Let There Be Light

Most of the beauty and wonder of the world is conveyed to us through our eyes and our sense of sight. To know the world through this medium is one of the most marvelous of human faculties. It is made possible because the universe is pervaded by radiant energy, a portion of which we call visible light. Light energy from the sun or some artificial source reflects off of objects and is imaged by our eyes and brain allowing us to see shapes, textures, and colors. Other radiant energy like infrared and ultraviolet is not sensed by our eyes. Infrared is sensed by our skins as warmth while ultraviolet radiation initiates the tanning process to protect us.

Although we do not have biological sensors to detect all radiant energy, scientists have created electronic sensors to detect and measure the whole gamut of radiation from gamma and x-rays through ultraviolet, visible, infrared to microwave and radio waves. All of these are not fundamentally different from each other or from that we call visible light. In fact, they form a continuous band of radiation which differs only in energy content from one end of the band to the other. Scientists refer to it by the esoteric sounding name, the electromagnetic spectrum. Visible light, like the other types of radiant energy, comes from atoms. Atoms are always jostling around and when a collision gives an atom extra energy, the atom is said to be in the excited state. This is an unstable condition and the atom quickly reverts to its normal state by releasing the extra bit of energy in a burst of radiation. Think of the calm surface of water in a backyard bird bath. Drop a pebble into the water and note the ripples that expand out from where the pebble hit. The energy of the falling pebble hitting the water at one spot was dissipated as a wave movement over the surface of the water. Similarly an excited atom rids itself of the access energy by radiating a light wave--a wave that travels at the incredible speed of 186,000 miles per second. Light from a light bulb’s hot filament consists of countless light waves being released by billions of excited atoms.

One important difference between a light wave and a water wave is that the light wave needs no medium in which to make the wave. It can travel through the vacuum of space. The reason for this is that the light wave is an effect not physical substance. An excited atom is one in which one of its negatively charged electrons has gained energy and moved farther from the atom’s nucleus. Every charged particle can be thought of as having an invisible field about it--a field of influence over which the repulsive or attractive effects of the charge can be felt. This field, theoretically, extends out in all directions to the ends of the universe although practically its strength decreases rapidly as the distance from the particle increases. Therefore, the space within and between atoms throughout the universe can be looked upon as permeated with a complex grid made up of the combined fields of all the charged particles in the universe. It is the energy that is transferred as a wave disturbance through this field that constitutes light and all radiant energy. The wave is more complicated than explained here because it has two components; one electric and the other magnetic and this is why all forms of radiant energy is described as electromagnetic radiation.

Scientists characterize the energy content of electromagnetic radiation in several ways. The most common way is to speak of its wavelength--the distance between two crests or two troughs of the wave. Low energy radiation like radio waves have wavelengths measured in meters. While much higher energy visible light has wavelengths of less than a millionth of a meter. Since all waves travel at the same speed, longer wavelengths have lower frequencies (ripples per second) while shorter wavelengths have higher frequencies. In any case, the only difference between one type of radiant energy and another is its wavelength (or frequency). Electromagnetic radiation is a continuous spectrum of wavelengths from the high energy gamma rays at one end through x-rays, ultraviolet, visible light, infrared, microwaves to low energy radio waves at the other.