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

Light and Energy

  1. Mar 17, 2003 #1
    what is the difference between a phosphorescent source and a fluorescent source?

    How does a flashlight can be luminous? How can it also be nonluminous?

    Which kind of light source would be safest to use in building or mines that may be filled with explosive gas?
  2. jcsd
  3. Mar 17, 2003 #2


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    phosphorescence is more persistent (Websters)

    might try webster's for starters:

    flourescence is emission of EM radiation (usually visible light)
    occurring ONLY DURING the absorption of radiation from some other source [quote from Webster's, with my emphasis on the only during]

    phosphorescence is luminescence caused by absorption of radiation which persists for a noticeable time AFTER the stimulating radiation has stopped [my emphasis on the after]

    phosphorescence can also mean a cold light from some chemical reaction, I believe, anyway some kind of production of light without noticeable amount of heat. But that is the secondary meaning.

    the main thrust of what webster's has to say is that flour. and phosph. are pretty much the same idea-----just that phosphorescence is more persistent. Typically both are caused by absorption of some more energetic type of light-----UV for example.

    A fluorescent light tube works by making UV inside the tube and having the UV get absorbed in a white coating on the glass and that coating shines with visible light---it fluoresces. And when you turn it off, the production of ultraviolet inside stops almost immediately and also the flurorescence stops.

    But an example of phosophorescence are those plastic stars parents give children to stick on the bedroom ceiling. They get irradiated by ordinary room lights. Then you turn off the room lights and they glow this dim greenish white color for a while.
    It lasts for a good 15 minutes, as I recall. Then you have to turn the lights back on to give it another dose of energy.

    YOU SHOULD go to your local bicycle shop and have them explain
    the nokia white LED bike headlight. That is a really great light source. It runs on, like a few volts of battery power. It is cool. No sparks, no hot filament. A beautiful idea----a blue solid-state light embedded in a yellow fluorescent plastic. Some of the blue comes thru and some of it excites the fluorescent dye in the plastic making it glow yellow. So what comes out is a mix of blue and yellow and it looks white. Find out, I urge you, it is a great light source---only on the market since 1998 or so, I think.
  4. Mar 18, 2003 #3
    I suppose phosphorescence originally meant the emission of photons from a source of phosphorus recently subjected to illumination. Phosphorescence now applies to any substance with such property.

    Fluorescence may have originally applied to fluorine, an element so reactive as to produce light (and heat!) upon interaction with most substances. The current usage of "fluorescence" may apply to the production of light by direct application of chemical or other non-thermal energy.
  5. Mar 18, 2003 #4


    User Avatar

    There's also incandescence, the property of a body so hot its blackbody radiation emits visible light. Obvious examples are ordinary tungsten lightbulbs, red ambers and so forth.
  6. Mar 18, 2003 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Fluorescence happens when a substance absorbs one wavelength of light, and re-emits a lower one. (essentially, the Shorter wave length photon causes an electron to jump up a number of energy levels, and then the electron returns to its initail state, on energy level at a time.)

    I believe it got its name from the mineral that first displayed this characteristic, this is the same mineral from which flourine was separated from, so flourine got its name form the same mineral. The Mineral was named after the region where it was first discovered.
  7. Mar 18, 2003 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Phosphorescence differs from Fluorescence in the fact that it continues even after the initial light source is removed.

    The term Phosphorescence comes from the Greek for "light bringing" (Which was also the name given to Venus when it was the Morning star).

    Interestingly, phosphorus, which also gets its name from the same root, exhibits Fluorescence not Phosphorescence.
  8. Apr 6, 2004 #7

    how can a flaslight be nonluminous ?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook