The Light > Lights Properties sub-palette controls if shadows and sub-surface scattering will be used with the selected light and the illumination falloff.
The Shadow On/Off button enables or disables shadow casting for this light in best render or BPR. Shadows can be defined using the modifiers below for Best Render or when using the BPR render the shadows will be modified in the Render>BPR Shadow menu.
Shadows are only seen in Best Render mode or in BPR when the Shadow option is enabled in the Render > Render Properties menu. Real-time shadows are enabled the same way and by adjustments in the Render > Preview Shadows menu.
The SSS button will enable SSS render capability when it is also enabled in the BPR settings found in the Render Palette. Materials will play a role in creating a realistic SSS render. The Shader Mixer on any Material will control the SSS transitions.
The Intensity Curve defines the illumination falloff of this light from its center to the edge of its influence.
The left side of the curve defines the light intensity where its influence is weakest; the right side defines the light intensity where surfaces are closest to the light source.