Because the Light Suite is typically a collection of assets rather than a standalone software installer, follow these steps to integrate it into C4D R20:
Click the button at the bottom of the window.
If you are using R20 but cannot find a compatible version of the Light Suite, remember that Arnold (C4DtoA) has its own native tools:
Launch Cinema 4D. Navigate to the top menu bar, click on (or Extensions in newer C4D versions), and verify that the Light Suite menu appears. Free and Legal Alternatives for C4D Lighting
Solid Angle Arnold for Cinema 4D (C4DtoA) installed and activated.