Arrow Group Industries LM86 Manual do Utilizador descarregar pdf (Página 53)

Maxwell Render 2.5 User Manual

Chapter 10. Maxwell Materials | 53

A surface which scatters almost all light in a chaotic, diffuse way is called a “lambertian”

surface, such as the red ball on the left. Lambertian reectance means that light falling

on a surface is scattered in such a way that the apparent brightness of the surface is the

same, regardless of the observer’s angle of view. Or else: the surface’s luminance is the

same regardless of angle of view. Many rough surfaces, such as unnished wood, exhibit

lambertian reectance.

A surface which scatters almost all light in a chaotic, diffuse way is called a “lambertian”

surface, such as the red ball below (F. 01). Lambertian reectance means that light falling

on a surface is scattered in such a way that the apparent brightness of the surface is the

same, regardless of the observer’s angle of view. Or else: the surface’s luminance is the

same regardless of angle of view. Many rough surfaces, such as unnished wood, exhibit

lambertian reectance

F.01 F.02

A smooth surface however reects light uniformly and creates a very sharp or specular

reection of its environment. Specular reection is the perfect, mirror-like reection of

light from a surface, in which light from a single incoming direction is reected into a single

outgoing reection, as for example with a mirror.

It is important to note that because very smooth surfaces reect light perfectly, they

reect much less of their own color. This is visible in the render (See above F.02), where

the ball is still tinted red, but as it is a tinted mirror, its own color shows much less. There

are a few exceptions however and one of them is metals. Even if a metal is very smooth,

it still reects its own color much more.

Transparency

An object becomes transparent when light does not stop at the surface, but goes through

the object and out the other side. When light passes through a material, it slows down

because the material is denser than vacuum. Because of this change in speed, the light

is bent, or refracted, when going from vacuum (or air) into the material. This refraction

occurs whenever light changes speed, so it happens when it moves from one material to

another with different densities. The refraction is also what causes “caustics”: concentrated

pools of light.

In the render below (F.03), it is refraction that makes the magnifying glass distortion,

and creates the caustics pattern. Different materials make light slow down more or less,

relative to the speed of light in air or vacuum. This difference between lightspeed in

vacuum <–> lightspeed in medium, is specied as the index of refraction (IOR, also called

Nd) for that particular medium.

F.03

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Arrow Group Industries LM86 Manual do Utilizador Página 53