diff --git a/README.md b/README.md
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+++ b/README.md
@@ -36,6 +36,7 @@ This repository contains notes and codes for **Computer Graphics.**
 1. [Unit 1 - Graphics Primitives and Scan Conversion Algorithms](https://git.kska.io/sppu-se-comp-codes/CG/src/branch/main/notes/Unit%201)
 2. [Unit 2 - Polygon, Windowing and Clipping](https://git.kska.io/sppu-se-comp-codes/CG/src/branch/main/notes/Unit%202)
 3. [Unit 3 - 2D, 3D Transformations and Projections](https://git.kska.io/sppu-se-comp-codes/CG/src/branch/main/notes/Unit%203)
+4. [Unit 4 - Light, Colour, Shading and Hidden Surfaces](https://git.kska.io/sppu-se-comp-codes/CG/src/branch/main/notes/Unit%204/CG%20UNIT%204%20%28PPT%29.pdf)
 5. [Unit 5 - Curves and Fractals](https://git.kska.io/sppu-se-comp-codes/CG/src/branch/main/notes/Unit%205)
 
 ### Question Papers