Amaan Akram--November 1999

Note: This tutorial was written for Lightwave 5.5, but can be applied to any 3D software.

Contents

1.      Preface

2.      Introduction

3.      Some Characteristics of Light

• Color
• Reflection & Refraction
• Intensity Falloff

4.      Observing Light

• Natural Light

5.      The Lightwave Lighting Engine

6.      Some tips on Lighting.

7.      Application

Preface

Lighting in Lightwave is a tutorial designed for application of lighting theory to computer graphics and requires a basic understanding of 3D principles. I will predominantly concentrate on natural lighting, but will mention a few things about artificial lighting as well. The overall thrust of my article will be to produce photo-realistic images by applying good lighting techniques and post-processing. In the first part of this article will explore the theory, and in the second part, I will take you through a step-by-step tutorial to produce a simple 3D scene lit by simulated sunlight. I will try to make the application part of this article as much software independent as possible so that you can try out the techniques mentioned in your choice of software.

Introduction

Design, modeling, surfacing, lighting, animation, rendering and post-processing—these are some of the aspects that we generally look at during the span of each project. For most of the people that I have come across, the greatest stress has been on modeling and it declines as we move on to other aspects. The most neglected aspect is that of proper lighting. Place a few lights here and there and then relying on the software’s rendering engine will only get you so far as to come up with a synthetic (in other words, pathetic) looking image. The goal for some of us is photo-realism, and that requires not good modeling, but good surfacing and good lighting. It is easy to get away with images that require artificial lighting because we are not that familiar with it when compared with natural lighting. Replicating sunlight inside your 3D software is hard. The audience, being familiar with sunlight, is very quick to point out any irregularities. Certainly, those who are in the business of replicating sunlight need to be extremely observant of how natural light reflects, refracts, changes color, and changes intensities in nature. Simulating natural light requires a lot of consideration regarding the position, intensity, and color of the light sources used.  

Some Characteristics of Light

Color

The color of light depends upon its source. White light is composed of all the possible colors that exist. A ray of white light changes color if it encounters an obstacle, which is not white and is not black. If it hits a white object, the same ray is reflected. If the object is black in color, all the light, no matter what color it was originally, is absorbed by the object and nothing is reflected. So basically when you look at a totally black object, you see the color black because no light enters your eye from that direction. To prove this thing, I ask you to close your eyes for one second. Which color did you see?

In Fig. 1 below you can see a white incident ray of light, which is reflected off a blue floor. The floor absorbs all the colors in the incident ray except blue, and reflects it. Note that the light is reflected at the same angle at which it was incident relative to the floor.  

Fig. 1

Any object that is in the path of the reflected blue ray will be lit by blue light only, provided that the white light is not incident on the same object. If it is, the object will have a blue tinge.  This blue tinge is caused by radiosity, a phenomenon that is not implemented in most 3D software because of the tremendous mathematical complexity of radiosity algorithms.