The Science & The Basics
I’m not sure many people fully appreciate the nature of what artists attempt to do each time we set out to render light and shadow in art. I know I haven’t fully understood it, let alone appreciated it, even as I am in the middle of rendering.
As I continue to really dig into what Light is, I am awestruck and so thankful to all the scientists and artists who came before me—the giants upon whose shoulders we stand—because the subject of Light is huge, and I am glad they already figured all this stuff out for us 😅.
It is difficult not to get philosophical here because what we are really doing when we render light is re-creating the properties and behaviors of light in a 2D space—and those behaviors and properties encompass several sub-branches of modern Physics, including: Quantum Physics, Modern Optics, Geometric Optics, and Physical Optics.
Let’s take a moment to appreciate the fact that different aspects of light behavior and properties come under several different categories of Physics that are each quite involved areas all their own.
That was my not-so-subtle warning that The Fundamentals of Light gets quite technical.
The understanding we gain for our art is totally worth it, and we need three things for sure: 1) Patience, 2) Plenty of visual examples, and 3) More than one post to go through the massive amounts of information.
For any of you who are much better scientists than I, please forgive any inaccuracies in my scientific understanding or explanation. I endeavor to be an expert artist, not physicist 😋 , but I do try to be as accurate and as clear as possible. If I get something wrong, please let me know in the comments and I will do my best to make corrections.
I hope you will hang in there with me as I break down the technical bits (that’s the patience part), I hope the examples and information I share help your practice, and that you’ll find it useful enough to look forward to the future posts in this series. Since this is the first, let’s start digging into to the science, shall we?
The Science—What is Light?
To understand how to render light and shadow we must grasp the concept of what light is and how it behaves.
Light is a type of energy created by the emission of photons within the electromagnetic spectrum. If that sounded like gobbledygook, fear not, I shall explain.
A photon is a “small bundle” of electromagnetic energy and the basic unit that makes up all light. Thus, photons are the building blocks of light.
Electromagnetic energy describes forms of energy that are reflected or emitted from objects as electrical and magnetic waves that can travel through space. The Electromagnetic Spectrum shown below describes these energies as frequencies and wavelengths.
The light effects we paint represent a fixed and narrow range of the Electromagnetic Spectrum called the Visible spectrum, which is a narrow group of wavelengths between approximately 380 nm (nanometers) and 730 nm.
As illustrated in the diagram above, The Electromagnetic Spectrum contains several other forms of light, however most of them are at frequencies we can feel but not “see”.
All light has both a frequency and a wavelength, and all light can behave as both a particle and a wave depending on the situation. In fact, both light and matter have particle-wave duality in their properties and behavior. It’s important for artists to understand this duality because it affects our thinking and problem solving regarding light at different stages during rendering.
When we begin to invent our images we must also invent our lighting. When we are mentally calculating the direction of our light source, its reflections, and fall off, it is helpful to think of light as particles, or rays, that travel in straight lines.
This helps us figure out how much of our object will be lit, how to place the form shadows and cast shadows, and where the bounce light will land. When objects are opaque, I have found considering light primarily as rays helps me best determine how to render the light.
When objects are translucent, transparent, or have variable reflectivity, things start to get more complex because light is not simply being absorbed and reflected but also transmitted through the object. Transmission of light through objects gives us more to consider and calculate because it gives us more to paint, like subsurface scattering, refraction, and more reflections.
Let me put your mind at ease and say it is not necessary to do any complex mathematic calculations to paint these effects, just some additional concepts to understand and visual calculations to make.
When we think about reflection, refraction, and absorption, it helps to think of light first as a particle or ray (for determining the light’s intensity, direction, and bounce) and then as a wave—for determining which wavelengths are reflected off, absorbed by, and/or transmitted through the object and the ground.
That was a huge mouthful, I know. I will be going over all of these more nuanced areas in other posts in this series.
Understanding the particle-wave duality of light begins to give us a clear view of how light’s behavior changes as it interacts with different materials. Watching the videos below helped me gain a clearer understanding of this concept, and I hope you find them useful, too.
As we bring together the elements we need to understand, we start to define the contours of The Fundamentals of Light so that we can start filling in details and particulars—and don’t worry, there will be photographic examples and demos so all of this becomes more clear.
Properties of Light & Matter for Artists
I know this has been a little science-heavy so far, and that’s intentional. It is how I make sense of complex topics, and I hope you find it helpful. Now that we’ve covered the basics of what light is, I’ll change things up a bit to keep everything digestible. I’ll cover a little science and do some explaining, and then use photographic examples or demos to clarify how the information helps in creating art.
Next, let’s dig into the properties of light, but first I want to give you a list of all the properties to keep in mind whenever it’s time to render light. This is a list according to me, and they’re based on my experience rendering light in both 2D (Photoshop) and 3D (Maya).
|Light Properties||Matter Properties|
|Number of Sources||Form/Shape|
|Type of Light(s)||Local Color|
|Size of Source(s)||Material Type|
|Distance from object/picture plane||Density|
|Angle/Height of Source(s)||Reflectivity|
Some of these are straightforward, so let’s talk about those briefly. The number of light sources is an important consideration because we need to know how much light information we’re working with. More light sources in a scene makes for a brighter image, but how each source affects the picture plane depends on all the other properties on the list.
The size and angle/height of each source are also straightforward properties and they ask questions like: Is a light source large, small, or medium? Do several small lights make up one larger source because of how closely grouped they are? Do these sources sit high or low on the picture plane? Are they even visible in the image, or are they shining from somewhere out of frame?
Under properties of matter, shape, form, local color, and material type are the most straightforward. We must know what shapes and forms make up the volume of the objects we’re rendering, and we need to know what color and material type they are. After all, there is quite a difference between painting a shiny chrome ball and painting a shiny colored plastic ball. Sure, they’re both shiny; but one is metal and ridiculously reflective while the other is plastic, softer, and much less reflective.
The Two Ways Our World is Lit
Despite all the science, properties, and moving parts involved with understanding how objects are lit, there really are only two ways anything receives light in our world: directly or indirectly.
Objects are either lit directly by a light source or indirectly by reflected light when the rays from the source bounce off some surfaces and objects to illuminate others. This kind of indirect lighting is also called Ambient Light and it is much weaker in comparison to direct light. Most lighting schemes will involve both direct and indirect lighting.
Next, we’ll go over the categories that light sources fall into.
Properties of Light – Types of Light Sources
There are 3 types of light sources:
- Key Light
- Fill Light
- Rim Light
A key light is the strongest light source in your scene. It defines the emotional impact of the scene and is the primary descriptor of forms and drama. When you decide how to “key” your scene, you are choosing the overall mood and tonal range that will define it.
A fill light is not as bright as a key light and is often softer and a lot darker. Fill lights support your scene and subjects by adding light and color information in the shadows, which can illuminate an area of interest you wish the viewer to see or just provide added interest or balance to your scene. Fill light can be ambient (reflected) light, as I’ve done in my examples below, or it can come from an additional light source(s).
A rim light travels the outer edges of objects. Rim light helps define shapes, add dramatic appeal, and can be a helpful tool for adding compositional information and/or emotional impact.
No matter what kind of mood a story or scene calls for, any lighting scheme will have at least a key light and, likely, some combination of all three light source types.
Okie dokie, how’re you doing? I know this has been a lot to get through, and I hope you’re still hanging in there with me. Deep breaths, we’ve got this!
Now, it’s time to go over some terminology to help keep things clear as we continue to move through the Fundamentals of Light.
Defining Terminology + Sphere Tests
Think of this as the glossary section of this post. Here I’ll define the frequently used terms that will show up quite often from now on in both my writing and the call-outs in demos and examples.
Anything that creates and emits light. Light sources can be natural, like the sun, moon, and fire, or artificial, like lamp posts, flashlights, and device screens.
Light Direction & Angle
The orientation of a light source relative to the picture plane. For example, low and out of frame on the left, or mid-level and in frame on the right.
The intensity or strength of a light source. A high exposure light source makes for a brighter, “high key” scene, while a lower exposure light will make a scene appear less bright. I tend to use exposure and intensity interchangeably.
The area of a form receiving most of the light; the lit side of a form.
The brightest area on a form. This is usually a small area that is receiving the most direct light and reflecting a bit of it back.
The area on a form that has begun to turn away from the light source, resulting in a transition area of light to shadow. This area is receiving some light, but not nearly as much as the parts of the form facing the light source more directly.
Light that bounces off a surface and then lands on another form or surface is Reflected or “bounce” light. Reflected light is much weaker than direct light and can occur on any part of a form, except occluded areas.
The point at which light cannot land on a surface. This is where the shadow side of the form begins.
The darkest part of the form shadow. The shadow core on a sphere typically looks like a dark band right next to the terminus, a clear separator between the light and shadow. The core shadow is also the part of the form shadow least affected by reflected light.
The areas of a form that are in complete shadow and receive no direct light.
Occlusion shadows are the darkest areas in shadows and on/within forms where absolutely no light can reach. When something is occluded it is completely obstructed or blocked, so when light is occluded you have complete darkness.
We see occlusion most often in narrow areas right beneath forms before the cast shadow begins, and with narrow openings, cracks, and crevices of surfaces/forms. Occluded areas are not sufficiently open enough to the environment to receive any light, so there is only shadow.
Cast shadows is created when an object’s form blocks light. Objects block light adjacent to themselves and in the shape of their contours. There are three distinct parts to a cast shadow, the Umbra, Penumbra, and Antumbra. Much of the time, in art, we are only painting an umbra and penumbra. When multiple light sources of different intensity and direction/angle are involved, we begin to see examples of all three parts of a cast shadow.
- Umbra: Umbra is Latin for “shadow”. The umbra is the innermost and darkest part of a cast shadow, where the light source is completely blocked by the form creating the shadow. [i]
- Penumbra: Penumbra is Latin for “nearly” and “almost”. The penumbra is further from the object and lighter than the umbra. Further away from the object light from the source and the environment can influence and brighten the shadows.
- Antumbra: The antumbra is the lightest and softest part of a cast shadow. The technical definition is confusing and unnecessary for our purposes, but if you’re curious click here.
Now, I’m going to show a few sphere test examples to visually illustrate the terms above so we can make practical sense of all you’ve been reading.
The Distance of Light Sources & Why It Matters
Each property of light plays a role in affecting the mood of our scene and the light effects we paint, including shadows. The appearance and quality of shadows is determined by the light and forms that cast them. How near or distant a light source is to an object has a significant impact on the appearance of an object’s form shadows and cast shadows, so let’s get into that next.
Distant Light Sources (Sunlight, moonlight, spotlights, etc)
We can group lights into categories based on their characteristics, like size, distance, and how intense they are to get a starting place for how those lights would interact with the objects in our scenes.
Distant light sources are things like sunlight, moonlight, and powerful spotlights like those in stadiums and theaters. Distant lights tend to:
- Be neutral lights.
- Cause soft-edged form shadows.
- Create cast shadows that are the same size and shape as the object because their light rays are parallel.
As one example, we know the sun is a huge, very distant, powerful light source, and from observation we know that light from the sun strongly illuminates everything it reaches. That means light is bouncing around everywhere in our atmosphere and reflecting a lot of light, so we can expect brighter and more colorful shadows when the sun is involved.
Playing with exposure also makes a big difference, so an overcast grey sky lowers the exposure, diffuses the light, and makes the sunlight seem much less energetic than a clear and cloudless sky, and creates lighter, softer, and less colorful shadows.
The Sun is also larger than our Earth, and any object we would light with it, so we must also consider the sun as an “oversized” light, which we’ll get into in a minute.
Nearby Light Sources
Nearby light sources are things like lamps, candles, device screens and monitors, lighters, matches, lanterns, etc. Nearby light sources tend to create:
- Larger cast shadows because the light rays are no longer parallel.
- Shorter and sharper (harder edged) cast shadows the closer they are to objects, longer and softer cast shadows the further they are from objects.
- A higher terminus and a larger form shadow.
- A more active or energetic feel and added tension to a scene.
When nearby light sources are also quite small (like candlelight or a lighter), they tend to cast hard edged cast shadows. They present an additional composition challenge because they can become distracting if not handled carefully. Nearby light sources tend to become a focal point in a scene, so it’s important to be mindful of that and use it to your advantage for your chosen lighting scheme and compositional design.
Oversized or Diffuse Light Sources
Examples of oversized or diffuse light sources are the entire sky on an overcast day (sky light), light coming through large windows, and any light that is scattered by being translucently covered or blocked (like a paper lantern, a light sheet or cloth, an umbrella, or frosted glass covering for light bulbs). Oversize or diffuse light sources tend to:
- Cause an object’s terminus to move further away from the light source (the larger the light source is larger relative to the object).
- Create softer edged shadows.
- Make environments and characters feel softer, warmer, and more friendly.
In the case of light sources that are larger than the objects they illuminate, the light rays are travelling out in random directions, reflecting off the atmosphere and other objects and surfaces, and filling in the shadows, which softens them. Shadows become softer edged because light does not reach each part of the shadow area equally, and because the object blocks (occludes) part of the light area behind it.
Ambient light is created when light from a source is reflected off the ground, other objects, and the environment. It is possible for objects to be exclusively lit by ambient light, but a key light (which is usually a direct kind of light) is still needed to emit the light that will be reflected.
Terms like indirect light, reflected light, and bounce light all mean the same thing: they are all ambient light. Ambient light is most noticeable in shadows because of the contrast, but it is present whenever and wherever reflected light lands on an object or surface.
Light rays lose most of their strength and brightness (90%) with each bounce, and they are bouncing around multiple times. This loss of strength is why ambient light is generally weak and cannot reach into occluded areas.
You may have come across the term ambient occlusion, especially as it relates to lighting in 3D modeling apps like Maya and Zbrush. In drawing and painting, if zero light can reach an area, I simply refer to this as an occlusion shadow or an occluded area.
For a bit more on ambient light and ambient occlusion, here’s a video by Marco Bucci (awesome artist!) that I found helpful.
Light Direction & Angle: How They Affect A Scene
In any lighting scheme, cast shadows are a compositional and mood element that should be considered and planned. Choosing the light’s direction and angle is an important step in setting the emotional tone of a scene as well as defining forms and helping viewers to understand how to react to what they are seeing. Cast shadows can add drama and mystery to a scene, particularly when the object or character casting the shadow is off camera.
Different light directions and angles offer a variety of mood options, and I’ve listed a few here:
- Direct Overhead Lights:
- Tend to read as unnatural.
- Can help create tension and drama, and how much depends on the light’s exposure and temperature.
- Angled Light from the side:
- Defines form.
- Reads as active and energetic.
- Adds dramatic tension.
- Frontal light (slightly to the side and above, not directly in front):
- Comfortable way of positioning light.
- Keeps an object/character from being in too much shadow.
- Good at defining form.
- Reads as soft and friendly.
- Under Lighting:
- Is the most unnatural of all the lighting directions.
- Feels dramatic in spooky, creepy, threatening, and unnatural ways.
How you choose to render your light will always depend on the position and point of view of the audience, and the message that needs to be conveyed.
The Fundamentals of Light—Breaking Down The Parts
Even though we learn in steps and stages, I find it helpful to get the “lay of the land” because it provides a road map, and it’s nice to at least have some idea of what we’re doing, right? With that in mind, I have listed the major headings that are part of studying The Fundamentals of Light and broken out some detail for the area we’ve covered today.
- Properties of Light
- Light Sources
- Types of Light
- Terminology & Sphere Tests
- Fall Off & Form Changes
- Light & Surface Color
- Translucence & Transparency (Transmission)
- Light & Materials
- Atmospheric Effects & Atmospheric Perspective
- The Human Experience of Light
- Rendering/Visual Styles
Next Time: The Fundamentals of Light, Part 2!
Take a moment to think of your absolute favorite treat for relaxing and pampering yourself. See it, visualize it in your mind’s eye. Now…get yourself that treat! You have just made it through a massive amount of information in a relatively short(ish) amount of time.
Thank you for hanging in there with me. I’ve tried to keep things clear and concise, but I know this was a lot to take in. I commend you, I thank you, and I am sending you virtual high fives and fist bumps!
The next couple of posts in my Fundamentals of Light series will cover exposure and fall off, and then absorption, reflection, and refraction of light wavelengths.
If I’ve confused you, if you have questions, or if I’ve gotten anything wrong, please message me in the comments and I’ll do my best to clear things up.
I hope you’ll join me for those as well.
Take care, and happy drawing everyone!