Light, Part 1. Introduction to Light

(version September 16, 2007)

These is a short article on the topic of light., and is meant to be an introduction. It covers issues that are important when learning to work in 3D and these issues are often overlooked in discussions.

Importance of Lighting

The digital world allows you create effects in scenes which has no physical world counterpart. To avoid doing this by accident and not because of intent, you should become familiar with the concept of light as it occurs in 3D software.

Learning about light is one of the key ingredients in making a 3D scene. 3D Applications often use a “standard term” in a very specific way in the application. You will find slight variations in the use of the terms here depending on which application you are running. Don’t be alarmed by that, and don’t lose the trust for the program you are running. Instead, step back a bit and learn the terminologies in a general way without specific regard to the programs you are running. Pay attention to the variations among programs in their use of terms. It takes time to learn these differences. And it is only possible by working with many examples. Learning how to control light (location, color, intensity and direction) in your scene will make the difference in having a good job or a great job. The challenges for working with light are very different for an outdoor scene compared to an indoor scene. You will need to make careful lighting choices for your models depending on which 3D software is used to render your scenes. The more sources of light you have in your scene, the longer the render times. In some cases scenes with very bright illumination will take much longer to render, depending on options you choose.

3D software generally has defaults for many of the operations you can control. Typically a 3D application will have default lighting. You will work in one program taking this lighting for granted, then discover to your unpleasant surprise that your model imported into another program does not look as good. Perhaps the changes in default lighting are the reason.

You should work with the lighting throughout the development of your scene. Start off with some appropriate choices, but vary them as you work.

In some 3D applications negative light sources exist: instead of adding to the light at the place where they are directed, they remove or decrease overall lighting at that point in the scene. These can be powerful tools available in the 3D world which are not available to traditional photographers. A 3D designer has many more resources available to himself when working with lights than a photographer has. Another example: you can change the properties of lights and objects to remove the normal property of casting shadows. This, too, is an option not available to traditional photographers.

This section talks about lighting, but it should be remembered that this is only part of the story of how objects look in a scene. Shaders, materials and surface properties of objects (how reflective they are, how translucent they are) will also have impact on the lighting effects you make use of. The start to understanding light is to realize there are two chapters to the story. The first talks about light as such, what controls are common in 3D software. The second chapter talks about how light interacts with surfaces. This is what brings your scenes to life. Take time to learn both chapters and you will find that you can solve a wide range of problems. You will enjoy work to a far greater degree. Have a number of possibilities always at your fingertips, and the problems you bump into will go away faster.

Personal preferences and artistic tastes should be your main guiding principles in working with lighting in 3D software. But it is difficult to understand how to bring about your preferences and tastes until you have experimented with the capabilities of each of the 3D software choices you have available at your fingertips. Prior to planning any long project in a particular choice of 3D software, you should run a series of tests to understanding the lighting choices available to you. For example, create a very simple scene (a ball, a box, a cone for example) and add just one kind of light to it. Practice moving it around. Change the kind of lighting to another type (for example, from a spotlight to a point light) and make the same adjustments. Keep your test scenes around. They may help you solve a problem in a more complex scene when you are not getting the results you need.

In most cases light summons up another complex series of topics about the way that various observers will see your scene. Lighting can open up emotions, which is to say that for some observers your choice of lighting will strongly influence the emotional quality of your scene as they see it. A common objection to digital art created in 3D applications is that the scene is “too harsh” or “too sharp”. Another way of saying this is that 3D can create extremely exact scenes with mathematic precision, bringing out aspects of a scene that our real-life experience or our photographic experience for that matter never comes upon. You should step back from your scene and ask yourself if this is the way it would look in nature, if you are working with a natural scene. This sometimes means that you should not forget to add some haze or fog, more typical of the real world, to your scenes so that everything you do shows a harshness of exact light and reflection.

Regarding this aspect of harshness of the 3D scene, there is an interesting analogy that only makes sense if you have experience non-digital recorded music, such as on LPs or on cassette tapes. When CDs first came about many entrenched listeners objected to the “harsh sound” (these are their actual words) of the digital CD quality. LPs and tapes muffle (i.e. change or reduce the amount of clarity or detail) the sound somewhat and the more the media are used, the greater the effect due to wear on the playing surface. It took some listeners time to adapt to the sharp clarity of digital CD sound and accept it as just as good. One contributing factor here was that CDs could now record much softer and louder passages with less distortion than tapes or LPs, and this aspect annoyed listeners to the new digital CD media. In 3D the analogy to the discussion about light that has been going on in the preceding paragraphs is that you can show a brighter range of light compare to film, and also bring in much lower light than film would every do. Observers of your 3D work may struggle to handle low light or bright light 3D scenes that you create.

When you choose to add lights to a scene, here are some typical choices:
    Sunlight, Ambient Light
    Point Light
    Light Gels
    Rendering Engines
    Volumetric Lights
    Spotlights
    Light Panels
We will talk about each of these choices below and give examples of many of these features.

Vary your choices of lighting when you work on a new project. Do not always settle upon the same types of lighting. You will experiment differently when you are working on a project instead of just a test scene. Learn the subtle differences that exist for each type of light, and do this is each 3D product you work with.

Below are some terminologies which you will encounter in your 3D work. Try to learn the details for each of the main terms. In the long run this will be benefit to you as help you grow as a 3D designer.

Ambient light
Ambient light is a light source which appears to be coming from all around at the same time—it is often simply called indirect light. For example, in photography sunlight on a cloudy day is ambient light: it has the same intensity all around. {Normally sunlight is a directional light and appears as such when it is not a cloudy day.) When speaking of 3D scenes, ambient light provides equal light for every point in the 3D scene; you do not control the direction of the light (because it comes from all around); instead you control color and intensity. Changes in color or intensity will affect the overall scene, changing the color everywhere or changing the intensity to the same degree everywhere. If you add an ambient light to your 3D scene, your software will allow you to change only color and intensity in most cases, not direction. Ambient light will affect all areas of your scene—other light types (not ambient) in the scene will affect only specific areas of the scene.

In the example scenes to the left and below we have ambient light in a room. Notice how the light is the same all around. We have walls of the room and in the room are a sphere and a cylinder. Light appears to come from all around.

The left example is from Vue Infinite 6 and the example to the right is nearly the same scene in trueSpace 7.51. The light colors and angles for viewing the two scenes are slightly different. Each of these products has a variety of controls for adjusting ambient lighting conditions. In photography ambient light is often used in contrast to directional light, which is specific and applied to objects often by the photographer. Ambient light in this sense may be unwanted light that fills the room and is out of the control of the photographer.

In 3D applications, since you control the ambient light, there can be so much ambient light that it washes out everything in your scene. If you have ever been at the “start of a rainbow” you find yourself bathed in orange light from all around. This light is ambient light and appears to come from everywhere. Typically in such light you will not see shadows from any of the objects in the area.

In a very dark scene ambient light can be used to add a sense of mystery to your work. A low level of ambient light can be used to provide some non-directional illumination over the entire scene and bring out details in a way where the low illumination shows objects in the scene but gives them a sense of suspense and uncertainty. Controlling ambient light in a scene is often just the use of sliders to enable or disable the light and its intensity. Get to know where to find those controls in your favorite software.

 

Global ambience
Global ambience is another term for ambience, but some software uses this term differently as a variation on the notion of ambient light. Typically a sky, which is normally a source for ambient light, will have colors in it, such as shades of blue running toward red shades. In global ambience for some software, those parts of the scene that are more exposed to the blue section of sky will appear with more blue and those sections of the scene that are more exposed to the red section of the sky will appear with more red.

 

Working with Point Lights and Local Lights

Another useful light called a Point Light or Local Light is a light source that is a single point, much like a naked light bulb hanging from the ceiling in an old basement. The light radiates from the point, and typically decreases in intensity the farther you are from the point. A couple of examples show this kind of light. We have used a Point Light in the Vue Infinite example (below, left) and a Local Light in the trueSpace example (below, right). In the Vue example the light is visible as an object in the scene. In order to get the same effect in the trueSpace example we have used a clear sphere placed over the light source to simulate an object emitting that light. The trueSpace example shows the scene with "Cast Shadows" turned off, and the Vue Infinite example shows the scene with Shadows. This is something that is not so easily done in the real world, is it? Normally in the real world you take the shadows you get especially when you are a photographer. (Photographers move around in the real world to get the best shot, or sometimes they find it useful to add light with a flash or a portable lighting device.)

Keep in mind that a point light does not have a direction associated with it, instead it radiates equally in all directions.

Falloff is a term used to describe what happens to the light as you move farther away from the source: the light decreases (or falls off). 3D applications let you control the falloff rate, unlike the real world. In the real world an inverse square relationship exists that governs falloff. It works like this: if you measure the amount of light (let’s assume you have a photographic light meter in your hand and it reads 100 lumens) at a certain distance from the light (we’ll say 5 feet), then move twice the distance away (10 feet), the light will only be one-fourth of the first value (25 lumens). This example is an illustration of the inverse square relationship in the real world. 3D lets you often control the falloff so that it can be zero, or something more than the real world values. You can do things in 3D that the physical world you live in just does not allow. A falloff of zero means that the light does not decrease in strength or power as you move away from it. Do you know any real world lights that behave like this? In fact, none do, but one appears to follow the principle of no falloff: the sun. In order to observe the inverse square relationship with the sun, you have to move really large distances away from it such as millions of miles.

With point lights you can change the color and the intensity. Many other effects are possible with lights, but we’ll save that discussion for when we get to talking about Spot Lights. That comes up next after a departure to talk about Light Gels.

Light Gels
Many of the techniques used in discussing lighting come from theater where they were first introduced. 3D programs have worked hard to simulate the physical effects possible in theater lighting. Take Light Gels for example. This term comes from the history to theater lighting where colored gelatin was used in a holder placed over a light to give it color (around 1919). The intense heat of stage lighting would dry out the gel over time and make it less useful. The drying might even be sufficient during a performance to cause the gel to change in color as a result of dehydration. (A curious footnote to all this is that theater lighting had become the subject of serious investigation by the early 1920s.) So, what 3D does with Light Gels has a long history.

In the digital world we do not need light gels for color. Usually a slider handles this quite well, or a color selector tool will make the color change. In 3D then why are “light gels” still used if all they do in theater is add color? The simple answer is that light gels are used for much more, also in theater. They can add patterns to the light that is emitted. In some applications you can put a light gel on Sunlight so that the sun’s output is not very uniform. Below are examples of pattern light gels, which are just image files that can be loaded into your 3D program and used with a light. Each of these patterns can be applied over a light causing its output to be more diffuse and varied. The white regions do not block light passing through, the gray regions block some, and the black areas block all light. When you use such light gels with sunlight, you can create sunlight this is broken up and appears to be passing through a cloud formation.

These types of light gels are very easy to create in software such as Adobe Photoshop or Artweaver (a free Photoshop look-alike product that can handle PSD formats and layers). The above examples are JPG files. Take a look at the Point Light scene on the left (made in Vue Infinite). Here is that same scene with each of these light gels applied to the point light.

The gels were applied to the point light using a spherical mapping. The effect is even more pronounced when the light intensity is increased. In the examples below we go from power 100 to 300.

In the examples below the gel can be used to create a nearly supernatural, alien world. The same scene is used with a different gel. These types of effects are not as easily achieved by creating objects with textures. The point light is projecting the pattern and the colors of the light gel into the room.

Keep in mind that you can make your own light gels if your 3D program allows importing of image files for textures. A program such as Artweaver or Photoshop can be used to create a JPG file or other type of image file. The image can be black and white or in color. Any image, such as a photograph that you took in your camera or a picture found on the web. The lighter parts of the image will allow the point light to pass through the gel, and the darker parts will block it. The amount of blocking depends on "how close to black" the color is. Try experimenting with this approach: create your own basic light gel and load it into your 3D software. Once you see how it behaves, try changing it but guessing the effect before you install the changed light gel. Try to think about how the light gel you plan to make will behave in the scene before you actually do the work. This will help you to learn the "Vocabulary of 3D" or how to think in 3D terms and effects.

Rendering Engines
As you can already see, the topic of light is extensive and really we have by no means scratched below the surface of the topic. 3D software differs from product to product in how light is handled. And for good reasons. When we simulate the real world, we can make choices. There is not one, fixed way of doing a particular approach. By working with the different products, you start to build up a “bag of tools” which can help you in different ways: expand your understanding so that you can better evaluate a new package coming down the pike, reach for the best method to handle a particular problem, select a specific effect that no other combination of tools will give you.

In the Lab with trueSpace 7.51 you can choose different rendering engines: VRay, LightWorks and Virtual_Light which are from 3rd party software companies. Each of these gives you features that are handy to have around, and depending on the situation you work in, you will find that you are able to bring in your selection from this group of tools to achieve a specific result.

Check out these web sites for information from the various developers:
    VRay: http://www.chaosgroup.com/
    Light Works: http://www.lightworkdesign.com/products/advrender.htm
    Virtual Light: http://www.3dvirtualight.com/

As your skills increase you will find that this is an excellent collection of tools to have around. We will come back to this topic in a later article.

Volumetric Lights
Volumetric Lights address another issue of simulating the real world. Take a look up in the sky toward the sun and you will not on almost any day there is haze or dust suspended in the air. This haze affects the way the light behaves, wrapping almost a smoky thin cloud around the light source. Another way of expressing this idea is to say that it appears that the light has a fog around it. This real world phenomenon is addressed in 3D software through the use of Volumetric Lights. As soon as you add a volumetric light to your scene, you see right away that the scene takes longer to render. The light type is more complex, since it must also take into account the interaction with the atmosphere. Rendering engines need to worry about such things. Doing test renders as you work in 3D is essential, but you can slow yourself down quite a bit if you need to work with volumetric lights. Try this method: switch the volumetric lights off or delete from the scene to do your basic design work. Add them back in or turn them on when you want to do a full test. In this way you will get good performance in your test renders and you will take into account the various light sources. Even with a very fast computer workstation, you will find as your project grows that no matter what the scene, rendering slows down with volumetric lights.

Casting Shadows
You will find that trueSpace 7.51 and Vue Infinite 6 both have features that enable you the change whether or not your light source casts a shadow. This can be handy. It may reduce the complexity of the scene or simply allow you to do something else with the space in a scene that would normally have a shadow, perhaps hiding something you wish to be seen. When you use lights, play with them, turning shadows on and off. Take note of the effects that you see. Render the scene both with shadows on and shadows off.

Some tools go beyond turning shadows off or on. They also let you control the density of the shadow. In Vue Infinite 6 you have this option to work with. Not all the lights in your scene need to have the same properties. Experiment with changing some of them and keeping others at the default settings.

Some 3D programs let you control how far the light reaches, and then cut off the light beyond that distance. This is another feature you will not find in the real world, but it may prove useful to you in your work.

We recommend that you build a working portfolio of you projects and their renders. Keep around the original project scene file as well as sample renders. Store these files in a safe place: copy to CD or DVD and keep multiple backup sets. As you do this you start to build up a useful collection for your work. From time to time, review your work, noting especially your render files. As you grow in 3D skills you will look at these renders in a different way. You will see aspects of your work that you missed. Part of becoming a successful 3D Profession is learning how to be a good critic of your own design work. Asking friends and family to review your work my get you lots of praise, but it takes a special eye to see the strengths and weaknesses of a render. Learn to build that eye for yourself. Being a strong critic of your work will help you the most as you move forward in this field.

 

Spotlights

Unlike the lighting types we have discussed so far, spotlights have direction associated with them. We can change the "cone of the light" by controlling both its spread and direction. These lights work very much like those that a professional photographer may bring with him to a shoot. A photographer will locate the light in the scene to give the best results, and he will aim the light so that it hits the objects in the scene that need the lighting. A photographer may also add filters or gels. Some spotlights have a lens on them when allows you to move the light source closer to the lens or farther away. In this manner you can also control the spread of the light (whether it is a very narrow beam or a wide beam). These features are implemented in 3D software as well, and each selection of program will give you different choices on how to make changes. By experimenting you will be able to get the effects that you need.

Below is an example of spotlight illuminating the scene from above with the cone and sphere.

Light Panels

Light panels are rectangles of light that you can scale and move around. You can change the intensity and color. The panel can be used to create a wall that is source of light in a room. Light panels are found in many real-world situations, such as fluorescent lighting fixtures in the ceiling. Skylights can be another example. Typically light panels in the real world are above us, but in the digital world you can change things around. We finish this section and this article by giving some examples of light panels. A suggestion is that you experiment with them in your work. Try using them in the conventional way as ceiling lights, but also try them elsewhere: lighted walls of staircases, floor lighting, lighting at the bottom of a fish pond.

 

 

Additional articles will appear in this section.

 

Topics for further exploration and reading on your own


1. What is ray tracing? How much do I need to know about ray tracing?
2. Where can I find discussions on the web about the issues covered in this article?
3. I'm very new to this field. Where can I find others who are new to the field and discuss with them?
4. I have a limited budget. What free tools are out there where I can learn these topics better on my own?
5. Learn the following terms: specular light , diffuse light, lens flare. Does your 3D application allow you to control or adjust these settings in a scene? Keep copies of renders with these settings enabled and disabled. A future article will discuss these topics with examples.
6. This article contains some web links. Visit those sites and explore those pages.
7. If you do not yet have a portfolio of 3D projects and renders, then it is time to start one. Try out each of the options mentioned here in your software. Keep examples of your work for future reference.
8. Change the positron of your camera as well. We talk here mostly about changing parameters for lighting, but also change the position of your camera. You will notice that your view of the scene will change, and you will uncover useful information about your project when you look at it from a different angle.
9. Practice in 3D software every day. This is the only way you will become an expert.
10. Tell a friend what you learned by reading this article. Show him or her some examples. You will increase your understanding of the topics presented here when you present them to someone else.
11. Revisit software web pages frequently. Products often change, new features are added, and ways of using the product to get a specific effect are described. This is a rapidly changing area. Opinions formed last week or last month may be out-of-date in a short time.

We enjoy hearing from you. Some of the questions listed above will appear in future "Topics in 3D" articles. Please send your comments about this article to