Properties of Light Light is an electromagnetic wave which propagates through space. Below is a representation of what this process looks like. Pictured in green, the electric field (E) propagates perpendicularly along our vertical field of view while the magnetic field (B), in purple, propagates back and forth across our horizon.   i. Light Speed (a universal speed limit) Light is always racing, it never slows down. It's almost like it just doesn't have the time to. It’s the fastest propagating thing in the universe known to humankind, traveling at approximately 300 million meters per second. At this speed, light can circumnavigate the planet earth seven times in a single second, and travel the distance of ~93 million miles from the star at the center of our solar system, into our eyes on earth in just under 9 minutes. For reasons unknown, although many theories attempt an explanation, nothing can go as fast as light. Einstein’s theories of Relativity beautifully illustrate this universal speed limit, painting a relativistic picture of space and time. Unfortunately, I lack the ability to articulate these theories in detail, so I shall leave it to the reader to further explore this subject if they wish for a broader understanding. For now it will suffice to note that light (electromagnetic waves), itself considered “massless”, is the only known aspect of the universe to travel at lightspeed. No particle of mass at any distribution is known to humankind to be capable of reaching and/or exceeding this speed limit. In practice scientists have attempted to defy this law, only to ultimately demonstrated an asymptotic approach to infinity of the necessary propulsion energy required to accelerate mass (however small) to the speed of light. Particle physicists have managed to accelerate particles to 99.999999% the speed of light in their attempts to test this cosmic barrier. The results of these experiments, alongside numerous more, directly demonstrate aspects of Relativity foundational to Einstein's predictions about the nature of the universe, and the implications of the speed of light in the grand scheme of a unified theory. ii. Light as a Spectrum Light exists on a spectrum of wavelengths, ranging from short wavelength gamma rays to long, drawn out radio waves. Between these extremes lies the spectrum of visible light (light that the human eye can register). Wavelength is a fancy word for frequency, where frequency denotes how often a we see a complete cycle of osculation in a given electromagnetic wave. To determine the wavelength (λ), all we must do is measure the distance between consecutive peaks of a coherent wavelength (light of a single color), as diagrammed above. In yellow, we see that the wavelength of λ1 is longer than the wavelength of λ2 illustrated in blue. This means that  λ1 is less frequent than λ2. The range of color of visible light will spread from red to violet, like a rainbow, as we progresses along the spectrum, from lower frequencies (larger wavelengths) to higher frequencies (shorter wavelengths) respectively. To picture the scale of visible light imagine a meter: this is a relatively short distance, but it is not so small as to be intangible. Some would even go so far as to say that if you were to cut a meter into one billion divisions, known as a nanometer (nm), that this distance too, although considerably smaller, is also not intangible. It is on this scale of nanometers that visible light propagates, ranging from the deepest violet with a wavelength of ~ 400nm to the deepest red with a wavelength of ~ 700nm. Illustrated  above: scale divisions of 100 [nm] III. Relative Intensity (Brightness)   Wavelength is only responsible for the color of light: in other words, the wavelength does not tell us how bright a light is. Brightness is dictated by the amplitude (better known as the height) of a given wave, as illustrated in image A. below: Wave "a" (top) has a smaller height than wave "b" (bottom) and therefore  we can conclude that "b" will appear dimmer than "a". ~note that the lights will appear as the same color because they are still the same wavelength. A.                B.  In image B. we see what intensity/brightness represents as it relates to our surface-level interactions as observer. Brightness is simply the number of photons (light as defined in a quantized state) that are emanating from a source. The brightness varies for given viewpoints, depending on its orientation relative to the source. The number of photons around a given light source will drop off by a factor of one divided by the radius (R) squared: [ 1/(R)^2 ]. This essentially means that the further you are from a light source, the less light will be able to reach you, and therefore the less bright that light source will appear to you. <index   <1 , 3> , 4> , reference>