Unity supports different Rendering Paths. You should choose which one you use depending on your game content and target platform / hardware. Different rendering paths have different features and performance characteristics that mostly affect Lights and Shadows.
If the graphics card can’t handle a selected rendering path, Unity will automatically use a lower fidelity one. So on a GPU that can’t handle Deferred Lighting, Forward Rendering will be used. If Forward Rendering is not supported, Vertex Lit will be used.
Deferred Lighting is the rendering path with the most lighting and shadow fidelity. It is best used if you have many realtime lights. It requires a certain level of hardware support, is for Unity Pro only.
For more details see the Deferred Lighting page.
Forward is a shader-based rendering path. It supports per-pixel lighting (including normal maps & light Cookies) and realtime shadows from one directional light. In the default settings, a small number of the brightest lights are rendered in per-pixel lighting mode. The rest of the lights are calculated at object vertices.
For more details see the Forward Rendering page.
Vertex Lit is the rendering path with the lowest lighting fidelity and no support for realtime shadows. It is best used on old machines or limited mobile platforms.
For more details see the Vertex Lit page.
|Deferred Lighting||Forward Rendering||Vertex Lit|
|Per-pixel lighting (normal maps, light cookies)||Yes||Yes||-|
|Realtime shadows||Yes||1 Directional Light||-|
|Depth&Normals Buffers||Yes||Additional render passes||-|
|Light Culling Masks||Limited||Yes||Yes|
|Lighting Fidelity||All per-pixel||Some per-pixel||All per-vertex|
|Cost of a per-pixel Light||Number of pixels it illuminates||Number of pixels * Number of objects it illuminates||-|
|PC (Windows/Mac)||Shader Model 3.0+||Shader Model 2.0+||Anything|
|Mobile (iOS/Android)||OpenGL ES 2.0||OpenGL ES 2.0||OpenGL ES 2.0 & 1.1|
|Consoles||360, PS3||360, PS3||-|