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The 3Delight Sky is a utility node that can be used for image based lighting of daylight conditions. It is very well suited as a fast lighting rig. 3Delight can extract sharp shadows using this shader so that no directional light is needed to cast shadows from the sun.

This shader is based on the Hosek-Wilkie sky model. It is an analytical model of the daytime sky that includes the latest improvement in this field of research. This model is able to properly picture sunsets and lighting in high turbidity environments - such as lighting during a moist day.

 


The Parameters

 

Parameters Description 
Intensity

This drives the overall intensity of the sky. It is a direct multiplier of the sky radiance function.

Intensity 1.0

Intensity 1.5

Intensity 2.0

Turbidity 

This parameter determines the overall aerosol content of the air. As an example, a moist day will have higher turbidity values than a dry day. Values range between 1 and 10.

Turbidity 1.0

Turbidity 4.0

Turbidity 10.0

 

Also note that turbidity affects the look of the sun when near the horizon. The following renders show the effect of turbidity for different sun elevations.

 

Elevation = 0.75
Elevation = 0.50
Elevation = 0.25
 Turbidity 6.0Turbidity 7.0Turbidity 8.0

 

 

Ground Color 

Changing ground color (also called albedo) affects the brightness of the whole sky-dome, especially in high turbidity settings. High albedo values can occur in winter scenes - snow reflectance is very bright so almost all incident radiation is reflected and backscattered towards the viewer.

Ground Color is white

Ground Color is green

Ground Color is blue

Elevation

This the elevation of the sun, in degrees. The range is 0 to 90.

Elevation 5

Elevation 20

Elevation 40

Azimuth 

This is the azimutal position of the sun, in degrees. Range is 0 to 360.

Azimuth 90

Azimuth 180

Azimuth 270

Sky Tint

A convenient artistic control to change the overall color of the sky dome. If physically correct renders are desired this parameter should be set to (1,1,1).

Sky Tint is white

Sky Tint is red

Sun Tint

A convenient artistic control of the sun's color. If physically correct renders are desired this parameter should be set to (1,1,1).

Sun Tint is white

Sun Tint is red

Sun Size

The size of the sun in the sky, in degrees. The default value (0.51 degrees) is the size of the sun as seen on earth. Note that changing the size of the sun doesn't affect the overall radiance of the sky in this model but the objects will receive more light, as seen in the images below.

Sun Size 0.51 (default)

Sun Size 1.51

Sun Size 3.51

Draw Sun Disk

This enables or disable the sun in the sky. Disabling the sun will disable the drawing of the sharp component of the shadows (the strongly directional shadow).

Draw Sun Disk is on

Draw Sun Disk is off

Draw Ground

Draws the ground (the space under the horizon) using the color specified in Ground Color.


Quick Start and Example Scene

 

 

 

 

An example Maya scene can be found here: sky-example.ma

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