VRay for Rhino Manual

Lighting plays the key role in the rendering process. You simply can't get a good rendering result without a good lighting environment.

Same as the real space lighting, light sources are divided into direct and indirect lighting. Direct lighting is using the light command to create Rectangular Light, Omni Light, Spot Light and Parallel Light and use directly on the object. Indirect lighting refers to any lighting which is from bouncing light, or an environment.

Let's do a test

Open file: Cup Illumination-01.3dm, there is not any light in the scene. Light source is from Environment light.

1. So far the cup and ground are using the same Val230 off white color. Render it with GI default setting to 1 and get the result as the image shown below.

2. Increase the GI value to 2 without changing the color, the result is shown below.

3. Do not change the GI value and change the Brightness to Val127 under the Texture Editor. Render it again and the result is very close to the first image on the top.

The reason for doing this test is to let users understand the importance between lighting and material. Should the lighting be adjusted to accommodate material or should material be adjusted to accommodate lighting?

It is clear from the previous example that the lighting must be adjusted to accommodate materials. With the second image from the previous test if we created another material and inserted into the scene, it would not render how we created it.

Here’s another example. Lets take the shirt that you’re wearing right now. What color is it? If you walked into a closet with no light, what would the color of your shirt be? The answer is that the color of your shirt would be the same, BUT it would appear different based on the lighting environment. This is why you should adjust your lighting to achieve the desired affect, as opposed to changing the materials.

With an incorrect lighting environment, such as the second part of the example above, it will be very hard to predict how your scene will react. When adding an new material, it will not look how it did when you created it, thus making it harder to achieve the original intended appearance for the material. Incorrect lighting also has an adverse affect on other aspects of your rendering and may affect shadows, reflections, and even make your rendering take longer than it should. Now you see why having a proper lighting solution is very important.

Interior or Exterior?

When facing the task of illumination, separate it into interior illumination and exterior illumination. Here exterior means open space. For example, place an object on the ground without any walls around it to block the light. It's easier to adjust illumination for open space. Interior means light source is blocked by wall or other similar objects in the scene; an enclosed space in which the environment light will not have the direct effect to the object. Or maybe some openings on the wall or windows allow part of environment light comes through them. Interior lighting is generally more complex than exterior lighting.

The image below shows open space illumination and the second image below shows the semi-open space illumination.

The image below shows the same semi-open space but add one more opening to the wall. The brightness increased due to second opening added to the wall. The second image below shows different locations for openings also affect the brightness of the scene.

Techniques for adjusting illumination

Before rendering a scene, try to finish all the modeling as this greatly simplifies the task of adjusting the illumination. The number of objects, object location, material type, color and even size will all affect the illumination in some way.

When beginning to create the lighting solution it is important to have a solid base in which to begin evaluating how you will need to light your scene, as well as how it will react to lighting. With V-Ray this task is very easy because of how the environment light works. Basically, with your environment color set to white (255,255,255) and the intensity set to 1, you should get a neutral lighting of your scene. This is useful in that it will allow you to properly assess the appearance of your materials, as well see if there are any areas of your scene which will naturally receive more or less light from the environment.

Now lets see this in action. Open file Cup-Illumination-01.3dm again. This is a easy open space example, there is no light added to the scene, and the Environment color and intensity are currently set to Val 255 and 1 respectively.

Using a white floor color is important as it will show the most amount of light that will effect the scene. This is because white allows the most amount of light energy to be retained after it bounces off a surface. With the white floor, we know that if we change its material to something that is darker, than we can expect a little less bounced light in our scene. In an exterior scene like this one the effect is minimal, but when creating an interior illumination solution this is an important thing to know.

1. Assign the Val 230 color to floor, R191 G19 B19 red color to cup first, render it and result as below.

2. Re-assign the R255 G100 B100 red color to the cup and render; you will get the result as below.

From the two images above we can see the colors for the floor and cup are rendered very close to actual colors, which means the Environment lighting is set to correct intensity and brightness for creating good illumination. Otherwise, if the intensity is too strong, it will make the floor and cup appear brighter that the values that we set when we made the material.

Now that we have a good render we can begin the task of adding more lighting into the scene. Depending on what you are trying to create this may only required one additional light (the sun perhaps) or many lights. The important thing to remember is that the lighting must be balanced. Since we already have a scene which would become overly bright, or burned as it is sometimes called, if any additional light is added there must be a compromise between the different lights. In most cases this will mean that the environment intensity will be decreased, but the ratio between environment lights and other lights is something that you must determine. Try out different options; one where the environment light is stronger than other lights, and another where other lights are stronger than the environment.

HDR Environment light

Instead of using a color for an Environment light source, V-Ray also supports HDR images to use as Environment light source. Open file Cups-HDR.3dm.

1. Open V-Ray for Rhino's Render Options, open Environment menu and click on the "m" at the right of GI to enter the Texture Editor.

2. Choose Bitmap from Type, click on "m" beside File and import an .hdr file.

3. Because the textures is being applied to the environment and not an object make sure you check the Environment under UVW after the file is imported.

Render it and will get the image below. You will see a big difference between this image and the image that used only color for Environment light source. This is because the HDR is providing the illumination for the scene based on the colors and intensities of the image.

4. If you want the object reflect the HDR image Environment as well, you can assign the same HDR image to the Environment Background, and make sure the UVW is set to Environment. After the Background HDR is added, the result is as the image below.

To compare, below are three images rendered with different HDR images as the Environment light sources. You can see the light and color change dramatically according to each HDR image.

Bitmap Environment light source

If the user does not have HDR image, a regular Bitmap can be also used as Environment light source. Although a normal Bitmap doesn't have the same ability to create as dynamic an environment, normal images are very easy to get. As long as you pick the right Bitmap and control the Intensity well, it can still be a very good Environment light source.

The three images below are rendered with a different Bitmap. If you compare them to image rendered with HDR images, it is not as easy to determine the direction of the light and the shadows are not very clear.

Environment light source for semi-open space

We used open space to discuss Environment light source for last example . Now is time to use semi-open interior space for this example to see differences between interior and exterior illumination.

Open file: GI Environment-01.3dm. In the scene is a enclosed cube with an open on the right. There are some objects placed on the wall next to the opening wall and there is no light in the box. All objects used Val190 gray color, current GI Intensity is 2, color is light blue. Render it and you will get the almost black image as below. The result is due to no light in the scene and only a small opening allows the Environment light come in.

Increase the GI Intensity to 4 and render it again. The result is as below, a little bit brighter this time.

Increase the GI to 8 and render again. The result is closer to reasonable illumination.

This example shows that Environment light in semi-open spaces usually doesn’t lead to a proper solution the first time.

When beginning to set up the illumination for interior space, a first step should be to check how many openings in the scene allow environment light to come in. This includes transparent objects like windows or doors. It is also important to know how many lights are intended to be in the final scene, as well as what time of day the rendering is meant to depict. These are all very helpful for setting the Environment light correctly.

Even if the Environment lighting is set to the desired level for the final scene, you will still wind up having to adjust it based on the materials and other lights that will be added to the scene. Very often the camera got moved during this process and the quality and brightness are not what you were expecting. Even though the interior lighting is under control, once the camera is pulled out from the box, you will get the bright white rendered result as the image below.

It will still be necessary to add light in the room, adjust the brightness and render as the second image below.