A "Light-Hearted" Discussion
You can be light-hearted, light headed, light-fingered, or light on your feet. You can make light of things, bring secrets to light, or hide your light under a bushel. You can be quick as a flash, moving at lightning speed. You can seek the bright lights or trip the light fantastic. You can see the light and achieve enlightenment - or you can be completely in the dark.
Light - the stuff that's coming from this screen as you read - is a much used metaphor and a puzzling sort of thing. What is light? And what is it about the light coming from this screen that lets you read the text?
The first definition that the dictionary gives is: light is "something that makes things visible or affords illumination," a vague and unsatisfying definition that circles around like a dog chasing its own tail. Physicists define light as electromagnetic radiation - a traveling energy wave produced by a vibrating electric charge. Because light has the properties of a wave, we can talk about its wavelength and frequency. The light that our eyes can see - the visible spectrum - is a narrow band of wavelengths in the electromagnetic spectrum, which also includes radio waves, x-rays, ultraviolet light, and infrared radiation.
Light and other electromagnetic radiation moves fast, speeding along at 186,282 miles per second, much too fast for you to perceive its movement. Since you can't see light move, thinking of it as a moving wave can be a little difficult. And though thinking about light as a wave is very useful for some purposes, it's not very helpful if you just want to know why you can't read in the dark.
In these pages, we hope to shed new light on the subject of light. We'll start with a definition that you will not find in the dictionary: light is information. This information is rushing past at 186,282 miles per second, ricocheting off the walls, bouncing around like mad, and, sometimes, hitting you squarely in the eye. When you take away light you take away information. In a darkened room, you can see little or nothing of your surroundings. Little or no light means little or no information.
Consider a photographer taking a color photo of a class of students. With a camera, film, and a little bit of light, the photographer can take a snapshot that contains a great deal of information: you can look at the picture and count the students or determine what color shirt someone wore that day. Where did this information come from? It wasn't on the film or in the camera. The information was in the light.
The dictionary defines an image as "a physical representation of a person, animal, or thing, photographed, painted, sculptured, or otherwise produced." The photograph of your class is a static image containing much of the information carried by the light. Whenever you look at your surroundings, you gather visual images - the light entering each eye makes an image on your eye's retina. Even though you can't see light move, you can directly experience the images it produces.
Rather than defining light as information, we could say that light is images. You may prefer to say that light carries information and makes images, but whichever phrasing you choose it's clear that light, information, and images all go together.
These web pages will introduce you to activities that reveal the images carried by light, letting you experience light in a new way. You may not come away from your computer with a succinct verbal definition of light and images, but you should gain an understanding of light and become more aware of the images all around you: your reflection in a mirror, the enlarged image you see through a microscope or a telescope, the multiple images that you see when the moon reflects on rippling water. We hope that these activities will help you find a new way of looking at light - a new way of seeing the world around you.