To set a parcel windlight: (must be land owner)
Note: This blog covers the new EEP environment settings which are available on most of the viewers. The instructions are covered on Firestorm viewer, but similar options should be available on other viewers as well. For help please reach out to the support staff.
Select below menu option from top
World -> Environment -> My Environments
On My Environments pop-up window, Navigate to the preferred windlight setting (default environments should be available under Library -> Environments folder)
Select the environment setting and Right-Click
Select "Apply to Parcel" from the Right-Click Menu.
You can also select "Apply to myself" if you want to test or apply the settings just for yourself, others on the parcel will continue to see the default parcel environment setting.
Anyone visiting the parcel should be able to see the new sky settings.
Useful information from SL Community Knowledge Base and SL wiki: