Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is it Total internal reflection, or something else?

  1. May 8, 2012 #1
    Is this process known as "total internal reflection"? Or is it called something else? What is the name of this process that causes the entire material to light up even though the light is applied only to one side?

    Take a look at the photos so you can see what I am asking about.

    Notice how the light in the key chain is only applied from one direction, yet the entire keychain appears to "light up". Is that caused by total internal reflection?

    I cannot post full links right now so find the picture on tinyurl:

    tinyurl dot com/cu989ek

    You also see it on some exit signs like this:
    tinyurl dot com/dxl2jd2

    A few other examples:
    tinyurl dot com/c58oqsv
    tinyurl dot com/cor6t22

    Wikipedia defines total internal reflection as:"Total internal reflection is an optical phenomenon that happens when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface."

    But that does not seem to be what is happening in the photos I showed you above. From the photos above, the "critical angle with respect to the normal to the surface" does not seem to matter. Or am I missing something here?
  2. jcsd
  3. May 9, 2012 #2


    User Avatar
    Science Advisor

    I don't think you need total reflection for the light to spread around within the acrylic glass. Some of it is partial reflection, but you don't see much of the part that escapes because it is bend towards the surface and you look rather perpendicular to the surface. The edges glow because they are rough and reflect / refract in all directions.
  4. May 9, 2012 #3
    So in order to describe the phenomenon that we see in those pictures, what is the way you would describe it?

    Would this be accurate: "The light refracts through the material, causing it to illuminate."
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook