The Nature of Light
This is the first part of the tutorial on iridescence. This new series will explore the very nature of light, in order to understand and to replicate how material exhibits colourful reflections. The tutorial is oriented to Unity game developers, although the techniques described can be easily implemented in other languages, including Unreal and WebGL.vi
Iridescence is an optical phenomenon which causes objects to change colour as the angle of illumination or the angle of view changes. It is because of this effect that bubbles appear to display such a variety of colours.
Iridescence can also occur on spilt oil, CD-ROMs, and even on fresh meat. Many insects and animals use iridescence to create colours, without the need for actual pigments.
This is because iridescence occurs from the interaction between light and the microscopic structures that all those things have on their surfaces. Both the tracks of a CD-ROM and the scales of an insect’s exoskeleton (images below) are on the same order of magnitude of the wavelengths of light they interact with. Iridescence, in fact, is possibly the first phenomenon to be discovered that really betrayed light’s real nature as a wave. We cannot either explain or reproduce iridescence without first understanding what light really is, how it works and how is perceived by the human eye.
Like most subatomic particles, light simultaneously exhibits behaviours that are commonly associated with particles and waves. It is not uncommon to see light modelled as either one of those. For most applications, light can be seen as made of trillions of individual particles, called photons. Most shaders, for instance, assume photons behave like tiny billiard balls, bouncing on objects with the same angle they hit them (diagram below).
