Example 1: Single-sided vs Double-sided lights

Example 2: Size of lights, shadows and intensity

Example 3: Real-world lights have inverse-square falloff

Example 4: Skylight, self-illuminated panels and VRayLights

Example 5: IBL (Image-Based Lighting)

## Example 1: Single-sided vs Double-sided lights

This example demonstrates the difference between a single-sided and a double-sided planar rectangular light:

 Double-sided is off Double-sided is on

## Example 2: Size of lights, shadows and intensity

The following images show how the size of a light affects shadows. Bigger lights produce blurrier shadows, while smaller lights produce sharper shadows:

 Radius = 2 Radius = 4 Radius = 6 Units = default   Intensity mult = 100 Units = Lumens   Intensity mult = 800 Units = lm/m/m/sr   Intensity mult = 5 Units = Watts   Intensity mult = 1 Units = W/m/m/sr   Intensity mult = 0.008

Notice that when we set the Units to Watts and Lumens the light appears to be of the same intensity. This is because the emmited light does not depend on the size of the light. The other three units depend on the size of the light - larger surfaces emit more light, that is why the intensity of the light increases with the radius of the light source. Note that the Intensity multiplier had to be adjusted for the different units in order to produce similar light intensity in the first images. However the multiplier is the same for each set of three images.

## Example 3: Real-world lights have inverse square falloff

The following images demonstrate the No decay parameter. In the real world the light sources attenuate with the inverse square of the distance from the light to the shaded surface. However you can disable light decay to achieve a light with constant intensity. The settings for the light source are the same for both images with the exception of the Decay parameter:

 No decay is off (default) No decay is on

## Example 4: Skylight, self-illuminated panels and VRayLights

Here is an example of a simple room where the light comes from the environment. The scene was rendered in several different ways:

• with just environment skylight with irradiance map as a primary engine;
• with a self-illuminated panel at the window, again with the irradiance map as a primary engine;
• with a VRayLight at the window and the irradiance map as a primary GI engine;
• with just environment skylight but with brute force GI as a primary engine.

In all cases, the Light cache was used as a secondary GI engine. The environment, the self-illuminated panel, and the VRayLight all have the exact same color and multiplier.

 Environment light (skylight) only Self-illuminated panel at the window VRayLight at the window Environment light (skylight) only and brute force GI

As you can see, all methods produce the same light distribution, but there is a difference between render times and quality.

In the first two cases, we rely on the irradiance map to capture the lighting coming from the window. The result is very similar, as well as the rendering times. Since the irradiance map is a blurry method, the shadows come out a little blurred. Although we can reduce the blurring by using higher irradiance map settings, this will cost us additional render time.

In the third case, since we use a VRayLight, the shadows come out very sharp and nice, and the rendering time is reduced. This is because the irradiance map was calculated much faster - in the previous two cases, it had to trace a lot of rays to sample the window accurately.

In the fourth case, we used brute force GI instead of the irradiance map. This produces sharp shadows too, since the brute force GI is a non-blurry GI method. However, render time has increased quite a lot.

In this exampe, using a VRayLight produces the best result in the shortest time. However, if you need to have many lights, this method can become quite slow, since every single light needs to be sampled.

## Example 5: IBL (Image-Based Lighting)

IBL (image-based lighting) is a new feature, provided by the V-Ray renderer.

The V-Ray dome light has been extended to support arbitrary texture maps that determine the amount of light coming from each direction on the virtual dome hemisphere. V-Ray then uses importance sampling to trace more rays in the directions where most of the light is coming from. This ensures speed and quality that were never before possible with pure gathering GI methods.

• Easy setup for image-based lighting (IBL);
• Importance sampling of the dome texture for fast and clean results;
• Support for photon mapping for fast and accurate caustic effects.

In the following example we will show how this works with an HDR image.

 Initial position of the dome-light. Y axis is perpendicular to the ground plane. Rendered image Position 1 This time the dome is rotated along its Y axis to 90 degrees. Notice this has no effect, as the dome is using the same part of the HDRI. Rendered image Position 2 The dome is rotated along its X axis to 90 degrees. Now the dome uses another part of the HDRI. Rendered image

Now we are going to show how rotating the HDRI can also affect the rendered image.

We will rotate the HDRI from the Hypershade by selecting the VRayPlaceEnvTex node.

 The default position of the Dome Light. Rotating the HDRI to -90 degrees. Now the dome obviously uses some of its the darker areas. Rendered image

This time we will rotate the map in the oposite direction.

 The default position of the Dome Light. Rotating the HDRI to 90 degrees. Now the dome obviously uses some of its brighter areas. Rendered image

We will go further, adding some vertical rotation to the HDRI.

 The default position of the Dome Light. Adding 90 degrees vertical rotation to the HDRI. See how light and shadows have changed a lot. Rendered image

When you are using Dome Light the intensity multiplier scroll will not have any affect on the brightness of the light. In order to change the brightness you will need to use the color balance options for the texture. The brightness can be controlled through the Value atribute of the Color gain parameter in the Color Balance rollout. To demonstrate this we have reset the horizontal and vertical rotation of the hdri to 0.0 and rendered two images - one with value set to 0.5 and one with value set to 2.

 Rendered image Rendered image