SunLight

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

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.

UI Path

It is 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.

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.

Example: Intensity Multiplier

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

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: Size Multiplier

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).

Size multiplier

= 4.0

Size multiplier

= 10.0

Size multiplier

= 40.0

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. See the New PRG Clear Sky Altitude, Turbidity, and Nautical Twilight Effect examples below.

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

Altitude – Controls the observer's altitude in meters. As the altitude increases, sky clarity improves, and the horizon line becomes less defined.

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 Value example below.

Example: PRG Clear Sky New - Altitude

This example shows how the Altitude values affect the visualization of the sky. Higher Altitude values result in better sky clarity and a less defined horizon line.

Altitude

= 0

Altitude

= 1000

Altitude

= 2000

Altitude

= 10000

Altitude

= 15000

Example: PRG Clear Sky New - Turbidity

In this example, you can see how the amount of dust in the air affects the color of the sun and sky. Smaller values produce a clear image, while higher values dim the sun and sky.

Turbidity

= 2

Turbidity

= 2.6

Turbidity

= 3

Turbidity

= 4

Turbidity

= 5

Example: PRG Clear Sky New - Nautical twilight effect

This example shows how the sun's position affects the sky, creating a twilight effect. Changing the sun's position could require adjusting the Exposure Value as well.

Exposure Value

= 10;

Sun below the horizon

= 0°

Exposure Value

= 10;

Sun below the horizon

= -2°

Exposure Value

= 10;

Sun below the horizon

= -4°

Example: Turbidity

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. Enabled: on, Intensity multiplier: 0.01, Size multiplier: 1.0

Turbidity

= 2.0

Turbidity

= 4.0

Turbidity

= 8.0

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

Night Sky

Simulates a realistic procedural night sky, complete with the Moon, stars, and the Milky Way. As part of the Sun and Sky system, Night Sky allows users to create accurate nighttime environments based on real-world positioning.

The location and time used to position the stars and the moon are determined by the host application. They can be manually defined using the Custom Location and Time parameters.

Stars

Enabled – Enables the appearance of stars and the Milky Way in the night sky.

Size Multiplier – Controls the size of the stars. A default value of 1 renders the stars with radius of 1 pixel, a value of 2 makes the stars twice as large. If set to 0 the stars are rendered with the minimum size possible.

Size Difference Mult – Controls the size difference between faint and bright stars. When set to 0, all stars have the same size, and a value of 1 makes the brightest stars twice as large, the second magnitude stars (e.g. Polaris) keep their size, and the faintest stars disappear.

Direct Light Mult – Controls the brightness of the directly visible stars in the sky or in perfect mirror reflections/refractions. See the Stars Direct Light example below.

Indirect Light Mult – Controls the brightness of the scene illumination caused by the stars. See the Stars Indirect Light example below.

Milky Way Mult – Amplifies the brightness of the Milky Way.

Example: Stars Direct Light

The Direct Light parameter controls the brightness of the stars in this example.

Brightness = 0.5

Brightness = 1

Brightness = 2

Example: Stars Indirect Light

The Indirect Light parameter controls the intensity of the stars in this example.

Intensity = 1

Intensity = 4

Intensity = 8

Moon

Enabled – Enables the appearance of the Moon in the night sky.

Size Multiplier – Controls the visible size of the Moon. Affects the appearance of the Moon disc as seen by the camera and reflections, as well as the blurriness of the Moon shadows.

Direct Light Mult – Controls the brightness of the Moon as seen directly in the sky or in perfect mirror reflections/refractions. See the Moon Direct Light example below.

Indirect Light Mult – Controls the brightness of the scene illumination cast by the Moon. See the Moon Indirect Light example below.

Glow Multiplier – Controls the brightness of the glow around the Moon. A value of 0 disables the glowing effect.

Filter Color – Specifies the moonlight color. The default white (1, 1, 1) color means no change of color.

Custom Azimuth – Specifies the Moon azimuth angle measured from the scene North to Eastward. A value of 90 aligns with the X-axis (Solid red line) or East.

Custom Elevation – Controls the angle between the Moon and the ground. A value of 0 makes the Moon to be exactly at the horizon, and a value of 90 makes the Moon in the zenith.

Custom Phase – Specifies the phase of the Moon, where a value of 0 is full Moon, 90 is first quarter, 180 is new Moon, and 270 the last quarter. See the Phase example below.

Custom Rotation – Rotates the Moon disc in the sky, where 0 makes it match the Moon appearance in its highest point when observed in the Northern hemisphere, and 180 corresponds to the Southern hemisphere.

Example: Moon Direct Light

This parameter controls the brightness of the moon in this example.

Direct Light Mult = 0.025

Direct Light Mult = 0.05

Direct Light Mult= 0.01

Example: Moon Indirect Light

This parameter controls the intensity of the moon in this example.

Indirect Light Mult = 0.25

Indirect Light Mult = 0.5

Indirect Light Mult = 1

Example: Phase

This example shows how the Phase parameter controls the Phases of the moon where 0 is full moon and 180 is new moon.

Phase = 0

Phase = 90

Phase = 180

Custom Location and Time

Enabled – When enabled, the location and time used to position the stars and the Moon can be manually defined. When disabled, they are determined by the host application.

Lat / Long – Specifies the latitude and longitude of the location used to position the stars.

Day / Month / Year – Specifies the date used to position the stars.

Hours / Min / Sec – Specifies the time used to position the stars.

Time Zone – Specifies the time zone applied to the time used to position the stars.

Daylight Saving Time – Determines if DST is applied to the time used to position the stars.

North – Specifies the North vector direction.

Ground

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 Cloud Density example below.

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

Thickness (m) – Controls the clouds thickness. See the Cloud 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 (%).

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 Ground Shadows example below.

Example: Cloud Density

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

Density

= 0

Density

= 0.4

Density

= 0.8

Example: Clouds Variety

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

Variety

= 0

Variety

= 0.5

Variety

= 1

Example: Cirrus Amount

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

Cirrus Amount

= 0

Cirrus Amount

= 0.5

Cirrus Amount

= 1

Example: Cloud Height

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

Height

= 500

Height

= 1000

Height

= 1500

Example: Cloud Thickness

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

Thickness

= 200

Thickness

= 500

Thickness

= 800

Example: Ground Shadows

This example shows the effect of the Ground Shadows option.

Ground Shadows

= Off

Ground Shadows

= On

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 through 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.

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.

Contrails Number

= 5

Contrails Number

= 20

Contrails Number

= 40

Example: Contrails Strength

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

Contrails Strength

= 0.1

Contrails Strength

= 0.5

Contrails Strength

= 1

Example: Contrails Distortion

The Contrails distortion parameter is used to add variety to the trace line.

Contrails Distortion

= 0.1

Contrails Distortion

= 0.5

Contrails Distortion

= 1

Example: Contrails Offset

The Contrails offset option introduces an offset along the X or Y direction in the sky.

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 from 0 to 2.0, in steps of 0.2.

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 rotates this vector clockwise.
Wind Speed (m/s) – Specifies the cloud's movement speed measured in meters per second.
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

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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 Proceedings;
  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