In recent years, the importance of interior lighting in automobiles has been evolving from transportation to the space of peoples lives. In particular, the button light of a car is a key element for the emotional quality and atmosphere of the car as well as doz- ens of functions. The emotional quality of the interior lighting is determined by uniformity of the button graphic light. We have developed a light diffusion button resin using refractive index difference between the base polymer resin and the light diffusion additives. In this re- sult, we have increased the lighting uniformity up to 84%, which is the highest result among the major car manufacturers.