Lighting & Materials

A point light is located at a point in space and sends light out in all directions equally. Examples include lamps or other local sources of lights. The intensity of such light diminishes with distance, meaning the closer an object to the light source, the brighter it is.^[1]

Like a point light, a spotlight has a location and a range. However, it's constrained to an angle, producing a cone-shaped region of illumination — like in flashlights, car headlights, and searchlights. Light also diminishes at the edges of the spotlight's cone.

The best way to recreate sunlight or moonlight in 3D is to use directional lights — think of them as distant light sources that exist infinitely far away. The light object can be placed anywhere in a scene as it doesn't have any identifiable source position. Also, because the distance of the light from the target object is not defined, the light doesn't diminish.

Where there's light, there are shadows. If you looked out from a light source, all of the seen objects appear in light, and anything behind those objects is in shadow. There are different types of shadows you can use in 3D. Hard shadows indicate light from a small point source, and they have crisply defined sharp edges.

Soft shadows look realistic as they are less distinct and fade off toward the edges. Soft shadows come from larger light sources. To achieve a higher degree of realism, it's best to use soft shadows together with other types of softer or less direct light in a scene.^[2]

Most objects don't emit light — they are illuminated by light sources, and we see them as a result of the light reflected off them. As you probably know, light moves in straight lines, so when we emulate a light source in 3D software, the parts of the object that aren't hit directly by the light remain dark. This is how direct illumination or direct lighting works.

In the real world, after hitting an object, the light bounces countless times in the environment. It's called indirect illumination or indirect lighting, and it's the reason why objects are rarely completely dark, even when they are out of direct light. One of the algorithms to create convincing ambient lighting in 3D is called global illumination — it calculates light traveling throughout the entire scene, taking into account both direct and indirect illumination.

In real life, material is what the thing is made of. In 3D graphics, materials control how a 3D object appears on the screen and interacts with light. They define the basic optical properties of objects like shading, specularity, reflectivity, color, transparency, etc.^[3]

Most materials take texture as a parameter. A texture is an image used to skin 3D objects. It breaks up the uniform appearance of the material, as very few objects in the real world have completely uniform surfaces. It also gives you control over object properties on a finer level. Artists usually start by finding or creating textures that match the surface of the object they want, then they add material and apply the textures.

Reflectivity is an optical property of material, which describes how much light is reflected from a material compared to how much light strikes a surface. Different materials have different reflectivity. The light reflected off a smooth surface produces a direct reflection, also called specular. On a rough surface, the reflection is diffused or scattered.^[4]

To understand what specular reflection is, let's quickly go over some basic terms. The ray of light that strikes a surface is called an incident ray, and the angle between this ray and the perpendicular or normal to a surface is the angle of incidence. The reflected ray is the ray reflected by the surface, and the angle between the surface normal and the reflected ray is called the angle of reflection. When the angle of reflection equals the angle of incidence, we have a specular reflection. Think of mirrors or still lake water.

If you put a straw in a glass of water, you can see it bending where it enters the water. This illusion happens because of refraction — the change of direction of light rays transmitted through the surface.^[5] This transmitted ray of light is called the refracted ray, and the angle between this ray and the normal is the angle of refraction.

Different transparent materials have different refractive indices, also called indices of refraction, that determine how much the path of light is bent when entering a material. A change in speed causes the change in light direction — light slows down when it moves from air to glass and speeds up when it moves from water to air.

Depending on the amount of light that can pass through them, objects have different transparency — they can be considered transparent, translucent, or opaque.

• Transparent objects like eyeglasses or water look clear, and as light passes through them, you can see they cast a barely visible shadow.
• Translucent objects like most paper let some light through, and their shadows are slightly darker.
• Opaque objects like our bodies don't let the light pass through them, and they have very dark shadows.

When we look at distant objects outdoors, they often appear foggy or hazy. It can happen because as light moves through that air, it hits things like water vapor, dust, pollution, other gasses, which causes it to bounce off in a different direction and obscures the image. To simulate this effect in 3D, we can overlay a color onto objects depending on the distance from the camera.

Another option to create fog is by using volumetric fog. It provides a different fog effect and can be used to create puffy, cloudy fog or clouds that appear to drift and break up in the wind, as the fog density is not constant through 3D space. You can create volumetric objects from scratch or download them from open-source databases.