Windlight is the snazzy name for the system used in-world in SL to tweak sky and water appearances. It’s great for taking photographs that have an extra ‘something.’ See the Wiki for a more detailed explanation of what it does.
I use Greenlife’s Emerald Viewer instead of the standard Linden Labs viewer. Among its many improvements, it includes considerably more preset sky settings to play with. I’ve been trying to find one that says “Christmas” to me, and ended up taking one called [Euphoria] Natural High and tweaking it a bit to create something I call Winter Wonderland. I thought, “I should share this,” and spent the next 10 minutes trying to find the file. I finally got smart and checked the Wiki:
Windows XP
* Skies – C:\Documents and Settings\USERNAME\Application Data\SecondLife\user_settings\windlight\skies
* Water – C:\Program Files\SecondLife\app_settings\windlight\waterWindows Vista
* Skies – C:\Users\USERNAME\AppData\Roaming\SecondLife\user_settings\windlight\skies
* Water – C:\Program Files\SecondLife\app_settings\windlight\water
Those directories are both where you can find settings that you create and save yourself, and where you put Windlight files created by others so you can use them in-world.
So, without further ado, here is my first Windlight file to share with you all:
[Az] Winter Wonderland 1

I just found





