Michael Belden, age 12, of New Hartford, N.Y., for his question:
HOW IS LIGHT PRODUCED?
Can you imagine what the earth would be like without light? Only part of the problem would be the fact that we wouldn't be able to see, since light that comes to our eyes makes seeing possible. The simple truth is that we couldn't live without light since we would have no food. Green plants use the light from the sun to grow and make food, and all the food we eat comes from either plants or animals that eat the plants.
Light is a form of energy that can travel freely through space. Sources can be either natural or artificial, but all of it comes from tiny particles of matter called atoms. Atoms release and absorb energy in tiny bundles called photons. Light consists of streams of photons.
Does that sound complicated? Well, you're right. It is complicated.
Think of it this way: The higher the energy level an atom reaches before it drops back and releases a photon, the more energy that photon will have. All photons do not have the same amount of energy. Photons with different amounts of energy make up different colors of light. Blue light requires the most energetic light photons while red light takes the least. White light takes a mixture of photons with energies that cover the whole range of visible light. As a result, white light consists of all the colors of light.
Atoms can be excited in a number of ways to give off photons. It can be done with heat, for example. A hot piece of iron taken from a furnace will glow white hot. The white light changes to red as the iron cools a bit and becomes red hot.
The sun, of course, is our most important source of light. The energy that excites atoms in the sun to emit photons comes from atomic reactions inside the sun that change matter into energy.
Photons of light act much like streams of particles, such as bullets being fired from a machine gun. They also act like waves, such as ripples on a pond. Scientists debated for many years whether light consisted of particles or waves. They couldn't understand how it could be both, yet they could not explain all they knew about light in terms of either waves or particles.
Although light seems to be both a particle and a wave, it is perhaps easier sometimes to think of light as simply particles or simply waves.
Whole books have been written on how light is produced, and Andy hopes that at least the surface of the subject has been scratched in these few lines.