Focus On Photon Mapping (Premier Press Game Development)

2017-07-07 02:10:07

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Understanding the Electromagnetic Spectrum

The electromagnetic spectrum is a vast array of different types of waves. All electromagnetic waves travel at one constant speed but differ in frequency (and wavelength). The spectrum is divided into segments based on each wave's frequency. Unique frequencies relate to unique wavelengths . Low-frequency waves produce a long wavelength, and higher-frequency waves have a shorter wavelength.

A simple way to understanding the electromagnetic spectrum is to divide the spectrum into ten parts. Parts one to four refer to radio vibrations, four to eight refer to light vibrations, and eight to ten refer to gamma vibrations. Now in order to find a particular wave, you filter out the relevant waves from the list. Nature does this in a similar way, filtering out which waves are needed from the spectrum. Humankind has harnessed this vast spectrum as well, producing appliances such as TVs, cell phones, AM/FM radios, wireless networking, optical networking, and much more. All of these devices amplify and filter out each type of vibration from the electromagnetic spectrum. The spectrum is not divided into equal segments, and many regions overlap each other.

NOTE

Did you know that electromagnetic waves are all around us moving in and out of our bodies in space? Only a very small portion of the electromag netic spectrum is visible to the human eye.People might therefore think of space as empty,but this is definitely not the case.Space is in fact filled with waves traveling to and fro.

Let's take a look at the following major sections of the electromagnetic spectrum. The spectrum is classified by a number of waves in each section. It is important to understand the different areas of the spectrum because you gain a broader understanding of how light falls into the bigger picture. The nature of light in accordance to the electromagnetic spectrum is also known as the wave model of light .

The following list describes the parts of the electromagnetic spectrum, starting from low frequency, low wavelength waves:

Radio waves fall in the range of a few thousand hertz (vibrations per second). They are considered low frequency radio waves. If you move up to one million vibrations a second, you'll find the AM radio band. After that, you move up to 50 million hertz to VHF (very high frequency) television frequencies. (Remember those old days of TV, when you had to adjust those annoying rabbit ear antennas to improve your picture quality?) The FM radio band falls between 88 and 108 million vibrations per second. Finally, there is UHF ( ultra high frequency), which occupies the high end of the radio spectrum. Today, some radios and televisions use these frequencies.

Microwaves operate around one billion vibrations per second. Today, we use these waves in microwave ovens, which decrease cooking times dramatically.

Infrared waves are also commonly referred to as heat waves and start at around one trillion vibrations per second. Ever wonder how your TV remote control works? Well, almost all remote controls today use infrared. Without your remote control, just think of the hard work you'd have to dogetting up and changing the channel! IR is also used to transfer data wirelessly using infrared ports on laptops. Folks can send data to an infrared-equipped printer from their PDA devices as well. It's a quick and handy way of working around a local area network.

Visible light is a tiny percentage of the electromagnetic spectrum, but it's all we can see around us with the naked eye. Visible light waves vibrate at around 430 trillion times per second. The lowest frequency of light our eyes can see is red followed by orange, yellow, green, blue, and finally violet (remember ROYGBIV?). Violet 's frequency is close to double the frequency of red.

Ultraviolet rays, x-rays, and gamma rays, can be hazardous to humans because they have such high energy levels. They are generated in the cosmos naturally as the result of highly energetic reactions such as those found in stars (we can also generate them synthetically with the proper equipment). For example, ultraviolet rays can cause sunburn; hence the need for sunblock. The '70s TV show The Incredible Hulk was about a man who was exposed to gamma radiation, which caused him to turn into a horrific-looking beast . Of course, this isn't relevant to the book, but it's peculiar to see how imaginary stories can originate from some essence of scientific fact.

Light and sound are vibrations found in the electromagnetic spectrum that travel throughout space. Sound is the spreading of vibrations through a physical formanything that is solid, liquid, or gas. Light is generated only by electrical and magnetic fields. In a vacuum (without any gravitational warp-ing), light travels in a straight line from one point to another. It is important to remember that all waves begin from vibrations of some sort .

NOTE

TV stations,radio stations,and cell phone stations are constantly emitting waves in local cities.Some people fear that these waves can cause long- term danger to us humans because we are con stantly interacting with them.

Newton's first law states that anything in motion will stay in motion and will move in a straight line, unless something else causes it to stop or change direction. This is the nature of light, which will travel forever unless stopped or blocked. Today we can see the destruction of stars that occurred millions or billions of years ago. This is because the light takes many years to travel into our field of view. Countless trillions of light beams travel from the sun to the Earth every day.

Transparency

Transparency is one of the most amazing effects in nature. We have transparent objects all around us. We have clear glass in things like vases, ornaments, windows , and bottles. We also have transparent plastics like Zip-lock bags and Saran wrap. We have clear water in a pool or a glass of water. Transparency is everywhere, and most of us fail to realize its presence.

Transparency is basically when objects allow light to pass through them.

Electromagnetic waves travel in straight lines from one point to another. Now, if for any reason, the wave interacts with some type of matter, some of the electrons in the matter start to move and vibrate. Picture some small children playing, running back and forth. When they accidentally run into each other (which they always do), they cause each other to shake based on their force. Similarly, matter reacts to light based on the matter's properties and the light's frequency. When the light hits an object, it causes the electrons in the object to vibrate (see Figure 1.4).

Figure 1.4. Light waves have both wave-like and parti- cle-like behavior,as discovered by Einstein.

In the representation shown in Figure 1.4, electrons are connected to atoms by what look like springs. The springs stretch and move because of the source vibration from the light waves. The incoming energy is either converted to heat and is spread out to the neighboring atoms , or it's retransmit-ted as light.

The wave's frequency determines which vibrating electrons are trapped and which ones break out of jail. The lower the wave frequency, the less time the atoms in the material hold onto the vibrating electrons of the wave. This causes the wave to have less interaction with neighboring atoms, thus allowing the wave to move faster. And because the wave moves faster, some of the energy slips through the material to the other side.

The clear glass in a window is almost perfect in distributing this incoming energy, as illustrated in Figure 1.5. The frequency in which the light hits the window is identical to the way the light is retransmitted from the window. The main point to focus on here is the time it takes for the light to travel from one side of the glass to the other.

Figure 1.5. Light travels through clear glass more or less unencumbered.

When light travels inside of materials, its speed varies. Remember, light waves travel at around 300,000 kilometers (or 186,300 miles) per second, but that assumes it is traveling through a vacuum. When light travels through water, its speed is 75% of that. When light travels through a diamond, its speed is reduced to 41% of that. As a graphics programmer, you must study all of this information and try to simulate it using 3D algorithms. I am still trying to find an engineering materials book to fully simulate real-world models in nature.

So now you've learned that light's continuous progress through an object is based on the object's properties and the light's frequency. Let's consider some more light- related properties that objects can have.

Opaqueness

In Adobe Photoshop, you change the opacity of a layer to make it more or less transparent. A setting of 0 makes the layer totally transparent, and a setting of 100 makes it totally opaque .

Opaque means to block the passage of radiant energy, especially light. Almost everything around us is opaque.

Opacity and transparency work hand in hand. Consider objects that absorb light without any retransmission. Objects like walls, chairs, people, books, furniture, and oranges are all opaque. If an object is 100% opaque, it absorbs 100% of the light it receives.