This page provides information on the V-Ray Sun Light and V-Ray Sky.
The V-Ray Sun and V-Ray Sky are special features which are provided by the V-Ray renderer. Developed to work together, the 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 the V-Ray Sun. The direction of the Sun is marked with an arrow in the Rhino viewport.
The V-Ray Sun and Sky are based largely on the SIGGRAPH '99 paper "A Practical Analytic Model for Daylight" by A. J. Preetham, Peter Shirley, Brian Smits. For a more complete list of references, please see the References and links section.
The Sun is commonly used in ArchVis projects. If the project default settings are set to ArchVis through vrayChangeDefaultScene command, the Sun has to be turned on. For more information see the vrayChangeDefaultScene command.
||V-Ray Asset Editor|| > Lights > SunLight
Enable/Disable the SunLight by clicking on the icon.
||V-Ray Toolbar|| > V-Ray Lights Tab > SunLight
Left-click the Sun icon to open the Sun creation panel.
Right-click the Sun icon to show the Sun panel.
Enabled () – Turns SunLight on and off.
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.
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.
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.
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.
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.
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.
Example: The Size Multiplier Parameter
Common settings in this example are Turbidity: 3.0. 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).
Example: The Turbidity Parameter
This example is done with the default Sun settings, except for the Blend Angle: 10. It demonstrates the effect of the Turbidity parameter. Generally, it 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, EV: 14,48 (default).
Example: Ozone Value
The default Sun settings are used for this example. The Ozone parameter affects only the color of the light emitted by the sun. Notice how the 0 value gives an overall yellowish contribution of the light to the scene, while a value of 1 is in the blue spectrum.
Invisible – When enabled, the sun becomes invisible to both the camera and reflections. This is useful to prevent bright speckles on glossy surfaces where a ray with low probability hits the extremely bright Sun disk.
Shadows – When enabled (the default), the Sun casts shadows. When disabled, the light does not cast shadows.
Affect Diffuse – When enabled, the V-Ray Sun affects the diffuse properties of the materials.
Affect Specular – When enabled, the V-Ray Sun affects the specular of the materials.
Caustic Subdivisions – Determines the number of caustic photons emitted from the light source. Lower values mean more noisy results but render faster. Higher values produce smoother results but take more time.
Photon Emit Radius – Defines the area around the V-Ray Sun from where the photons are shot.
By default, the 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 produced 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 VRayPhysicalCamera with suitable values also produces a correct result without changing the sun and sky parameters.
Here is a list of links and 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 http://www.cs.utah.edu/~shirley/papers/sunsky/
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
This document is available at http://www.jgsee.kmutt.ac.th/exell/IntensitySolarRad.pdf
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