compile_options(-DSTUDENT_SOLUTION)
 
 # When testing large scenes the debug mode will be very slow
 # so switch to release
-set(CMAKE_BUILD_TYPE Debug)
-#set(CMAKE_BUILD_TYPE Release)
+#set(CMAKE_BUILD_TYPE Debug)
+set(CMAKE_BUILD_TYPE Release)
 
 set(CMAKE_CXX_STANDARD 14)
 
diff --git a/src/Geometry.cc b/src/Geometry.cc
index 9a98549..0a29ab8 100644
--- a/src/Geometry.cc
+++ b/src/Geometry.cc
@@ -1,18 +1,42 @@
 #include "Geometry.h"
 
 #include <Eigen/Dense>
+#include <cmath>
+
+Vector3f Geometry::diffuse() const { return cd; }
+Vector3f Geometry::specular() const { return cs; }
+Vector3f Geometry::ambient() const { return ca; }
+float Geometry::coefDiffuse() const { return kd; }
+float Geometry::coefSpecular() const { return ks; }
+float Geometry::coefAmbient() const { return ka; }
+float Geometry::getPhong() const { return phong; }
 
 void Geometry::setTransform(const Matrix4f &transform) {
   this->transform = transform;
 }
 
-bool Sphere::intersect(const Ray &r) const {
+Optional<float> Sphere::intersect(const Ray &r) const {
   Vector3f originCenter = r.getOrigin() - center;
   float a = r.getDirection().dot(r.getDirection());
   float b = 2.0f * originCenter.dot(r.getDirection());
   float c = originCenter.dot(originCenter) - radius * radius;
 
-  return b * b - 4 * a * c >= 0;
+  float delta = b * b - 4 * a * c;
+  if (delta >= 0) {
+    float t1 = (-b + sqrt(delta)) / 2.0f / a;
+    float t2 = (-b - sqrt(delta)) / 2.0f / a;
+    float mint = std::min(t1, t2);
+    float maxt = std::max(t1, t2);
+    return maxt <= 0
+               ? Optional<float>::nullopt
+               : (mint < 0 ? Optional<float>(maxt) : Optional<float>(mint));
+  }
+
+  return Optional<float>::nullopt;
+}
+
+Vector3f Sphere::getNormal(const Vector3f &p) const {
+  return (p - center).normalized();
 }
 
 bool isInRectangle(const Vector3f &p, const Vector3f &a, const Vector3f &b,
@@ -26,18 +50,19 @@ bool isInRectangle(const Vector3f &p, const Vector3f &a, const Vector3f &b,
          (s1 <= 0 && s2 <= 0 && s3 <= 0 && s4 <= 0);
 }
 
-bool Rectangle::intersect(const Ray &r) const {
-  Vector3f normal = (p2 - p1).cross(p3 - p1).normalized();
-
+Optional<float> Rectangle::intersect(const Ray &r) const {
   float denom = normal.dot(r.getDirection());
   if (abs(denom) < 1e-6f)
-    return false;
+    return Optional<float>::nullopt;
 
   float t = -normal.dot(r.getOrigin() - p1) / denom;
   if (t <= 0)
-    return false;
+    return Optional<float>::nullopt;
 
   Vector3f p = r.getOrigin() + t * r.getDirection();
 
-  return isInRectangle(p, p1, p2, p3, p4, normal);
+  return isInRectangle(p, p1, p2, p3, p4, normal) ? Optional<float>(t)
+                                                  : Optional<float>::nullopt;
 }
+
+Vector3f Rectangle::getNormal(const Vector3f &p) const { return normal; }
diff --git a/src/Geometry.h b/src/Geometry.h
index d92709f..b3d1eee 100644
--- a/src/Geometry.h
+++ b/src/Geometry.h
@@ -1,13 +1,16 @@
 #ifndef GEOMETRY_H_
 #define GEOMETRY_H_
 
+#include "Optional.h"
 #include "Ray.h"
 
 #include <Eigen/Core>
+#include <Eigen/Dense>
 
 using Eigen::Matrix;
 using Eigen::Matrix4f;
 using Eigen::Vector3f;
+using utils::Optional;
 
 // Abstract class for Geometries
 class Geometry {
@@ -15,7 +18,8 @@ public:
   enum class Type { SPHERE, RECTANGLE };
 
   virtual ~Geometry() = default;
-  virtual bool intersect(const Ray &) const = 0;
+  virtual Optional<float> intersect(const Ray &) const = 0;
+  virtual Vector3f getNormal(const Vector3f &) const = 0;
 
 protected:
   Geometry(Type type, float ka, float kd, float ks, const Vector3f &ca,
@@ -29,6 +33,13 @@ protected:
   Matrix4f transform = Matrix4f::Identity();
 
 public:
+  Vector3f diffuse() const;
+  Vector3f specular() const;
+  Vector3f ambient() const;
+  float coefDiffuse() const;
+  float coefSpecular() const;
+  float coefAmbient() const;
+  float getPhong() const;
   void setTransform(const Matrix4f &);
 };
 
@@ -39,7 +50,8 @@ public:
       : Geometry(Type::SPHERE, ka, kd, ks, ca, cd, cs, pc), radius(radius),
         center(center) {}
 
-  bool intersect(const Ray &) const override;
+  Optional<float> intersect(const Ray &) const override;
+  Vector3f getNormal(const Vector3f &) const override;
 
 private:
   float radius;
@@ -52,12 +64,14 @@ public:
             const Vector3f &cs, float pc, const Vector3f &p1,
             const Vector3f &p2, const Vector3f &p3, const Vector3f &p4)
       : Geometry(Type::RECTANGLE, ka, kd, ks, ca, cd, cs, pc), p1(p1), p2(p2),
-        p3(p3), p4(p4) {}
+        p3(p3), p4(p4), normal((p2 - p1).cross(p3 - p1).normalized()) {}
 
-  bool intersect(const Ray &) const override;
+  Optional<float> intersect(const Ray &) const override;
+  Vector3f getNormal(const Vector3f &) const override;
 
 private:
   Vector3f p1, p2, p3, p4;
+  Vector3f normal;
 };
 
 #endif // !GEOMETRY_H_
diff --git a/src/HitRecord.cc b/src/HitRecord.cc
new file mode 100644
index 0000000..6a07ee7
--- /dev/null
+++ b/src/HitRecord.cc
@@ -0,0 +1,19 @@
+#include "HitRecord.h"
+
+bool HitRecord::operator<(const HitRecord &other) const {
+  return this->t > other.t; // to get the nearest t
+}
+
+Geometry *HitRecord::geometry() const { return g; }
+
+Vector3f HitRecord::getPoint() const {
+  return r.getOrigin() + t * r.getDirection();
+}
+
+Vector3f HitRecord::viewDirection() const {
+  return -r.getDirection().normalized();
+}
+
+Vector3f HitRecord::normal() const { return n; }
+
+void HitRecord::calcNormal() { n = g->getNormal(getPoint()); }
diff --git a/src/HitRecord.h b/src/HitRecord.h
new file mode 100644
index 0000000..c7fad17
--- /dev/null
+++ b/src/HitRecord.h
@@ -0,0 +1,29 @@
+#ifndef HITRECORD_H_
+#define HITRECORD_H_
+
+#include "Geometry.h"
+#include "Ray.h"
+#include <Eigen/Core>
+
+using Eigen::Vector3f;
+
+class HitRecord {
+public:
+  HitRecord(float t, const Ray &r, Geometry *g) : t(t), r(r), g(g) {}
+  bool operator<(const HitRecord &) const;
+
+private:
+  float t;
+  Ray r;
+  Vector3f n;
+  Geometry *g;
+
+public:
+  Geometry *geometry() const;
+  Vector3f getPoint() const;
+  Vector3f viewDirection() const;
+  Vector3f normal() const;
+  void calcNormal();
+};
+
+#endif // !HITRECORD_H_
diff --git a/src/Light.cc b/src/Light.cc
index 07d7c27..2b0030a 100644
--- a/src/Light.cc
+++ b/src/Light.cc
@@ -1,4 +1,6 @@
 #include "Light.h"
+#include <algorithm>
+#include <cmath>
 
 void Light::setTransform(const Matrix4f &transform) {
   this->transform = transform;
@@ -8,6 +10,55 @@ void Light::setGridSize(unsigned int gridSize) { this->gridSize = gridSize; }
 
 void Light::setUseCenter(bool useCenter) { this->useCenter = useCenter; }
 
-void PointLight::illumination() const {}
+void Light::setIsUse(bool isUse) { this->use = isUse; }
 
-void AreaLight::illumination() const {}
+Vector3f Light::getDiffuse() const { return diffuse; }
+
+Vector3f Light::getSpecular() const { return specular; }
+
+bool Light::isUse() const { return use; }
+
+Vector3f PointLight::illumination(const HitRecord &hit,
+                                  const vector<Geometry *> &geometries) const {
+  Vector3f shadingPoint = hit.getPoint();
+  Vector3f rayDirection = (center - shadingPoint).normalized();
+  Geometry *geometry = hit.geometry();
+  Ray shadowRay(shadingPoint, rayDirection);
+
+  for (auto g : geometries)
+    if (g != geometry && g->intersect(shadowRay).hasValue())
+      return Vector3f::Zero();
+
+  Vector3f ambient_ = geometry->coefAmbient() * geometry->ambient();
+
+  Vector3f diffuse_ = geometry->coefDiffuse() * geometry->diffuse().array() *
+                      diffuse.array() *
+                      std::max(0.0f, hit.normal().dot(rayDirection));
+
+  Vector3f halfWay = (hit.viewDirection() + rayDirection).normalized();
+  Vector3f specular_ =
+      geometry->coefSpecular() * geometry->specular().array() *
+      specular.array() *
+      pow(std::max(0.0f, hit.normal().dot(halfWay)), geometry->getPhong());
+
+  return specular_ + ambient_ + diffuse_;
+}
+
+Vector3f AreaLight::illumination(const HitRecord &hit,
+                                 const vector<Geometry *> &geometries) const {
+  Vector3f u = p4 - p1;
+  Vector3f v = p2 - p1;
+
+  Vector3f color = Vector3f::Zero();
+
+  if (useCenter) {
+    color += PointLight(*this, p1 + (u + v) / 2).illumination(hit, geometries);
+  } else {
+    for (int y = 0; y < gridSize; ++y)
+      for (int x = 0; x < gridSize; ++x)
+        color += PointLight(*this, p1 + (u * x + v * y) / gridSize)
+                     .illumination(hit, geometries);
+  }
+
+  return color / gridSize / gridSize;
+}
diff --git a/src/Light.h b/src/Light.h
index c708467..60afbce 100644
--- a/src/Light.h
+++ b/src/Light.h
@@ -1,11 +1,14 @@
 #ifndef LIGHT_H_
 #define LIGHT_H_
 
+#include "HitRecord.h"
 #include <Eigen/Core>
+#include <vector>
 
 using Eigen::Matrix;
 using Eigen::Matrix4f;
 using Eigen::Vector3f;
+using std::vector;
 
 // Abstract base class for Lights
 class Light {
@@ -13,7 +16,8 @@ public:
   enum class Type { Point, Area };
 
   virtual ~Light() = default;
-  virtual void illumination() const = 0;
+  virtual Vector3f illumination(const HitRecord &,
+                                const vector<Geometry *> &) const = 0;
 
 protected:
   Light(Type type, const Vector3f &id, const Vector3f &is)
@@ -25,23 +29,16 @@ protected:
   Matrix4f transform = Matrix4f::Identity(); // optional member `transform`
   unsigned int gridSize = 0;                 // optional member `n`
   bool useCenter = false;                    // optional member `usecenter`
+  bool use = true;                           // this appears in a json file
 
 public:
-  // setters for optional members
   void setTransform(const Matrix4f &);
   void setGridSize(unsigned int);
   void setUseCenter(bool);
-};
-
-class PointLight : public Light {
-public:
-  PointLight(const Vector3f &id, const Vector3f &is, Vector3f &center)
-      : Light(Type::Point, id, is), center(center) {}
-
-  virtual void illumination() const override;
-
-private:
-  Vector3f center;
+  void setIsUse(bool);
+  Vector3f getDiffuse() const;
+  Vector3f getSpecular() const;
+  bool isUse() const;
 };
 
 class AreaLight : public Light {
@@ -50,10 +47,26 @@ public:
             const Vector3f &p2, const Vector3f &p3, const Vector3f &p4)
       : Light(Type::Area, id, is), p1(p1), p2(p2), p3(p3), p4(p4) {}
 
-  virtual void illumination() const override;
+  virtual Vector3f illumination(const HitRecord &,
+                                const vector<Geometry *> &) const override;
 
 private:
   Vector3f p1, p2, p3, p4;
 };
 
+class PointLight : public Light {
+public:
+  PointLight(const Vector3f &id, const Vector3f &is, const Vector3f &center)
+      : Light(Type::Point, id, is), center(center) {}
+
+  PointLight(const AreaLight &al, const Vector3f &center)
+      : PointLight(al.getDiffuse(), al.getSpecular(), center) {}
+
+  virtual Vector3f illumination(const HitRecord &,
+                                const vector<Geometry *> &) const override;
+
+private:
+  Vector3f center;
+};
+
 #endif // !LIGHT_H_
diff --git a/src/Optional.h b/src/Optional.h
new file mode 100644
index 0000000..3b3a7d4
--- /dev/null
+++ b/src/Optional.h
@@ -0,0 +1,25 @@
+#ifndef OPTIONAL_H_
+
+namespace utils {
+
+// I write this class because we are using C++14
+// so std::optional is not available
+template <typename T> class Optional {
+public:
+  Optional() : hasValue_(false) {}
+  Optional(T value) : value_(value), hasValue_(true) {}
+
+  bool hasValue() const { return hasValue_; }
+  T value() const { return value_; }
+
+  static const Optional nullopt;
+
+private:
+  T value_;
+  bool hasValue_;
+};
+
+template <typename T> const Optional<T> Optional<T>::nullopt = Optional<T>();
+} // namespace utils
+
+#endif // !OPTIONAL_H_
diff --git a/src/Output.cc b/src/Output.cc
new file mode 100644
index 0000000..840212b
--- /dev/null
+++ b/src/Output.cc
@@ -0,0 +1,22 @@
+#include "Output.h"
+
+#include <fstream>
+
+void Output::write() {
+  std::ofstream fout(path, std::ios_base::out | std::ios_base::binary);
+  fout << "P6\n" << width << ' ' << height << '\n' << "255" << std::endl;
+
+  for (unsigned int y = 0; y < height; ++y)
+    for (unsigned int x = 0; x < width; ++x)
+      fout << (char)(255.0f * red[y * width + x])
+           << (char)(255.0f * green[y * width + x])
+           << (char)(255.0f * blue[y * width + x]);
+  fout.close();
+}
+
+float Output::r(int index) const { return red.at(index); }
+float Output::g(int index) const { return green.at(index); }
+float Output::b(int index) const { return blue.at(index); }
+void Output::r(int index, float value) { red.at(index) = value; }
+void Output::g(int index, float value) { green.at(index) = value; }
+void Output::b(int index, float value) { blue.at(index) = value; }
diff --git a/src/Output.h b/src/Output.h
new file mode 100644
index 0000000..d7a065d
--- /dev/null
+++ b/src/Output.h
@@ -0,0 +1,38 @@
+#ifndef OUTPUT_H_
+#define OUTPUT_H_
+
+#include <Eigen/Core>
+#include <string>
+#include <vector>
+
+using Eigen::Vector3f;
+using std::string;
+using std::vector;
+
+class Output {
+public:
+  Output(const Vector3f &bgc, string path, int w, int h)
+      : red(vector<float>(w * h + 1, bgc.x())),
+        green(vector<float>(w * h + 1, bgc.y())),
+        blue(vector<float>(w * h + 1, bgc.z())), path(path), width(w),
+        height(h) {}
+
+  void write();
+
+private:
+  int width, height;
+  string path;
+  vector<float> red;
+  vector<float> green;
+  vector<float> blue;
+
+public:
+  void r(int, float);
+  float r(int) const;
+  void g(int, float);
+  float g(int) const;
+  void b(int, float);
+  float b(int) const;
+};
+
+#endif // !OUTPUT_H_
diff --git a/src/Parser.cc b/src/Parser.cc
index 4d15d76..126c6b3 100644
--- a/src/Parser.cc
+++ b/src/Parser.cc
@@ -109,6 +109,7 @@ Light *Parser::getLight(const nlohmann::json &j) {
 
   l->setGridSize(j.value("n", 0));
   l->setUseCenter(j.value("usecenter", false));
+  l->setIsUse(j.value("use", true));
 
   return l;
 }
diff --git a/src/RayTracer.cc b/src/RayTracer.cc
index e9c93a1..c79add8 100644
--- a/src/RayTracer.cc
+++ b/src/RayTracer.cc
@@ -1,10 +1,15 @@
 #include "RayTracer.h"
 #include "../external/simpleppm.h"
+#include "HitRecord.h"
+#include "Output.h"
 #include "Parser.h"
 #include "Ray.h"
 
 #include <Eigen/Core>
 #include <cmath>
+#include <queue>
+
+using std::priority_queue;
 
 void RayTracer::parse() {
   for (auto i = json["output"].begin(); i != json["output"].end(); ++i)
@@ -22,14 +27,27 @@ Ray getRay(int x, int y, const Vector3f &camPos, const Vector3f &pxUpperLeft,
   return Ray(camPos, pxUpperLeft + x * du + y * dv - camPos);
 }
 
+void RayTracer::calculateColor(const HitRecord &hit, Output *buffer, int i) {
+  buffer->r(i, 0);
+  buffer->g(i, 0);
+  buffer->b(i, 0);
+  for (auto light : lights)
+    if (light->isUse()) {
+      Vector3f contribution =
+          light->illumination(hit, geometries).cwiseMax(0.0f).cwiseMin(1.0f) /
+          lights.size();
+      buffer->r(i, buffer->r(i) + contribution.x());
+      buffer->g(i, buffer->g(i) + contribution.y());
+      buffer->b(i, buffer->b(i) + contribution.z());
+    }
+}
+
 void RayTracer::render(Scene *scene) {
   int width = scene->getWidth();
   int height = scene->getHeight();
-  float fov = scene->getFov();
   Vector3f cameraPos = scene->getCenter();
   Vector3f lookAt = scene->getLookAt();
-  Vector3f up = scene->getUpVector();
-  float vpHeight = 2 * tan(fov / 180 * M_PI / 2) * lookAt.norm();
+  float vpHeight = 2 * tan(scene->getFov() / 180 * M_PI / 2) * lookAt.norm();
   float vpWidth = vpHeight * width / height;
   Vector3f vpU = Vector3f(vpWidth, 0, 0);
   Vector3f vpV = Vector3f(0, -vpHeight, 0);
@@ -39,30 +57,32 @@ void RayTracer::render(Scene *scene) {
   Vector3f vpUpperLeft = cameraPos + lookAt - vpU / 2.0 - vpV / 2.0;
   Vector3f pxUpperLeft = vpUpperLeft + (du + dv) / 2.0;
 
-  Buffer buffer(width * height * 3);
+  Output *buffer =
+      new Output(scene->getBackgroundColor(), scene->getName(), width, height);
+
   for (int y = 0; y < height; ++y)
     for (int x = 0; x < width; ++x) {
       Ray ray = getRay(x, y, cameraPos, pxUpperLeft, du, dv);
+      priority_queue<HitRecord> records;
+      for (auto g : geometries) {
+        Optional<float> t = g->intersect(ray);
+        if (t.hasValue())
+          records.push(HitRecord(t.value(), ray, g));
+      }
 
-      for (auto geometry : geometries)
-        if (geometry->intersect(ray)) {
-          buffer[3 * y * width + 3 * x + 0] = 1;
-          buffer[3 * y * width + 3 * x + 1] = 1;
-          buffer[3 * y * width + 3 * x + 2] = 1;
-          break;
-        }
+      if (!records.empty()) {
+        HitRecord hit = records.top();
+        hit.calcNormal();
+        calculateColor(hit, buffer, y * width + x);
+      }
     }
 
-  Task *task = new Task(scene, buffer);
-  tasks.push_back(task);
+  outputs.push_back(buffer);
 }
 
-void RayTracer::output(Task *task) {
-  string path = task->first->getName();
-  int width = task->first->getWidth();
-  int height = task->first->getHeight();
-
-  save_ppm(path, task->second, width, height);
+void RayTracer::output() {
+  for (auto output : outputs)
+    output->write();
 }
 
 void RayTracer::run() {
@@ -71,6 +91,5 @@ void RayTracer::run() {
   for (auto scene : scenes)
     render(scene);
 
-  for (auto task : tasks)
-    output(task);
+  output();
 }
diff --git a/src/RayTracer.h b/src/RayTracer.h
index 95c917c..43a9075 100644
--- a/src/RayTracer.h
+++ b/src/RayTracer.h
@@ -4,14 +4,11 @@
 #include "../external/json.hpp"
 #include "Geometry.h"
 #include "Light.h"
+#include "Output.h"
 #include "Scene.h"
 
-#include <utility>
 #include <vector>
 
-using Buffer = std::vector<double>;
-using Task = std::pair<Scene *, Buffer>;
-
 class RayTracer {
 public:
   RayTracer(const nlohmann::json &j) : json(j) {}
@@ -22,12 +19,12 @@ private:
   std::vector<Scene *> scenes;
   std::vector<Light *> lights;
   std::vector<Geometry *> geometries;
-
-  std::vector<Task *> tasks;
+  std::vector<Output *> outputs;
 
   void parse();
+  void calculateColor(const HitRecord &, Output *, int);
   void render(Scene *);
-  void output(Task *);
+  void output();
 };
 
 #endif // !RAY_TRACER_H_
diff --git a/src/Scene.cc b/src/Scene.cc
index 8533ff3..9c48128 100644
--- a/src/Scene.cc
+++ b/src/Scene.cc
@@ -14,6 +14,8 @@ Vector3f Scene::getUpVector() const { return up; }
 
 Vector3f Scene::getLookAt() const { return lookAt; }
 
+Vector3f Scene::getBackgroundColor() const { return backgroundColor; }
+
 void Scene::setRaysPerPixel(const Eigen::VectorXi &raysPerPixel) {
   this->raysPerPixel = raysPerPixel;
 }
diff --git a/src/Scene.h b/src/Scene.h
index 24a697e..8ac10e0 100644
--- a/src/Scene.h
+++ b/src/Scene.h
@@ -39,6 +39,7 @@ public:
   Vector3f getCenter() const;
   Vector3f getUpVector() const;
   Vector3f getLookAt() const;
+  Vector3f getBackgroundColor() const;
   void setRaysPerPixel(const Eigen::VectorXi &);
   void setAntialiasing(bool);
   void setTwoSideRender(bool);