Light

Scholars have puzzled for centuries over the nature and the meaning of light. Light has been thought of as streams of particles since the time of the ancient Greeks. Though no one had actually seen the light particles, scientists assumed the particles simply moved too fast for the human eye to detect, so humans perceived light as a beam or as a field of light. In the 1600s Christian Huygens described light as having more characteristics of waves than of particles. For the next 300 years leading to studies by Albert Einstein, scientists built upon this theory that light behaved like a wave.

Today physicists describe the complex concept of light either as the particle theory or the wave theory. The particle theory states that light consists of beams of photon particles, which Einstein defined as distinct energy packets. The wave theory, also clarified by Einstein, suggested that light is made up of light waves. In fact, light behaves as both particles and waves, but physics students tend to study light in terms of waves because it is easy to understand wave behavior and apply it to light’s characteristics. Lightbulbs serve as a convenient source of light that follow all the rules listed here. The most familiar characteristics of light are the following:

1. Light reflects off surfaces at the same angle at which it strikes the surface.
2. Light waves do not need a medium such as water to travel through (sometimes this is expressed as the ability of light to travel through a vacuum).
3. Light waves radiate from their source, so light is referred to as radiation.
4. Light waves’ energy is in the form of electric fields and magnetic fields, explaining why light can be described as electromagnetic radiation.
5. Light occurs in a range of wavelengths that begin as invisible (to humans), progress into a visible range called the visible spectrum, and end again with invisible waves.

 Light emanates from both incandescent bulbs and CFL bulbs with very little visible difference, but each light source works differently. Any light source produces light by energizing atoms, which causes the atoms’ electrons to behave in an excited state. Electrons are negatively charged pieces of an atom. Eventually, the electrons fall back from their excited state to their normal state in the atom, and this transition from higher to lower energy releases extra energy in the form of a light photon. Incandescent bulbs energize atoms by heating them, which explains why these bulbs become very hot when they are turned on. Fluorescent bulbs use electricity rather than heat to energize atoms. In fluorescent bulbs, an electric current flows from one pole to an opposite pole. During this flow, the current’s electrons bump into mercury (in vapor form) atoms along the path. The energized mercury atoms emit ultraviolet light as they return to a low-energy state; the ultraviolet light hits a compound called phosphor, which then emits visible light.

 Environmental engineers treat light as other scientists do, that is, light is a form of energy and in this form the universe transmits energy from one place to another. Solar homes equipped with light collectors (called photovoltaic cells) convert light energy into other forms of energy, usually electric and heat. Meanwhile humans depend on light’s interaction with their ocular system (the eyes and the nerves connecting them with the brain) to interpret their surroundings. Light has certainly been taken for granted by nonscientists in their everyday routines, but this abundant resource is becoming one of the most promising options for shifting away from dependence on fossil fuel energy. Light energy may soon become the main energy source for cars, boats, appliances, and telecommunications in addition to new solar homes.