What is Light and How is it Produced (page 2)

By — Pearson Allyn Bacon Prentice Hall
Updated on Apr 30, 2014

Visible Light

As previously mentioned, visible light is the small range of electromagnetic radiation that is detected by our eyes.

The spectrum of visible light is further subdivided into various colors, with red having a longer wavelength and violet having a shorter wavelength. The colors are separated into the basic colors of red, orange, yellow, green, blue, and violet, ROY G. BV. Often a vowel is added to BV, making it BIV with the I standing for indigo. However, in recent years, the inclusion of indigo has been discontinued.

The Speed of Light

Visible light and all electromagnetic radiation travel at the same speed. This speed is measured by many different methods. The speed of light in a vacuum is normally rounded to 300,000 kilometers per second or 186,000 miles per second.

Light travels in a straight line. However, if it could curve around Earth, it could make more than seven trips in 1 second. Light can travel to our Moon in just over 1 second. It takes light from the Sun approximately 8 1/2 minutes to get to Earth.

Examining light from stars becomes an interesting process. Our nearest neighboring star is Proxima Centauri, which is visible in the Southern Hemisphere. Even though it is the nearest star, it takes the light from that star 4.3 years to get to Earth. Other objects in our sky, such as some distant galaxies, are so far away that it takes 13 billion years for the light to reach us. That means that we see that galaxy as it was 13 billion years ago.

The Normal Sighted Eye

The eye is an amazing organ that detects and positions light so that we can see. Our eyes collect light so that we can see. Our eyes collect light energy that travles through the lens of the eye and is detected by the retina. These responses are sent to the brain where they are decoed into vision.

The light receptors of the eye are of two types: cones and rods. Cones are specialized cells that not only detect light but also measure the wavelength so that the color of the light is recognized. Cones are concentrated at the fovea area of the retina. Rods detect light and are concerned with black and white vision. Because rods cover most of the retina, the objects that we see at the perimeter of our sight tend to be viewed as black and white. The objects viewed at the center of our vision tend to be more color vision.

For detecting dim objects, the rods are more critical because they do a better job of collecting light. It is interesting that observational astronomers watching stars in the nighttime sky tend to look at an object a few degrees away from the star they are viewing so that the rods come more into play than the cones. The object that they want to see will become much brighter than if they looked directly at the object.

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