Wednesday, November 28, 2012

Light for Sight

We hesitate to assign sight to top ranking in the catalog of our bodily senses. That temptation, nevertheless, is strong. What wonders does our understanding of sight provide? And what of our marvelous subjective experience of sight, apart from understanding the physiology of how it works? For our sense of sight to be operative, there must be generation and transmission of light energy through space from a light source. In addition there must be an organ of vision to receive the light energy. In each case, wonderfully complex events complete the process. Complete understanding requires us to grasp physical processes of generation and transmission of light energy as well as the function of the eye and brain in making meaningful visual images spring to cognizance.

In 2009 we posted a series on light, just one manifestation of the bath of electromagnetic waves in which we are immersed each moment of our lives. Before we grasp the beauty of light, the energy form by which we experience vision, we must understand what processes produce light and transport light images to our eyes. Accordingly, I encourage my readers to review my 10-post series on light as a prelude to investigating vision. The series begins with this post:

Each additional article may be accessed with the “newer post” link at the bottom of each entry.

Visible light is transmitted to our eyes through space via “packets” of electromagnetic energy traveling at 300,000 km/sec. At this speed light travels the distance around earth’s equator more than seven times per second. While the speed of light is seldom expressed in speed units of miles/hr, the speed has been calculated as 670,616,629 miles/hr. At that speed light almost covers the distance to giant planet Saturn in the time we need to consume a leisurely evening meal.

How many “packets” of light energy enter our eyes each second? The answer depends on what color light we are observing. If we observe an object giving off red light, 430 trillion “packets” of light pass through our cornea each second. The “packets” of red light are about 1/40,000 inch in length. A physical scientist prefers the term “photons” to “packets of light.” The shortest wavelength is violet light. If we observe violet light, 750 trillion photons enter our eyes each second. Physical scientists tell us violet light has a frequency of 750 trillion hertz (Hz).

In our first lessons on atomic structure we learned that all matter is composed of electrically positive protons, neutrons without an electrical charge, and electrons possessing negative charges. The atoms of all matter are in constant motion from thermal energy. So also are their associated electrical charges. The constant motion of the electrically charged particles is the source of photons. Several types of electromagnetic waves, including light, are continually produced by ordinary matter. In addition physicists have discovered the means for artificially generating a virtually unlimited variety of electromagnetic wavelengths. Their multiple uses range from communications to medical applications.

Electromagnetic wavelengths of visible light, a miniscule fraction of all possible wavelengths, are used in our vision almost every waking moment. Modern technology also uses electromagnetic waves produced by scientists in multiple ways. It is interesting to contemplate what life was like barely two centuries ago before scientists began to make discoveries in respect to the electromagnetic spectrum. Their understanding of the nature, generation, and transmission of light was almost completely lacking but their lives were filled with the everyday luxury of their sense of sight.

The pioneers of the Scientific Revolution could only imagine what discoveries were in store for the human race. Their God-gifted talent, creativity, vision, and dedication helped them discover truths and applications originally conceived in the mind of the Creator and known by him since the universe was created.