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75 w light thats 300 w bright! how do these flourescent bulbs work?

Discussion in 'Electronic Basics' started by max slomoff, Feb 12, 2004.

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  1. max slomoff

    max slomoff Guest


    you always see the claim that these flourescent lights are really
    bright but only use a fraction of the wattage.

    obviously the claim that a light is 300w bright if it only uses 75w is
    an approximation. how accurate is it?

    how do these bulbs work?

    and, if you have 2 150w bulbs shining on the same subject is the
    brightness exactly equal to that of 1 300w bulb?

    thanks for the info,
  2. CC

    CC Guest

    Hi Max,

    It's all radiation. Incandescent lamps emit visible light as well as a
    lot of unseen light in the Ultra Violet and Infrared range. The is why
    you see mostly frosted lights in a house. The coating changes some of
    the Ultra Violet into visible light.

    Florescent lamps start with emitting ultra violet, but are coated with
    phosphors that convert the light into something visible.

    I think the efficiencies are found with the florescent lamps emitting
    less infrared (i.e. heat)

    Hope that helps.

  3. w_tom

    w_tom Guest

    Incandescent bulbs are on the order of single digit
    efficient if the only useful energy radiated is light - as
    measured by lumens. Fluorescent bulbs do light creation with
    about 5 times more efficiency. How fluorescent works is
    summarized by the other post. Notice how inefficient an
    incandescent bulb really is.

    That '300 watts bright' is written so that they can make a
    numerical claim without typical human eyes 'glazing over'.
    Would you notice if they said 300 lumens? Most humans in a
    technical society simply and still don't comprehend simple
    numbers unless those numbers are 'dumbed down'.
  4. Bob Myers

    Bob Myers Guest

    Not so. A "frosted" incandescent bulb is most often just
    that - the inner surface of the glass has been roughened slightly
    to better diffuse the light, so you're not looking straight at the
    glare of the filament. The filament itself has relatively little emission
    in the UV range (practically none), much more in the IR. The
    problem is that incandescence isn't a particularly efficient means of
    producing visible light. The "300W of light from a 75W bulb" is actually
    somewhat misleading - it should more accurately read "You get
    the same light out of THIS bulb (fluorescent) which only consumes
    75W, as you do from an INCANDESCENT consuming 300W."
    The bottom line is that most of that 300W in the incandescent is
    just wasted, as heat.

    Bob M.
  5. Interesting info Bob,

    While I always considered the problem with incandescent lamps as
    excessive IR emission, I could have swore I read somewhere that frosted
    lamps where more efficient than none frosted. Simply diffusing the light
    certainly would not accomplish this.

    "Incandescent light bulbs give off most of their energy in the form of
    heat-carrying infrared light photons -- only about 10 percent of the
    light produced is in the visible spectrum. This wastes a lot of

    Leaves allot to be improved on.... :)


  6. Go where there are clear and frosted versions of the same brand, same
    wattage and same life expectancy. Usually clear and "standard frost" are
    the same in rated light output and "Soft White" is maybe 2.5% less than
    clear and "standard frost".

    - Don Klipstein ()
  7. No, generally a 300W of the same life expectancy and filament style
    produces slightly more than twice the light of a 150W.

    Look at the lumen ratings of various wattages.

    Lower wattages are less efficient for three reasons:

    1. In higher wattage bulbs, a greater percentage of lighting cost is
    electricity cost and a lower percentage is bulb replacement cost. Because
    of this, it pays to run the higher wattage filament filaments hotter for
    greater efficiency despite lower life expectancy.

    2. In higher wattage bulbs the filament is thicker, and at a given
    temperature within a given time a smaller percentage of the thicker
    filament evaporates. The thicker filament can be run hotter for the same
    life expectancy.

    3. In gas-filled bulbs, the heat conduction from the filament by the gas
    is surprisingly proportional to the visibly apparent filament length and
    less than proportional to the visibly apparent overall filament diameter.
    A wider filament has a thicker "boundary layer" of hot gas around it and a
    correspondingly lower temperature gradient. With a thicker/wider
    filament, a smaller percentage of the energy going into the bulb becomes
    heat conducted from the filament by the gas.
    In fact, below a certain "wattage per centimeter" of overall filament
    length of maybe roughly 8-10 w/cm or so, they use a vacuum rather than a
    gas because the gas hurts more than it helps. (When the gas is used, it
    slows down filament evaporation by having gas atoms "bounce" evaporated
    tungsten atoms back onto the filament to permit a higher filament
    temperature for a given evaporation rate.)

    - Don Klipstein ()
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