SketchUp doesn’t have native light sources. Thea for SketchUp uses components with special names to define the position and orientation of lights. Four light types are available:
You can also apply an Emitter material to a face to create an indirect source of illumination. The front side of the face will glow.
To create a light, open the Thea Tool window and select the ‘Light’ tab. Click on one of the buttons at the bottom of the tab to create a point, spot, IES, or projector light. Right-click to place the light source, and right-click again to place its target. For point lights, only the distance from the source to the target is used to calculate the power needed to reach the target. It is important that the distance between the light source and any adjacent geometry is greater than the radius of the light; otherwise, the final rendering may contain undesired “noise.” Once created, the light's name and properties are displayed in the Light tab.
If a light looks faint in the rendering, check the exposure settings (ISO, Shutter speed, and f-number). For interior scenes, respective values of 800, 30, and 2.4 are usually sufficient.
Emittance properties are described in detail here: Editing Lights
Enabled: Turns the light On/Off.
Shadow (Presto): Turns shadowcasting On/Off.
Soft Shadow - radius (m): Makes the light cast soft shadows by changing the radius (in meters).
Container: If the light is placed inside a container made of a material with the properties of a medium, or if it is submerged in water, ‘Container’ lets you select a material for the container. It can be also used to show a volumetric projection of light.
Evaluation: Instructs the light whether it should affect the listed material properties. Example: If the Diffuse is unchecked, then the light will not affect the diffuse color of the object.