Create panel > Lights > Create light. > General Parameters rollout > Exclude button
The Exclude/Include dialog determines which objects are not illuminated by the selected light.
Although light exclusion does not occur in nature, this feature is useful when you need exact control over the lighting in your scene. Sometimes, for example, you'll want to add lights specifically to illuminate a single object but not its surroundings, or you'll want a light to cast shadows from one object but not from another.
Procedures
To exclude objects from a light:
In the General Parameters rollout, click Exclude.
The Exclude/Include dialog is displayed.
Make sure Exclude is on.
Choose to exclude objects from Illumination, Shadow Casting, or Both.
In the list of object names on the left, highlight the objects you want to exclude.
Click the arrow pointing to the right to move the selected object names into the right-hand list.
Objects in the right-hand list will be excluded. To remove an object from this list, highlight its name and click the arrow pointing to the left. To remove all objects from this list, click Clear.
Click OK.
Now when you shade or render the scene, the light will have no effect on the objects you chose.
The object still appears lit in shaded viewports. Exclusion takes effect only when you apply vertex colors.
To include objects that were excluded:
Click Exclude.
The Exclude/Include dialog is displayed.
Select the names of objects in the right-hand list, and then click the arrow pointing to the left.
Click OK.
To include all excluded objects at once:
Click Exclude or Include.
The Exclude/Include dialog is displayed.
Click Clear.
Click OK.
Interface
The Exclude/Include dialog contains the following controls:
Exclude/Include: Determines whether the light will exclude or include the objects named in the list on the right.
Illumination: Excludes or includes illumination of the object's surface.
Shadow Casting: Excludes or includes creation of the object's shadow.
Both: Excludes or includes both of the above.
Scene Objects: Select objects from the Scene Objects list on the left, then use the arrow buttons to add them to the exclusion list on the right.
The Exclude/Include dialog treats a group as an object. You can exclude or include all objects in a group by selecting the group's name in the Scene Objects list. If a group is nested within another group, it isn't visible in the Scene Objects list. To exclude a nested group or individual objects within the group, you have to ungroup them before you use this dialog.
Search field: The edit box above the Scene Objects list searches for objects by name. You can enter names that use wildcards.
Display Subtree: Indents the Scene Objects list according to the object hierarchy.
Case Sensitive: Uses case sensitivity when searching object names.
Selection Sets: Displays a list of named selection sets. Choosing a selection set from this list selects those objects in the Scene Objects list.
Clear: Clears all entries from the Exclude/Include list on the right.