Lightning is an extension that adds calendar functionality to Thunderbird. You can create your own calendars, subscribe to calendars on the web and manage your own schedule, all within Thunderbird. Lightning also includes a Task manager that allows you to manage an integrated calendar and to-do list.
Starting with Thunderbird 38, Lightning is bundled with Thunderbird. This means you don't need to install it separately, but simply confirm to use it once you create a new profile or upgrade from a previous version of Thunderbird.
After the Lightning add-on is installed, the interface displays three panels: the calendar overview (on the left), the selected date / duration (in the middle) and the task list (on the right):
The Lightning add-on adds a new menu option to Thunderbird:
You can use this menu to add events and tasks, change the display, and perform various other functions. There also keyboard shortcuts for frequently used actions.
When the Task window is displayed, you can view and manage tasks, including setting the priority, completion status, category, etc. Tasks are associated with calendars; you must selected the desired calendar in the left panel to display the associated tasks.
By right-clicking a calendar entry you can create a corresponding task. Similarly, by right-clicking a task you can create an event.
The following articles describe how to install, configure and use Lightning.