The Physical Properties of Light

The visible portion of the electromagnetic spectrum is rather small. Red, green, and blue (the primary colors of visible light) are nested in between infrared and ultraviolet, microwaves and x rays, radio and gama waves. Each band of the e.m. spectrum has a specific wavelength and frequency that define it. We see the visible part of the spectrum because the lightwaves are moving at a frequency our eyes can detect and our brains can interpret. Think of a wave, with its peaks and troughs. Wavelength is the distance between one peak and the next, and frequency is the number of peaks that pass a specific point in a given time. The shorter the wavelength the higher the frequency, or the closer the peaks are to each other the more of them can pass point "x" in one unit of time.

Notice that in the distance from the beginning of the wave to the point indicated, the violet light peaks three times while the red peaks twice. Violet light has a higher frequency and therefore has more energy

Most of the time the light we see appears pretty close to white. There is in fact no white light frequency. White light is what we see when the three primary colors of the visible spectrum (red, green, blue) mix.

Three spotlights shining overlapping cones illustrate the way natural light mixes.

When objects appear to be a certain color it is because some colors are absorbed while others are reflected. A white sheet of paper is reflecting all the colors of light that are hitting it. A yellow pencil is absorbing all the light that isn't yellow so that the only light reflected to our eyes is yellow. A black book cover absorbs almost all light so few colors reach our eyes. When we see white it is the presence of all colors of light reflected. Black is the absence of light (that's why it gets dark when the sun goes down).

 

In the materials lesson I talked about refraction, or the bending of light. Since you now hopefully understand something about wavelengths and frequencies of light we can take a more advanced look at refraction. MAX regards light as a single uniform beam; it's all the same except for the color. That isn't true in the natural world. First of all it is important to understand that a light beam is not just one lightwave traveling on its own. A light beam (even something tightly focused like a laser) is a collection of lightwaves running parallel to each other. In the case of white light the lightwaves traveling in the beam are of different wavelengths and frequencies. Let's take a look at some optics.

Light travels in a straight line until it encounters an obstacle. Once it encounters an obstacle the light can be reflected, refracted, absorbed, or quite often a combination of the three. In the material examples refraction worked to make the spoon in the coffee look bent, and to distort the pattern of a countertop through a drinking glass. Lenses also refract light, bending it in a specific and calculated direction to focus it. Light that passes out of a convex lense is focused into a more narrow beam while light that passes into a concave lense is spread out. The reverse is also true; light that enters a concave lense will be focused and light exiting a convex lense will be spread. (It is the focusing power of lenses that makes it possible to start a fire with a magnifying glass on a sunny day!)

Lenses are designed to focus light in a basically uniform way. Prizms are designed to split light apart. White light enters and is refracted into its component colors.

Light bends because it is slowed down as it passes through a material. The density of the material determines the IOR, but in the natural world refraction is also related to the frequency of the lightwave. In the wavelength and frequency diagram you can see that violet light moves faster than red light. When white light enters a prism and is refracted the high frequency light is refracted more. Think of it like this; the light that is already going (comparatively) slowly is bent less because it is closer to the slowed speed at which it will pass through the material. The fast light is more affected by having to suddenly slow down. Each wavelength is refracted to its own degree and the result is a rainbow.

 

In part 3 of the material tutorials we looked at reflections and reflection mapping. That section related to mirror like and highly reflective surfaces. You now know however, that reflection is also responsible for the colors we see. Light reflects off on object and that reflected light that reaches out eyes lets us see the object. The reflected light also creates what is called radiosity. That is the light reflected off of one object onto another. While MAX does a great job of raytracing reflections it doesn't do radiosity. In fact MAX doesn't direct reflected light at all.

Some of the reflected red light reflected off the ball is reflected again off the plane the ball its on, creating radiosity.

 

Now On to the Solutions!