VRay for 3ds Max Manual

VRaySun and VRaySky Parameters

	General
	VRaySun parameters
	VRaySky parameters
	Notes
	Links and references

Search keywords: sun, sky, VRaySun, VRaySky, environment, daylight, sunlight, exterior lighting

General

---

The VRaySun and VRaySky are special features which are provided by the V-Ray renderer. Developed to work together, the VRaySun and VRaySky 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 VRaySun.

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 Links and references section.

VRaySun parameters

---

The VRaySun is located in the (Create - Lights - VRay) panel. You can also specify the VRaySun as the sun type inside a 3ds Max Daylight system.

Enabled - turns on and off the sun light.

Invisible - when on, this option makes the sun invisible, both to the camera and to reflections. This is useful to prevent bright speckles on glossy surfaces where a ray with low probability hits the extremely bright sun disk.

Turbidity - this parameter determines the amount of dust in the air and affects the color of the sun and sky. Smaller values produce a clear and blue sky and sun as you get in the country, while larger values make them yellow and orange as, for example, in a big city. For further info, please see the Examples section.

Ozone - this parameter affects the color of the sun light. Available in the range between 0.0 and 1.0. Smaller values make the sunlight more yellow, larger values make it blue. For further info, please see the Examples section.

Intensity multiplier - this is an intensity multiplier for the VRaySun. Since the sun is very bright by default, you can use this parameter to reduce its effect. See the Notes and Examples sections for more information.

Size multiplier - this parameter controls the visible size of the sun. This affects the appearance of the sun disc as seen by the camera and reflections, as well as the blurriness of the sun shadows. For further information, please see the Examples section.

Shadow subdivs - this controls the number of samples for the area shadow of the sun. More subdivs produce area shadows with better quality but render slower. For further info, please see the Examples section.

Shadow bias - moves the shadow toward or away from the shadow-casting object (or objects). If the bias value is too low, shadows can "leak" through places they shouldn't, produce moire patterns or making out-of-place dark areas on meshes. If bias is too high, shadows can "detach" from an object. If the bias value is too extreme in either direction, shadows might not be rendered at all. For further info, please see the Examples section.

Photon emit radius - determines the radius of the area, in where photons would be shot. This area is represented by the green cylinder around the Sun's ray vector. This parameter has effect when photons are used in the GI solutions or caustics.

Exclude - this button allows you to exclude objects from illumination/shadow casting for the sun light.

VRaySky parameters

---

The VRaySky texture map is typically used as an environment map, either in the 3dsmax Environment dialog, or in one of the slots of the V-Ray Environment rollout and behaves very much like a HDRI environment map. The VRaySky changes its appearance based on the position of the VRaySun.

Manual sun node - specifies how the VRaySky detemines its parameters: 

Off - the VRaySky will automatically take its parameters from the first enabled VRaySun in the scene. In this case, none of the other parameters of VRaySky are accessible.

On - you can choose a different light source. It is recommended that you choose only direct lights, as the vector for the direction is taken into consideration when computing the appearance of the sky. In that case the VRaySun is no longer controlling the VRaySky and the parameters in the texture map rollout determine the final look of the sky.

Sun node - specifies which light source is chosen if Specify sun node is On.

Sun turbidity - refer to VRaySun parameters

Sun ozone - refer to VRaySun parameters

Sun intensity multiplier - refer to VRaySun parameters

Sun size multiplier - refer to VRaySun parameters

Sun invisible - when this option is on, the sun disk will not be visible on the sky texture.

Notes

---

• By default, the VRaySun and VRaySky 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. You can either use Color mapping to bring these values to a smaller range (which is the preferred way) or you can use the Sun intensity multiplier to make the sun and sky less bright. Using the VRayPhysicalCamera with suitable values also produces a correct result without changing the sun and sky parameters.

Links & references

---

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, B. Smits, "A Practical Analytic Model for Daylight", Siggraph 1999, Computer Grahics Procedings; this paper includes source code examples and is the base for the VRaySun and VRaySky plugins.
   
• The intensity of solar radiation; this page contains information about the average intensity of the solar radiation, as well as some specific measurements.
   
• Total Watts emitted by Sun; Solar Irradiance; these pages contain a list of accurate solar irradiances across a large portion of the electromagnetic spectrum.
   
• Distance from the Earth to the Sun; size of the Sun; among other things, this document gives the distance from the Sun to the Earth and the size of the Sun derived from astronomic observations.