There are two types of Thea Lights: Point Lights and Area Lights.
The correct way to create a Point Light is by creating a Cinema 4D Light object and apply a Thea Light Tag to it. In Thea Light tag you can see all the light parameters supported by Thea. Once you enable Override Light Object, the tag will supersede over the Light Object. That means the object parameters will not be taken into consideration and the tag parameters will be used instead. Also, as long as the Override Light Object is enabled, the tag's parameters will be synchronized with the ones in the object and every change to them will also affect the corresponding ones in the light object. That way the viewport shows the correct representation of the tag for parameters such as color and type. The supported types for Thea Lights are Omni, Spot, Sun, IES, Projector and Area.
All these light types create point lights, except for "Area" of course. There two ways to create an Area Light. The first one is via a Light Object and a Thea Light Tag with Area set as type. Then, you can proceed by choosing the area shape and set the light parameters. The other way to do it is via a Cinema 4D polygon (or primitive) with an Emitter material on it (as we have mentioned in the Materials chapter).
Even though it appears to be two different workflows, transparently it is the same. In Thea Render, area lights can be created only with a Thea Model paired with an emitter material. So basically, if you use a Cinema 4D Light Object along with Thea Light Tag to create your Area lights, internally the plugin will generate a Thea Model and a Thea Material with the emitter component enabled. The model will have the exact same size as defined in Light Object.
Soft Shadow: user can select if the light will create soft shadow to the objects that illuminates or not.
Radius (cm): Define the radius of the emitter in centimeters.
Radius Multiplier: A user multiplier for radius in order to tweak automatic radius generation for sun.
Color: Defines the desired color of the emitter.
Power: Define the power of the emitter in relation to the selected units.
Units: Select the unit of measurement (lumens, lm/m2, cd/m2, Watts, W/m2, W/sr, W/sr/m2, W/nm, W/nm/m2, W/nm/sr and W/nm/sr/m2)
Efficacy (lm/W): Sets the efficacy of the emitter. Maximum efficacy is 683 ln/W which corresponds to lights with no energy loss.
Attenuation: The attenuation of the emitter. Available options: None, Inverse, Inverse Square)
Falloff: Sets the fall off angle of the emitter in degrees. Fall off defines the maximum angle, after which, lighting is not emitted at all.
Hotspot: Sets the hot spot angle of the emitter in degrees. Hot spot represents the angle in which the light beam has a constant power.
Manual Sun: When checked, it allows you to set a custom color and intensity for the Sun.
Sun Power: Define the intensity of the Sun when Manual Sun is active.
IES File: Select the IES file that will be used for the light distribution.
Multiplier: Specifies the intensity of the IES light.
Width: Sets the width of the Projector’s light rectangular area.
Height: Sets the height of the Projector’s light rectangular area.
Size X (cm): Sets the size of the area emitter on the X-Axis.
Size Y (cm): Sets the size of the area emitter on the Y-Axis.
Size Z (cm): Sets the size of the area emitter on the Z-Axis.
Seen by camera: Makes the area light invisible to the camera.
Seen by rays: Makes the light to be invisible in both reflection and refraction.
Cast Shadows: The emitter will not cast shadows into the scene.
Passive Emitter: The emitter will not cast light into the scene.
Custom Light Evaluation
Except for the emitter components in Thea materials, Custom Light Evaluation is also supported in light objects. The same rules apply here as well. Disabling a property, will cause all affected objects to ignore this specific light.
As we have said above, Thea Light Tag offers a visual representation of all Thea Light parameters that exist in the engine. Nevertheless, there are might be Cinema 4D lights that don't have a Thea Light Tag applied to them, probably in old unmaintained scenes. Cinema 4D untagged Lights will still be converted into Thea Lights, but some heuristic rules have to be applied for the conversion to be correct.
In this case, those Thea Light parameters that exist in C4D Light as well (e.g. color, type) will be transferred as they are, while those Thea Light Parameters that don't exist in the Light Object will be transferred with the default value.