Fundamentally, light is energy itself, and it is a nature’s method of transferring energy through space extremely quickly. Despite its speed of travel, light does actually have a finite velocity which, in vacuum, is just over 186,000 miles per second (around 300,000 km per second). Despite the fact that this is incredibly fast, light’s finite velocity can be illustrated clearly when we examine huge distances, such as those used in astronomy. As a example, it would take just over two seconds for a radio signal or communication wave traveling at the speed of light to reach the moon and then return.
It is also interesting when you think about light energy in terms of time and perception when watching the sunset or sunrise, or even when gazing at the stars. In terms of that glorious sunrise or sunset remember when you gaze upon it that it actually took place almost ten minutes earlier, as that is how long it take for the light to reach Earth. Also, with respect to star-gazing, the next time you admire Orion’s Belt in the night sky remember that the twinkling stars that appear to be nearby may actually no longer be there! Due to the incredible distance the light energy must travel in order to reach Earth by the time it gets here and you are able to view it the original star may have long since died.
The term “light” is, itself, a little misleading, at least in terms of its actual energy. It is actually more typically referred to as electromagnetic radiation, which is basically the optical light that is visible to us and can be perceived by our eyes. This optical light – or visible light as it is also known – is merely a minute part of a huge range of light on the electromagnetic spectrum. In this range there are X-rays, gamma rays, infra-red and radio, just to name a few. The entire spectrum is simply an unbroken and continuous range of energy.
Within this range, physics has also informed us that light is often represented as a “particle” phenomenon, made up of “packs” of energy called photons. These photons, however, are different with regards to the amount of energy they contain. Every photon of X-ray light, for example, contains more energy than a radio photon. What distinguishes the different ranges of light is the energy content per photon, and as such only specific groups of photons fall within our visual perception range.
The ability to perceive various photons producing different wavelengths of light is also what gives many animals the ability to “see in the dark” as they can pick-up on alternative light wavelengths that standard human eyes cannot perceive. In reality it is impossible to use vision in pure darkness that is devoid of all light, however even at night there are a number of different light waves that exist outside even if human beings are unable to detect and process the energy ourselves.
(Energy FAQ Series)