The Arnold Light Manager window offers an overview of all light sources in the scene (e.g. Arnold lights, C4D lights, Arnold Sky, mesh lights) and allows you to easily modify their most important parameters or assign them to different light groups. The Light Manager can be opened from the Plugins > C4DtoA > Arnold Light menu or from the AOVs tab in the Render Settings.
Light groups are listed in the tree on the left. The default group contains the light sources which are not assigned to any light group. The attributes are displayed next to each light allowing you to modify them. Changing an attribute applies to all selected lights. You can customize which attribute to show in the table via the View > Show attributes... menu.
Toolbar
Add Light
To add a new light to the scene, click on the Add Light... button and select the light from the popup menu.
Add Light Group
To add a new light group to the scene, click on the Add Light Group... button and type the group name in the popup window.
Remove Unused Light Groups
Removes all light groups from the scene which have no lights assigned to them.
Actions
Assign Light to Light Group
Select one or multiple lights and drag & drop them to a light group. Alternatively you can right click and select Move to group > [group name] from the context menu.
To move the selected lights to a new group press Alt + G or right click and select Move to group > <new> from the context menu.
Edit name
To change the name of a light or light group, double click on the name.
Select Lights
To select a light in the Attribute Manager, Alt + click on the light or right click and select Select in Attribute Manager from the context menu.
To select all lights assigned to a group, Alt + click on the light group.
Delete
To delete a light or a light group from the scene, press the Delete button or right click and select Remove from the context menu.
When a light group is removed, all lights assigned to the group are moved under the default group.
Mute and Solo
Mute means to disable the given light in the Renderer, solo means to disable all other lights making the selected one(s) the only visible.
To mute a light or light group, click the 
button next to a light or light group. Muting a group means to mute all lights assigned to the group.
To solo a light or light group, click the 
button next to a light or light group. Soloing a group means to solo all lights assigned to the group.
To mute or solo an individual light (exclusive mute/solo), Ctrl + click on the or button.