Improve Your Artwork by Learning to See Light and Shadow ~ KrobKnea

by Monika Zagrobelna

It's very common for painting tutorials to treat light as an addition to the picture, an atmosphere-maker. We can easily get the impression that the object has a universal form, and then with proper lighting we can change the mood of the picture. The truth is without light there would be nothing to paint! Until you realize that, you're shooting blind.
In the first tutorial of this short series, I'll introduce you to the art of seeing light, shadows, reflections and edges.

How Can We See?

As an artist, have you ever tried to answer this question? If not, that's a big mistake. Everything you draw is a representation of seeing, just like the laws of physics are a representation of real processes. There's even more to it—what we draw is not reality, or an objective image of reality. It's an image created by your brain, an interpretation of signals caught by your eyes. Therefore, the world as we see it is only an interpretation of reality, one of many—and not the truest or most perfect of them all. Only good enough for our species to survive.
Why am I talking about this in a painting tutorial? Painting itself is an art of darkening, lightening and coloring certain parts of paper (or screen) to create an illusion of looking at something real. In other words, an artist tries to recreate an image that could be created by our brain (it makes it easy for us, since we think in patterns—we tend to look for familiar shapes in abstract pictures).
If a picture is similar to what we see in our minds, we say it's realistic. It may be realistic despite not having any recognizable shapes or outlines—all you need are a few patches of color, light and shadow to bring something familiar to mind. Here's a good example of this effect:

To create a convincing picture similar to one created by the brain, first you need to know how the brain does it. When reading this article you'll find most of the processes quite obvious, but you may be surprised at how closely science can relate to painting. We tend to see optics as a part of physics, and painting as a part of metaphysical art, but that's a mistake—art is a reflection of reality seen through our eyes. In order to imitate reality, first you need to know what our minds find real.

So What Is Seeing?

Let's go back to the fundamentals of optics. A light ray hits an object and bounces to your eye. Then the signal is processed by your brain and the image is created. That's pretty well-known, right? But do you realize all the consequences that stem from that process?

Here comes the first, the most important rule of painting: light is the only thing we can see. It's not an object, not a color, not a perspective, not a shape. We can see only light rays, reflected from a surface, disturbed by the properties of the surface and our eyes. The final image in our head, one frame of the never-ending video, is a set of all the rays hitting our retina at that one moment. This image can be disturbed by differences between the properties of every ray—every one of them comes from a different direction, distance, and they may have hit a lot of objects before hitting your eye last.
That's exactly what we're doing when painting—we imitate rays hitting different surfaces (color, consistency, gloss), the distance between them (the amount of diffuse color, contrast, edges, perspective), and most certainly we don't draw things that don't reflect or emit anything to our eyes. If you "add light" after the picture is almost done, you're doing it wrong—everything on your painting is light.

What is Shadow?

To put it simply, shadow is an area untouched by direct light. When you're staying in shadow, you're not able to see the source of light. That's obvious, right?

The length of shadow can be easily calculated by drawing the rays:

Drawing shadows may be a little tricky though. Let's take a look at this situation. We've got an object and a big light source. Intuitively, this is how we draw the shadow:

But wait, this shadow is actually cast just by a single point on the light source! What if we choose some other point?

As we can see, only point light creates a sharp, easily defined shadow. When the light source is bigger (more scattered), the shadow gains a blurry, gradient edge.

The phenomenon I've just explained is responsible for supposedly multiple shadows coming from a single light source too. This kind of shadow is more natural—that's why pictures taken with flash look so sharp and odd.

Ok, but that was just a hypothetical example. Let's take a look at this process in practice. Here's my tablet pen stand, photographed on a sunny day. Can you see the weird double shadow? Let's take a closer look.

So, light comes from the left lower corner, roughly. The problem is it's not a point light, so we don't have the nice, sharp shadow that's the easiest and most intuitive to draw. Drawing rays like this doesn't help at all!

Let's try something different. According to what we've just learnt, a big, scattered light source is made of many point light sources. When we draw it like this, it makes much more sense:

To explain it more clearly, let's obscure some of the rays. See? If not for these scattered rays, we'd have a pretty normal shadow!

No Seeing Without Light

But wait, if light doesn't touch the area, how can we see something that is in shadow? How can we see anything on a cloudy day, when everything is in the shadow of the clouds? That's the result of diffused light. We'll talk more about diffused light throughout this tutorial.
Painting tutorials usually treat direct light and reflected light as something totally different. They may tell you there's a direct light that makes surfaces bright, and that reflected light may occur, giving a bit of light to the shadow area. You might have seen diagrams similar to the one below:

This isn't completely true, though. Basically everything you see is reflected light. If you see something, it's mostly because light has reflected from it. You can see direct light only if you're looking directly at the light source. So the diagram should look more like this:

But to make it even more correct, we need to bring in a few definitions. A light ray hitting a surface may behave in a few ways, depending on the kind of surface it is.

When a ray is reflected fully by the surface at the same angle, it's called a specular reflection.
If some of the light penetrates the surface, it may be reflected by its micro-structure, creating a disturbed angle resulting in a fuzzy image. This is called diffuse reflection.
Some of the light may be absorbed by the object.
If an absorbed ray manages to get out, it's called transmitted light.

For now, let's focus on the diffuse and specular reflection only, since they are very important to painting.
If a surface is polished and has a proper, light-blocking micro-structure, a ray hitting it will be reflected at the same angle. Specular reflection creates a mirror effect—not only direct light is reflected perfectly, the same happens to the "indirect" rays (moving from the light source, bouncing off an object, and hitting a surface surface). An almost perfect surface for full specular reflection is, of course, a mirror, but some other materials give a good effect too (metal and water are examples of this).
While specular reflection creates a perfect image of the reflected object thanks to the correct angle, diffuse reflection is far more interesting. It's responsible for color (we're going to talk about this in more details in the next part of this series) and it lights up the object in a softer way. So, basically, it makes an object visible without burning your eyes out.
Materials have various factors of reflection. Most of them will diffuse (and absorb) a huge part of the light, reflecting only a small part as specular. As you probably already guessed, glossy surfaces have a higher factor of specular reflection than matte ones. If we look at the previous illustration once again, we can create a more correct diagram for it:

When looking at that image, you may be under the impression that there's only one point on a glossy surface where specular reflection occurs. That's not completely true. It occurs wherever light hits the surface, but there's only one specular ray hitting your eyes at a time.
Here's a simple experiment you can do. Create a light source (use your phone, or a lamp) and place it so that it lights up a shiny surface from above and creates a reflection. It doesn't need to be a very strong or vivid reflection, just make sure you can see it. Now take a step back, looking at the reflection the whole time. Can you see how it moved? The closer to the light source you are, the more acute the angle. Seeing the reflection directly under the light source is impossible, unless you are the light source.

What does this have to do with painting? Well, here comes rule number two. The position of the observer influences the shading. The light source can be fixed, the object may be fixed, but every observer will see it a bit differently. It's obvious when we think about perspective, but we rarely think of lighting this way. In all honesty— do you ever think about the observer when setting the lighting?
As a curiosity: have you ever wondered why we tend to paint a white grid on a glossy object? Now you should be able to answer this question yourself. Also, now you know how glitter works!

Value Is the Amount of Seeing

Value is the amount of information brought with light. We're not talking about color yet—for now, our rays can be only darker or lighter. 0% value (brightness) is no information. It doesn't mean the object is black—we just don't know anything about it and perceive it as black. 100% value is the maximum amount of information we can get at a time. Some objects reflect a lot of information to us and they appear bright to us, while others absorb a big part of the light hitting them and don't reflect too much—those seem dark. And what do objects look like without light? Hint: they don't.

This interpretation will help us understand contrast. Contrast is defined as a difference between points—the bigger the distance between them on a value scale, the stronger the contrast. All right, but where do different values come from?

Colors of Gray: Contrast

Take a look at the illustration below. The observer gets x of information from A, and y from B. As you can see, x is much longer than y (x=3y). The bigger the distance, the bigger information loss, so in the first situation we can see B as correctly illuminated, while A is a bit duller.
The other situation is different. Here x and y look roughly the same (x=1.3y), so they're going to bring a similar (small) amount of information.

The result from the observer's view would look like this:

But wait, why are the closer objects dark and the distant ones light? The lighter, the more information, right? And we've just said the information is being lost as the distance grows.
We need to explain that loss. Why can the light from very, very distant stars come to your eyes without larger disruptions, but buildings a few miles away lose details and contrast? It's all about atmosphere. You see a thinner layer of air when looking up than when looking ahead, and the air is full of particles. The rays traveling to your eyes at a big distance hit these particles and lose a bit of information. At the same time, these particles may reflect something else to your eyes - mainly blue of the sky. In the end, you'll see a leftovers of the original signal mixed with impurities - it looks bright, but it brings little original information and a lot of noise.

Let's come back to our illustration. If we draw the loss of information with gradient, it nicely shows why close objects are allowed to look dark. Also, it explains the visible value difference between close objects, and similarity of value of distant objects. Now it's obvious why objects lose contrast with distance!

There's even more to it. Our brain perceives depth by calculating the difference between images seen by each eye, and with distance this difference becomes less and less significant. In the end, distant objects seem flat, and close ones are more 3D.

Edges (lines) are a side effect of a proper lighting on the picture. If your painting looks flat and you need to draw outlines to bring attention to the shapes, you're doing it wrong. Lines should appear on their own as borders between two different values, so they're based fully on contrast.

If you use the same value for two objects, you'll make them look merged.

The Art of Shading

After all this theoretical stuff you should have pretty good knowledge on what's actually happening when you paint. Let's talk about practice now.

3D Illusion

The biggest issue with shading is that it's about creating a 3D effect on a flat sheet of paper. However, it's no different from drawing in 3D! An artist can go pretty far avoiding this problem, focusing on a fully cartoon style, but eventually if they want to progress, they'll need to face their arch-enemy: perspective.
What does perspective have to do with shading? More than one could think. Perspective is a tool to draw 3D objects in 2D without making them look flat. Since they're 3D, light strikes them in various ways, creating highlights and shadows.
Let's try a little experiment. Try to shade the object below using the given light source:

It'll look something like this:

It looks pretty flat, doesn't it? More like a simple gradient put on a 2D surface.
Now try to shade this one:

Here's what your drawing should look like now:

Now that's a different story! The object looks 3D despite the simple, flat shades we've added. How does that work? The first object has one wall visible, so for the observer it is actually one flat wall, and nothing else. The other object has three walls, and we know 2D objects don't ever have three walls. The sketch itself looked 3D to us, so it was very easy to picture the parts that light can or can't touch.

So next time you prepare a sketch for your painting, don't draw it as lineart. We don't need lines, we need 3D shapes! Build your objects using figures in perspective—make the shapes show. If you define the shapes properly, not only will your object look 3D, but you'll find shading is suddenly surprisingly easy.

Once the basic, flat shading is done, you can refine it, but don't add any details before that point! Basic shading defines lighting and lets you keep everything consistent.

Terminology

Let's take a look at the correct terminology when discussing light and shadow.

Full light is the area in front of light source.
Highlight is a place where the specular reflection finds its way to your eyes. It is the brightest point of the shape.
Half light is a full light darkening gradually toward the terminator.
Terminator is a virtual line between light and shadow. It can be sharp and clear or soft and blurry.
Core shadow is the area that faces away from the light source and is therefore not illuminated by it.
Reflected light is diffuse reflection hitting the core shadow. It is never brighter than the full light.
Cast shadow is the area blocked from the light source by the object.

Although it may seem obvious, the main lesson you need to take from this is: the stronger the light, the sharper the terminator. Therefore, a sharp terminator is an indicator of some kind of artificial light source. To avoid it, always blur the area between light and shadow.

Three-point Lighting

Once you've realized what seeing really is, photography doesn't seem so different from painting. Photographers know that it's light that makes a picture, and they can use it to change what they want to show. It's said that nowadays photos are too "photoshopped", but the truth is a photographer rarely takes a picture of something as-is. They know how light works and they use it to create a more attractive picture, and that's mainly why an expensive camera doesn't automatically make one a professional photographer.
You can take two different approaches when setting lighting for your picture:

Imitate nature, creating the light as it usually occurs.
"Sculpt with light", creating a conducive light to show something as attractively as possible.

The first approach will help you create a realistic effect, while the other one is a way to enhance nature. It's like a warrior in old, dented armor with a club in hand versus a beautiful elf-girl in shiny, impractical armor, wielding a magic weapon. It's easy to say which is real, but which is more attractive and eye-catching? The decision is for you to take, but remember to always take it before painting, not during, or only because something went wrong.
To clarify, it's about style of lighting, not about subject. You can use realistic lighting for a unicorn or a dragon, and you can as well ennoble the weary warrior. Sculpting with light is about putting the light sources exactly where they should be to emphasize the outlines of muscles or the shine of the armor. In nature it rarely works this way, and usually all objects of the scene look like a whole. Therefore, I'd suggest the natural method for landscapes and the enhancing method for characters, but by mixing both methods you can create even better effects.
Realistic shading can be learned from nature only. Don't use pictures of others or even photographs, because they can use "cheating" you won't even notice. Just look around, keeping in mind all you see is light. Locate the specular and diffuse reflection, observe shadows and create your own rules for it. However, you need to keep in mind that people pay more attention to the details of a photo or painting than they do to the general world around them. Images are easier to "absorb", since they engage only one sense, and can be focused on. The consequence is your pictures are going to be compared to other still images, not to reality.
If you choose the other approach, there's a trick I can show you. Photographers call it three-point lighting, although you can also use a two-point method for a more natural effect.
Let's start with a simple object. This teddy bear has been put in a space with a distant, weak light.

Let's put a strong light source pointed directly at the bear's front side. Use it to add in primary lights and shadows, then blend the shades. This strong, direct light source is known as a key light.

To drag the teddy bear out of the darkness, let's put it on an infinite ground. The ground is affected by the light source and a cast shadow appears. Since rays hitting the ground are diffuse, they are reflected at the teddy bear too. There's also a thin layer of blackness under the bear—it's called crevice shadow and it occurs every time the object isn't merged into the ground.

Let's put our teddy bear in the corner of a room. This time, light rays hit the walls too and we've got a lot of diffuse reflection everywhere. Therefore, the darkest areas of the teddy bear get a bit of illumination (not as bright as from the direct light, though) and the contrast is balanced.

What if we remove the walls and add some thick atmosphere instead? Light is going to be scattered, and we'll still have a lot of diffuse reflection. Soft light or diffuse reflection coming from the left or right of the key light is called fill light and is used to fill shadows which are too dark. If you stop here, you've created two-point lighting, which often occurs in nature, where the sun acts as a key light and diffuse reflection from the sky creates the fill light.

We can add the third "point" to it, the rim light. It's a back light, usually placed so that the object blocks most of the light from reaching the viewer's eyes. Rays avoiding the object create a clear edge, distinguishing the object from its background.

Rim light doesn't necessarily need to create a thin "rim". Its function is just to make a rim pop out, so you can use any direction and sharpness you need.

One more tip: even if you're not drawing a background, paint the object as if it had some environment. When painting digitally, you can even create a kind of background-dummy on a different layer, with messy patches of light and shadow that will help you calculate what should affect the object.

Conclusion

Light forms everything we see. It constantly hits our eyes, bringing information about the environment. It's the primary source of every image, and should be considered as the only thing we can paint. If you want to paint realistically, forget about lines, about well-known shapes—see them as something invisible, swamped with light. Stop separating art and science—without optics we would see nothing, and we would paint nothing. For now it may look just like a bunch of theory, but look around and you'll realize it's everywhere. Start using it!
This article was focused on value, but that's only a part of amazing things light does to our eyes. Stay tuned for the second part, all about color in painting!

KrobKnea