This page provides information on V-Ray Sun Light and V-Ray Sky.

See the Improved Sun and Sky page or the Courseware page for more information.

 

Overview

V-Ray Sun and V-Ray Sky are special features which are provided by V-Ray renderer. Developed to work together, V-Ray Sun and V-Ray Sky reproduce the real-life Sun and Sky environment of the Earth. Both are coded so that they change their appearance depending on the direction of V-Ray Sun.

The V-Ray Sun and Sky are based largely on SIGGRAPH '99 paper "A Practical Analytic Model for Daylight" by A. J. Preetham, Peter Shirley, Brian Smits. For a complete list of references, please see the References section.

Sun light has some unique qualities:

  • Sun light rays that strike the scene objects are treated as parallel to one another regardless of how far the Sun object is placed from the scene objects, producing the parallel shadows that our own sun creates.
  • Sun light is designed to be used with global illumination. When the light bounces around the scene, the resulting rendering looks like sunlight in real life.
  • If you are using GI, use Sun light with Sky environment background to provide realistic lighting and coloring for the scene. Often, Sun/Sky is the only lighting setup needed in the scene to produce a photoreal rendering.
  • The Sun/Sky combination is suitable for an exterior scene or for an interior scene with windows or other openings through which the light comes.

Animating V-Ray SunLight is only possible if the time and date of different scenes in SketchUp differ. The time and date are set via SketchUp's own Shadows toolbar.

Note that if the SunLight in the V-Ray Asset Editor has its Custom Orientation enabled, it overrides the position set by SketchUp and thus, appears the same for each frame.




UI Path

Created by default. You can change its settings from the Asset Editor:

||V-Ray Asset Editor|| > Lights > SunLight

 

 

 

 

Parameters

Enabled () – Turns SunLight on and off.

Custom Orientation

Custom Orientation – Enables custom orientation.

Horizontal Angle – Controls the custom sun azimuth angle (horizontal rotation).

Vertical Angle – Controls the custom sun altitude angle (vertical rotation).

 

 

Color and Intensity

Color – Shifts the hue of SunLight system towards the color specified in the field.

Color Mode – Affects the way the color in the Filter color parameter affects the color of the sun.

Filter – Shifts V-Ray sun's hue according to the Filter Color parameter. 
Direct – Sets the color of V-Ray sun to the color in the Filter Color parameter. The intensity of the light no longer depends on the position of V-Ray Sun in the sky. Instead, intensity is controlled through the Intensity Multiplier. 
Override – Sets the color of V-Ray sun to the color in the Filter Color parameter. The intensity of the light still depends on the position of V-Ray Sun in the sky.

Intensity Multiplier – Affects the brightness of the sun and can be used to reduce the default brightness. See Notes for more information. See the Intensity Multiplier example below.

Size Multiplier – Affects the visible size of the sun. This includes the appearance of the sun disc as seen by the camera and of the reflections, as well as the blurriness of the sun shadows. See the Size Multiplier example below.

 

 

Sky

Sky Model – Specifies the procedural model that is used to generate V-Ray Sky texture.

Preetham et al. – V-Ray Sky procedural texture is generated based on the Preetham et al. method.
CIE Clear – V-Ray Sky procedural texture is generated based on the CIE method for clear sky. 
CIE Overcast – V-Ray Sky procedural texture is generated based on the CIE method for cloudy sky.
Hosek et al. – V-Ray Sky procedural texture is generated based on the Hosek et al. method.
PRG Clear Sky – V-Ray Sky procedural texture is generated based on the PRG Clear Sky method which has enhanced sunrise and sunset sky.

Horizon Illum. – Specifies the intensity (in lx) of the illumination on horizontal surfaces coming from the sky.

Turbidity  – Determines the amount of dust in the air and affects the color of the sun and sky. Smaller values produce a clear, blue sky and sun as seen in rural areas, while larger values make them yellow and orange as seen in big cities. This parameter is inactive when the Sky Model is set to PRG. See the Turbidity example below.

Ozone – Affects the color of the light. Values closer to 0.0 make the sunlight yellow, and values closer to 1.0 make it blue. This parameter is inactive when the Sky Model is set to PRG. See the Ozone example below.

 

 

 

Albedo Color

Albedo Color – Sets the ground color of the V-Ray Sun and Sky system.

Blend Angle – Specifies the angle in degrees where blending occurs between the horizon line and sky. Values close to 0.0 produce a sharper horizon line, while larger values produce a softer horizon line.

Horizon Offset – Allows the user to manually lower the horizon line. 

 

 

Clouds

Clouds () – Enables the clouds.

Density – Controls the clouds density. A higher value leads to more clouds. See the Density example below.

Variety – Controls the cloud variety in space and shape. See the Variety example below.

Cirrus Amount – Controls the amount of high-altitude cirrus clouds. See the Cirrus Amount example below.

Height (m) – Controls the clouds height. See the  Height example below.

Thickness (m) – Controls the clouds thickness. See the Thickness example below.

Offset X (m) – Controls the offset in the X direction measured in meters.

Offset Y (m) – Controls the offset in the Y direction measured in meters.

Phase X (%) – Clouds phase in X direction specified in percentage (%).

Phase Y (%) – Clouds phase in Y direction specified in percentage (%).

Note that the phase loops every 100 % meaning that values of 0, 100, 200 etc. for Phase X and Phase Y will produce identical results.

Ground Shadows – Enables the clouds shadows, best suited for larger scenes. Note that it is recommended to use a Dome light with a Sky texture for high quality shadows. When disabled, a single shadow is cast over the entire scene depending on whether the sunlight reaching the camera position is blocked by a cloud. Disabling ground shadows is recommended for smaller scenes and may speed up the render process. See the Clouds Shadows example below.

 

 

 

 

 

 

Contrails – When enabled, plane contrails are simulated in the sky.

Contrails Number – Determines the number of contrails generated. See the Contrails Number example below.
Contrails Strength – Determines the opacity of the contrails. Lower values create less opaque trails, which look older. See the Contrails Strength example below.
Contrails Distortion – Determines the amount of distortion in the contrails. See the Contrails Distortion example below.
Contrails Offset X (m) – Offsets the contrails by a given value. See the Contrails Offset example below. 
Contrails Offset Y (m) – Offsets the contrails by a given value.
Contrails Pace (%) – Determines how fast airplane contrails progress along the sky. A value of 100% represents an approximate airplane speed of 800km/h. A value of 0% makes the contrails static. Increasing this multiplier value makes contrails appear faster and persist in the sky for a shorter amount of time. See the Contrails Time example below.


The Dynamic Clouds option has to be enabled to achieve animated contrails.


 

 

 

Dynamic Clouds – Enables the automatic clouds formation. When enabled, the clouds use unique offset and phase values based on the current time of the day.

Wind Direction (deg) – Specifies the wind direction vector rotation in the horizontal plane. A value of 0 means that the clouds move in the positive X direction. Increasing the wind direction value horizontally rotate this vector clockwise.
Wind Speed (m/s) – Specifies the clouds movement speed measured in meters per seconds.
Phase Velocity (%/s) – Specifies the phase change measured in percent of the cycle per second. A value of 1 means that the phase loops to its initial state every 100 seconds. Smaller values result in slower changes and a longer phase loop.

 

 

 

 

Example: Customize the sky with procedural clouds

 

<iframe width="560" height="315" src="https://www.youtube.com/embed/2kz_ZVHmLmQ?list=PLm2Irfq-UvZ1Rh8Tg-PPoYnOq_pKMs9_q" title="V-Ray 6 for SketchUp — Customize the sky with procedural clouds" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

 

 

Example: Direction of the V-Ray Sun Light

Common settings in this example are Turbidity: 3.0, Intensity Multiplier: 0.01, Size Multiplier: 1.0. This example demonstrates the effect of the sun direction. Note how in addition to the scene brightness, the sun position also changes the appearance of the sky and the sun light color.

Example: The Size Multiplier Parameter

Common settings in this example are Turbidity: 3.0, Intensity multiplier: 0.01. This example demonstrates the effect of the Size multiplier parameter. Notice how changes in this parameter affect both the visible sun size and the shadow softness (however overall illumination strength remains the same).

 

 

Sun Z height: 500

Sun Z height: 1600

Sun Z height: 6000 (almost straight above)

 

 

Size multiplier: 4.0

Size multiplier: 10.0

Size multiplier: 40.0

 

 

 

 

Example: The Turbidity Parameter

Common settings in this example are Intensity Multiplier: 0.01, Size Multiplier: 1.0. This example demonstrates the effect of the Turbidity parameter. Generally, this controls the amount of dust particles in the air. Notice how larger values cause the sun and the sky to become yellowish while smaller values make the sky clear.

Example: The Intensity Multiplier Parameter

Common settings in this example are Turbidity: 3.0, Size Multiplier: 1.0

 

 

Turbidity: 2.0

Turbidity: 4.0

Turbidity: 8.0

Height Z: 0, Intensity Multiplier: 0.01

Height Z: 0, Intensity Multiplier: 0.03

Height Z: 0, Intensity Multiplier: 0.05

Height Z: 500, Intensity Multiplier: 0.01

Height Z: 500, Intensity Multiplier: 0.03

Height Z: 500, Intensity Multiplier: 0.05

 

 

 

Example: Ozone Value

Common settings in this example are Turbidity: 2.0, Intensity Multiplier: 0.01, Size Multiplier: 10.0. The Ozone parameter affects only the color of the light emitted by the sun.

 

 

Ozone: 0.0

Ozone: 0.5

Ozone: 1.0

 

 

 

Example: Clouds Density

The Density parameter controls the amount of clouds in the sky. The higher the value, the higher the amount of clouds appearing in the render.

Example: Clouds Variety

This example shows the effect of the Variety parameter on the clouds' distribution and look.

 

 

Density: 0

Density: 0.4

Density: 0.8

Variety: 0

Variety: 0.5

Variety: 1

 

 

 

 

Example: Clouds Shadows 

This examples shows the effect of the Ground Shadows option.

 

 

 

 

 

Example: Cirrus Amount

This example shows how increasing the Cirrus Amount increases the appearance of the cirrus clouds in the render.

Example: Clouds Height

This example shows how the clouds change their position in the sky with increasing the Height value.

 

 

Cirrus amount: 0

Cirrus amount: 05

Cirrus amount: 1

Height: 500

Height: 1000

Height: 1500

 

 

 

Example: Clouds Thickness

The Thickness parameter specifies how full the clouds are. Smaller values make them thinner and sheerer, while higher values make them look heavy. 

 

 

Thickness: 200

Thickness: 500

Thickness: 800

 

 

 

 

Example: Number of Contrails

Note that the contrails are spread randomly across the sky. In most cases, the camera does not capture all of the contrails.

Example: Contrails Strength

This example shows how the strength parameter makes the contrails more visible and prominent in the sky.

 

 

Number of contrails: 5

Number of contrails: 20

Number of contrails: 40

Contrails strength: 0.1

Contrails strength: 0.5

Contrails strength: 1.0

 

 

 

 

Example: Contrails Distortion

The Contrails distortion parameter is used to achieve some variety in the trace line. Move the slider to see the example renders.

Example: Contrails Offset

The Contrails offset option introduces an offset along the X or Y direction in the sky. Move the slider to see the example renders.

 

 

Contrails distortion: 0.1

Contrails distortion: 0.5

Contrails distortion: 1.0

Contrails offset: X 0, Y 0

Contrails offset: X 5000, Y 0

Contrails offset: X 0, Y 5000

 

 

 

Example: Contrails Pace

The frames in this animation show the Contrails Pace parameter with values ranging between 0 and 2.0, with a step of 0.2.

 

 

 

 

 

 

Options

Invisible – When enabled, the sun becomes invisible to both the camera and the reflections. This is useful to prevent bright speckles on glossy surfaces where a ray with low probability hits the bright Sun disk.

Shadows – When enabled (the default), V-Ray Sun casts shadows. When disabled, the light does not cast shadows.

Affect Diffuse – When enabled, V-Ray Sun affects the diffuse properties of the materials.

Affect Specular – When enabled, V-Ray Sun affects the specular of the materials.

Affect Atmospherics – Specifies whether the light influences the atmospheric effects in the scene. The value determines the amount of involvement.

Atmospheric Shadows – When enabled, the atmospheric effects in the scene cast shadows.

Caustic Photons

Caustic Subdivisions – Determines the number of caustic photons emitted from the light source. Lower values mean more noisy results but faster rendering. Higher values produce smoother results but take more time.

Emit Radius – Defines the area around the V-Ray Sun from where the photons are shot.

 

 

 

Notes

  • By default, V-Ray Sun and V-Ray Sky are very bright. In the real world, the average solar irradiance is about 1000 W/m^2 (see the References below). Since the image output in V-Ray is in W/m^2/sr, you will typically find that the average RGB values produces by the sun and the sky are about 200.0-300.0 units. This is quite correct from a physical point of view, but is not enough for a nice image. Using the V-Ray Physical Camera with suitable values will produce a realistic result without changing the sun and sky parameters.
  • Procedural Clouds are visually similar to the ones in Enscape by default from 6.00.02 on. When opening scenes saved with an earlier version - 6.00.00 or 6.00.01, there is an Enscape Compatibility parameter which can be enabled to make the Clouds match the Enscape ones. Note that once enabled the checkbox will disappear from the Interface.

 

 

References

Here is a list of references about the V-Ray Sun and Sky implementation, as well as general information about the illumination of the Sun.


  • A.J. Preetham, P. Shirley, and B. Smits, A Practical Analytic Model for Daylight, SIGGRAPH 1999, Computer Graphics Procedings;
    An online version can be found at https://courses.cs.duke.edu/cps124/spring08/assign/07_papers/p91-preetham.pdf
    This paper includes source code examples and is the base for the VRaySun and VRaySky plugins.
  • R. H. B. Exell, The intensity of solar radiation, 2000
    https://www.phenix.bnl.gov/phenix/WWW/publish/barish/publish/wasiko/Copy/Solar/The%20Intensity%20of%20Solar%20Radiation.htm
    This document contains information about the average intensity of the solar radiation, as well as some specific measurements.
  • R. Cahalan, Sun & Earth Radiation
    This page can be found at  http://climate.gsfc.nasa.gov/static/cahalan/Radiation/ (Please note that this link is no longer valid.)
    These pages contain a list of accurate solar irradiances across a large portion of the electromagnetic spectrum.
  • D. Robinson-Boonstra, Venus Transit: Activity 3, Sun & Earth Day 2004
    This document can be found online at  http://sunearth.gsfc.nasa.gov/sunearthday/2004/2004images/VT_Activity3.pdf (Please note that this link is no longer valid.)
    Among other things, this document gives the distance from the Sun to the Earth and the size of the Sun derived from astronomic observations.
  • Hosek L, et al, An Analytic Model for Full Spectral Sky-Dome Radiance
    This document can be found online at http://cgg.mff.cuni.cz/projects/SkylightModelling/HosekWilkie_SkylightModel_SIGGRAPH2012_Preprint_lowres.pdf
    Describes the Hosek sky model used by the VRaySun and VRaySky