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Unity 3 takes lighting and rendering to a new level.
We rewrote the rendering engine and integrated
the world's best lightmapper. 
Deferred Renderer
With Unity 3 we rewrote the entire rendering backend. Now, Unity Pro adds deferred lighting, using the modern light pre-pass technique.
Using deferred lighting, many lights are crazy fast, so now you can go wild and have light sources all over the place – even individual sparks from an explosion.
Realtime Shadows
Soft and hard realtime shadows can be cast from any light in the scene. A variety of strategies are used to make them really fast and even work on old computers.
Screen Space Ambient Occlusion
Unity Pro has SSAO as a standard image effect. Add this component to any camera and get a better looking game, it's really that simple. It fully integrates with the deferred lighting pipeline so the performance drop is nominal.
Sun Shafts & Lens Effects
Unity 3 Pro also adds sunshafts/godrays as a built-in effect. Simply add the component to a camera and get an immediate ambience boost.
Unity also simulates internal lens reflections and Hollywood-style flares, so you easily can achieve that cinematic look.
Lightmapping
When you want precise control over your game's ambience, lightmapping is really the only way to go. With Unity 3 we've integrated the world's best lightmapper, Beast. Now you can build scenes directly inside Unity and we'll make them beautiful.
Integration
Lighting is edited directly in the Unity Editor, so you get a perfect match between your baked backgrounds and realtime-lit objects. All emissive materials have an option to add bounce to the lightmap, so your neon signage will look just perfect.
Dual Lightmapping
Having perfectly lit environments is not everything, though. You also want your main characters to integrate nicely with your lightmaps. Unity supports dual lightmapping to do this: one lightmap is used for faraway stuff, while another contains only bounce light. Up close we fade in realtime direct lighting on top of the bounce lightmapped geometry. This means you don't need huge lightmaps for online games and moving the fade distance is a perfect way to adjust to the end-user's hardware capabilities in realtime.
UV Unwrap
You don't need to unwrap your models manually unless you want to – Unity will do it just fine. We also handle packing; in your scene you can prioritize objects with full visualization of where your lightmap space is spent.
Bake Away
Once it's time to bake, simply pull up the lightmap pane and configure your settings, then hit "bake". Unity will kick off a background job, letting you continue your work while it's running. For full control you can specify a Beast configuration and tell Unity to use that – this way you can truly unlock the full range of esoteric options that Beast offers.
