The Thursday Ten: Some Light Reading (#blogboost)

Okay, maybe not light reading, more like reading about light.

A friend of mine and I were talking the other day, and he came out with a philosophical question: “What is light?” And I couldn’t answer him. Then I thought, “that would make a great Thursday Ten!” So I found several resources on the Internet, starting with Wikipedia and landing on NASA’s Tour of the Electromagnetic Spectrum. It’s a tremendous resource that I’ve bookmarked and plan to come back to on a regular basis. Anyway, here we go…


  1. Light is electromagnetic radiation. On the electromagnetic spectrum (which includes the radio and TV bands) light resides between microwaves and gamma rays.

    The electromagnetic spectrum (source: NASA)
    The electromagnetic spectrum (source: NASA)
  2. Visible light has wavelengths between 400 and 700 nanometers.
    Color Wavelength (nm)
    Red 650
    Orange 590
    Yellow 570
    Green 510
    Blue 475
    Indigo 445
    Violet 400

    The first letters of the colors spell out the name Roy G. Biv.

  3. Infrared (IR) waves are between 1 and 100 microns (1 micron=1/1,000,000 meter) long. You can feel infrared waves near sources of heat. Night-vision goggles allow you to see thermal images of people and other warm bodies. Your TV remote uses infrared energy to communicate with the TV, and heat lamps use it to overheat food at fast-food restaurants and buffets.

    An infrared light (source:
    An infrared light (source:
  4. Ultraviolet (UV) light is generally expressed in terms of energy, from a couple of electron-volts to 100 eV. Ultraviolet light is what causes sunburn, so make sure you wear sunblock. I’m serious about that. Forensic analysts use UV light to see things like blood residue and other secretions. It’s also used by TV stations to show you how gross hotel rooms are.
  5. Light exhibits properties of both waves and particles. A light particle is called a photon, and it’s a quantum particle. If I were Sheldon Cooper, I’d explain it.


  6. White light is a combination of light of all colors. Sir Isaac Newton noticed that, when white light passes through a prism, you can see the individual colors. This is also the principle behind rainbows, where water works as a prism. You can see the spectrum on Pink Floyd’s Dark Side of the Moon album.
  7. Light travels through a vacuum (for example, outer space) at approximately 186,000 miles per second, or 299,792,458 meters per second. Rounding it to 300 million meters per second make calculations a whole lot easier.
  8. A light year is the distance that light travels in a year, about 9.4605284 × 1015 meters. A parsec is 3.26 light-years. The closest star to the Sun is Proxima Centauri, about 1.3 parsecs or 4.24 light-years away. That means, when we see light from Proxima Centauri tonight, we’re seeing light that happened in May 2010.
    Proxima Centauri, as seen through the Hubble Telescope (source: Wikipedia)
    Proxima Centauri, as seen through the Hubble Telescope (source: Wikipedia)
  9. The refractive index of a medium is an indication of how much light is slowed by it. Glass has a refractive index of 1.5, and light passes through it at about 124,000 miles per second. Water’s index is 1.3, and air’s is 1.0003. I’m not sure what the refractive index of a glass of water is.
  10. LASER originally was an acronym for “Light Amplification by Stimulated Emission of Radiation,” but it’s more commonly written in lowercase (capitalized at the beginning of a sentence) today. A laser produces a spatially-coherent beam of amplified light that can be focused into a tight area, making it good for laser cutting, lithography, laparoscopic surgery, pointing things out on a screen in a darkened room, groovy light shows, and driving your cat insane.


And there’s your Thursday Ten for July 17, 2014.

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