Before you use sun/sky effect, you should setup sun correctly, because of this first we describe a method that you can use to setup sun.

• We start with a new scene in blender
• Then reset lamp rotation to zero, to do this select lamp and then press [N] key to see "Transform Properties" window, then set Rot X, Rot Y and Rot Z to 0.00.(i.e. noon)
  
• After that, if you want you can also change its rotation to other day times, you can change Rot X, or Rot Z, change Rot X in range[-90,90], you can change view to Side view [NUM3] and change Rot X in this range and see how it changes. Also change Rot Z in range[0,360] and to see its changes in this range go to Top view [NUM7]. for this doc we use Rot X:-70.0 and Rot Z:35.0.

To see sky, and even sun you should rotate camera such that it looks above horizon.

To enable sky effect for a lamp you should do these steps:

1. Create a Sun Lamp, and go to the Shading/Lamp panels [F5]
2. In the Sky/Atmosphere panel, enable either the sky or Atmosphere buttons

Note that by default world horizon color will add to the sky color generated by the sun lamp. You can change the blending mode to Mix in order to replace the default background colour, or any other blend mode, too.

• Hor.Brght or Horizontal Brightness, controls brightness of horizon colors, Its value should be in range [0,10], values near zero means no horizontal brighness, and large values for this paramtere increase horizon brightness. See below table for some values.
• Hor.Spread or Horizontal Spread, controls spread of light at horizon, its value should be in range [0,10], low values in the range result in less spread of light at horizon, and high values in the range result all horizon light spread in sky.
• Sun Brght or Sun Brightness, controls sun brightness, its value should be in range[0,10], with low values the sky has no sun and with high values sky only have sun.
• Sun Size controls size of sun, its values should be in range[0,10], but note that low values result in large sun size, and high values result in small sun size. also this parameter controls the light emited from sun, high values result in more light emit from sun.
• Back Light or Back Scatter Light, result on sun's color, high values result on more light around the sun.its values range is [-1,1]. negative values result on no more light around sun. In bellow render results we change default value for Sun Brght to 2.5.

Is a general parameter that affects sun view, sky and atmosphere, it's an atmosphere parameters that low values describe clear sky, and high values shows more foggy sky.

In this section we introduce atmosphere parameters, We change default values for sun parameters and use 0.2 for Hor. Brgh, and 2.0 for Sun Brght.

• Sun Intensity Sets sun intensity. its values are in range [0,10]. High values result more blue light in far objects.
• Inscattering factor can be use to decrease the effect of light inscattered into atmosphere between camera and objects in scene. this value should be 1.0 but its change may result some nice not realistic images.
• Extinction factor can be use to decrese the effect of extiction light from objects in the scene, like Inscattering factor, this parameter should be 1.0 but you can change it, low values result in less light extinction.its value is in range[0,1].
• Distance factor used to convert blender unit into an understandable unit for atmosphere effect, it starts from 0 and high vallues result in more yellow light into scene.

Note:

Atmosphere shading currently works incorrectly in reflections and refractions and is only supported for solid shaded surfaces. This will be addressed in a later release.