# 3.5 - Material Properties¶

A 3D model captures the form of an object, but we also want to model the surface properties of an object. Surface properties include, but are not limited to:

• What color is the surface? Is the color solid or multi-colored?
• How does the surface reflect light? Is it shinny or dull?
• Is the surface smooth, rough or bumpy?
• Is the surface flat or curved?
• Is the surface transparent which allows some light to pass through it? If so, does the light refract (change its direction of travel)?

All of these surface properties are fundamentally a question of how light reflects off of a surface into your eye (or the lens of a camera). If there is no light in a scene, you can’t see anything! And the characteristics of light are not uniform. For example, a disco might have a red strobe light, whereas a kitchen might have bright canister light over the stove. These two different light sources will interact with the surface properties of objects in very different ways. So we need to model light sources as well!

In fact, what we need to model is the interaction between the surface properties of an object and the properties of the light sources. This is complicated by the fact that real world scenes almost always have multiple light sources. A model’s appearance is a combination of reflected light both from the light sources and from light that has reflect off of other objects. This is such a hard problem that we typically just try to approximate what happens using simplified assumptions.

These tutorials will introduce the basic assumptions we use to model surface and light interaction. We will cover color issues and light reflection issues.

## Glossary¶

material properties
A mathematical description of a surface that determines how it is rendered.
light properties
A mathematical description of the light coming off a light source.
Next Section - 3.6 - Color