You need to be a bit more clearer here.
iCal is the name of an Apple software (the calendar application in OS X).
iCalendar is RFC 2445 (a format designed to transmit calendar-based data, such as events, and intentionally does not describe what to do with that data).
CalDAV is RFC 4791 (a standard allowing a client to access scheduling information on a remote server).
So how exactly are you client calendar software (Lightning) setup ?
Are they using "iCalendar" (ics) or "CalDAV"?
The first one (iCalendar) should not be used... |