Since May 21st, when Linden Lab announced that they had aquired Windward Mark Interactive, a company that already had a specialization in realistic clouds rendering and other superb graphics technologies, with their software called Nimble.
It was said back then that the implementation would go at a rapid pace. A FirstLook viewer appeared not too long after and a lot of hurray's, comments and suggestions came in. After this little preview period, the newly aquired team at Linden Lab worked on developing and de-bugging, and it was said that a new FirstLook viewer with windlight would be available in August. Since than, many residents have been looking forward to this and yesterday it finally arrived.

What is Windlight exactly?
Windlight is a whole new way of rendering just about everything in Second Life, that is not a prim. Although it does affect prims as well. Windlight is mostly about having prettier skies, more realistic clouds and alltogether much better views. Including better reflections on the water and other things, and a whole bunch of new settings so you can customize your own views. You can even set how much overcast you want in your own personalized sky.

Will this increase lag?
Probably on the contrary. With the experience that LL already has so far, and with the added experience of the newly added crew of Windward Mark, they basically have re-written the whole thing. And that usually is a good thing, because you don't have to mind too much about the old software and tweaking it. And with this release, some other features are introduced as well, like a different way of rendering other avatars who are beyond chat range. From that range on, they will be rendered in a 2d way which will especially be decreasing lag in busy places. You will not really notice it when you look at the people, except maybe some jerky movements here and there.
Why a FirstLook viewer?
After the first FirstLook release including Windlight, they did a lot of bug fixing, working on suggestions from residents and testing. This has resulted in a new version. But before incorporating it into the standard viewer, they probably want to do more bug fixing wherever needed, and see how the public at large responds to it. It is expected that not too long after this FirstLook viewer, there will be a new release of the standard viewer with Windlight. This usually takes one or two months.

Is Windlight optional?
For now it is. You can choose to have Windlight by using the FirstLook viewer. But when it will be included in the standard release viewer, it will not be optional. The old strangely twisting clouds and obviously virtual skies will finally be gone forever.
How do I get Windlight?
You can have Windlight by downloading the FirstLook viewer by clicking here. This is basically the latest standard viewer (version 1.18.5), but with Windlight added. You can install this viewer next to your standard viewer, so you can switch between the both of them. At least as long as this FirstLook viewer is there.