diff --git a/out.jpg b/out.jpg
index 5660126..1cf4f11 100644
Binary files a/out.jpg and b/out.jpg differ
diff --git a/tinyraytracer.cpp b/tinyraytracer.cpp
index 385df3a..bf5a582 100644
--- a/tinyraytracer.cpp
+++ b/tinyraytracer.cpp
@@ -5,6 +5,12 @@
 #include <vector>
 #include "geometry.h"
 
+struct Light {
+    Light(const Vec3f &p, const float &i) : position(p), intensity(i) {}
+    Vec3f position;
+    float intensity;
+};
+
 struct Material {
     Material(const Vec3f &color) : diffuse_color(color) {}
     Material() : diffuse_color() {}
@@ -46,7 +52,7 @@ bool scene_intersect(const Vec3f &orig, const Vec3f &dir, const std::vector<Sphe
     return spheres_dist<1000;
 }
 
-Vec3f cast_ray(const Vec3f &orig, const Vec3f &dir, const std::vector<Sphere> &spheres) {
+Vec3f cast_ray(const Vec3f &orig, const Vec3f &dir, const std::vector<Sphere> &spheres, const std::vector<Light> &lights) {
     Vec3f point, N;
     Material material;
 
@@ -54,10 +60,15 @@ Vec3f cast_ray(const Vec3f &orig, const Vec3f &dir, const std::vector<Sphere> &s
         return Vec3f(0.2, 0.7, 0.8); // background color
     }
 
-    return material.diffuse_color;
+    float diffuse_light_intensity = 0;
+    for (size_t i=0; i<lights.size(); i++) {
+        Vec3f light_dir      = (lights[i].position - point).normalize();
+        diffuse_light_intensity  += lights[i].intensity * std::max(0.f, light_dir*N);
+    }
+    return material.diffuse_color * diffuse_light_intensity;
 }
 
-void render(const std::vector<Sphere> &spheres) {
+void render(const std::vector<Sphere> &spheres, const std::vector<Light> &lights) {
     const int width    = 1024;
     const int height   = 768;
     const int fov      = M_PI/2.;
@@ -69,7 +80,7 @@ void render(const std::vector<Sphere> &spheres) {
             float x =  (2*(i + 0.5)/(float)width  - 1)*tan(fov/2.)*width/(float)height;
             float y = -(2*(j + 0.5)/(float)height - 1)*tan(fov/2.);
             Vec3f dir = Vec3f(x, y, -1).normalize();
-            framebuffer[i+j*width] = cast_ray(Vec3f(0,0,0), dir, spheres);
+            framebuffer[i+j*width] = cast_ray(Vec3f(0,0,0), dir, spheres, lights);
         }
     }
 
@@ -94,7 +105,10 @@ int main() {
     spheres.push_back(Sphere(Vec3f( 1.5, -0.5, -18), 3, red_rubber));
     spheres.push_back(Sphere(Vec3f( 7,    5,   -18), 4,      ivory));
 
-    render(spheres);
+    std::vector<Light>  lights;
+    lights.push_back(Light(Vec3f(-20, 20,  20), 1.5));
+
+    render(spheres, lights);
 
     return 0;
 }