Light is a small band of frequencies visible to humans in the larger scale of electromagnetic radiation. It has different properties depending on its amplitude and wavelength, with longer waves producing red light and shorter waves producing blue. Light has a dual nature as both waves and particles, and travels at a constant speed of 186,282 miles per second. Infrared light is used for night vision and thermal imaging, while ultraviolet light is used in crime science to make bodily fluids fluoresce.
Light refers to a small band of frequencies visible to the human eye in the larger scale of electromagnetic (EM) radiation. Most electromagnetic waves oscillate at a rate that humans cannot detect visually. This could be compared to a dog whistle with a pitch that human ears cannot hear. Similarly, some animals can see EM frequencies that humans cannot. Bees, for example, see in the ultraviolet (UV) range to locate patterns in flowers visible only with UV-equipped vision.
EM radiation is an electric field with magnetic properties that travels from one point to another or radiates outward. EM radiation is a wave with frequency and amplitude. Frequency refers to how many waves pass a stationary point per second, while amplitude measures the height of a wave. Visible light has a wavelength of 400 to 700 nanometers. To put this into perspective, a nanometer is one-billionth of a meter (one-billionth of 3,281 feet).
Light has different properties depending on its amplitude and wavelength. Longer waves, or lower frequencies, produce red light, while shorter waves, or higher frequencies, produce blue. Red is at one end of the visible spectrum, while blue or violet light is at the other. Just beyond the blue/violet spectrum are ultra-short waves called ultraviolet. This barely visible and nearly visible light is also called high-energy ultraviolet (HEV) light.
At the blue end of the spectrum, most of the radiation becomes invisible, resulting in a faint violet light, also called black light. This wavelength has interesting properties in that some pigments absorb extra radiation that cannot be seen, causing these pigments to re-radiate the energy and glow. An example is a black light poster. The slightly shorter wavelengths produce black light used in crime science to make bodily fluids such as urine and blood fluoresce. In addition to UV radiation on the EM scale there are X-rays and gamma rays. Cosmic rays, when included, fall here; although many scientists believe that cosmic rays do not technically belong to the EM spectrum.
The opposite end of the visible spectrum goes beyond red to infrared. Infra is Latin for “under”, so infrared literally means “under the red”. Infrared light is used for night vision and thermal imaging cameras. In this wavelength, hot objects appear brighter than cold objects. Infrared is also used for short-range networking of computer peripherals with the Infrared Data Association (IrDA) specification. As wavelengths continue to grow, we reach microwaves, followed by radio waves, and finally the broadcast spectrum.
Although light is often described as a wave, it has a dual nature according to quantum physics. Physics describes light as photons or massless particles of energy that can sometimes behave like a wave. Whether waves, particles or vibrating “strings,” as superstring theory suggests, all EM radiation moves in a vacuum at a constant speed of 186,282 miles per second, or 299,792,458 meters per second. A light year is therefore the distance that light can travel in one year. The closest star, Alpha Centauri, is four light-years away.
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