This paper introduces a luminance intensity interface driven by grasping forces, and its application as a musical instrument. In traditional musical instruments, the relationship between the action and the generated sound is determined by the physical structures of the instruments. Moreover, the freedom of the musical performances is limited by the structures. We developed a ball-shaped interface with handheld size. A photo diode is embedded in the translucent rubber ball to reacts to the grasping force of the performer. The grasping force is detected as the luminance intensity. The performer can use the ball interface only by grasping directly but also by holding to the environmental light or shading it by hands. The output of the interface is fed to the sound generator and the relationship between the performer's action and the generated sound is determined by the instrumental program to make the universal musical instrument.