CHAPTER 1 THE FUNDAMENTALS OF LIGHT O ne of the most familiar and important forms of energy is light Nothing is visible to humans when light is totally absent But light is even more important for other reasons Many scientists believe that mil lions of years ago light from the Sun triggered the chemical reactions that led to the develop ment of life on Earth Without light the living things now on Earth would be unable to sur vive Light from the Sun provides energy for life on Earth Plants change the energy of sun light into food energy When light rays strike a green plant some of their energy is changed to chemical energy which the plant uses to make food out of air and minerals This process is called photosynthesis Very nearly all living organisms on Earth depend directly or indi rectly on photosynthesis for their food energy Some of the energy of sunlight is absorbed by Earth's atmosphere or by Earth itself IO
THE FUNDAMENTALS OF LIGHT Much of this energy is then changed to heat energy which helps warm the planet keeping it in the temperature range that living things have adapted to LIGHT AND ELECTROMAGNETIC RADIATION Different kinds of light are visible to different species Humans see light in what is called the visible range It includes all the colors begin ning with red and continuing through orange yellow green blue and violet Some people can see farther into the violet region or the red region than other people Some animals have a different sensory range Pit vipers for example have sense organs pits that see rays that humans feel as heat These rays are called infrared radiation Bees on the other hand not only see some of the colors that humans see but are also sensitive to ultravio let radiation which is beyond the range visible to humans So though human eyes cannot detect them infrared rays and ultraviolet rays are related to visible light Instruments have been built that can detect and photograph objects by means of infrared rays or ultra violet rays X rays which can also be used to photograph objects are also related to light II
LIGHT The atmosphere causes light to be displayed in breathtaking ways such as during a sunset iStockphoto Thinkstock 12
THE FUNDAMENTALS OF LIGHT Scientists have learned that all these forms of energy and many other kinds of energy such as radio waves microwaves and gamma rays have the same structure They all consist of electri cal and magnetic fields that work together in a special way to form electromagnetic radiation SoURCES OF LIGHT Unlike many other ani mals humans depend primarily on sight to learn about the world around them During the day early peoples could see by the light that came from the Sun but night brought darkness and danger One of the most impor tant steps people have taken to control their 13
