Page status (reviewing guidelines)
Environment light provides light coming from all directions. Light is calculated with a raytraced method which is the same as that used by Ambient Occlusion. The difference is that Environment lighting takes into account the "ambient" parameter of the material shading settings, which indicates the amount of ambient ligth/color that material receives. Also, you can choose the environment color source (white, sky color, sky texture) and the light energy.
Try to use both settings simultaneously to achieve better global lighting.
It's good for mimicking the sky in outdoor lighting. Environment lighting can be fairly noisy at times.