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Old 27-01-2003, 01:24 PM
Dwight Sipler
 
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Default more than you wanted to know about fluorescent lamps

wrote:

--myth. fluorescence do have full spectrum. Ingrid

Florescents do NOT provide full light
spectrum....






How lamps work:

The incandescent lamp works by heating a filament to a high temperature.
The filament then acts as a "black body", producing a spectrum
characteristic of the temperature of the filament and independent of the
material the filament is made of. The spectrum is heavily weighted
toward the red and infrared due to the limitations of the material used
for the filament. The efficiency of incandescent bulbs is fairly low,
since most of the energy is emitted as infrared light or heat.

The fluorescent lamp is a discharge lamp. It is a tube filled with a
gas. An electric current is passed through the gas, which adds energy to
the atoms of the gas. The atoms then radiate light at wavelengths
characteristic of the particular gas used. The wavelengths are fairly
narrow, although they can be widened by increasing the pressure in the
lamp. Most gases that are cheap and easy to use create a set of
wavelengths that doesn't provide a good-looking light, since it will be
weighted toward a particular color depending on the gas used. Some of
the light is in the ultraviolet portion of the spectrum, and this light
is not useful for direct lighting since our eyes don't see down there.
However, this portion of the spectrum can be used to transfer energy
into a phosphor, which is a substance which will emit light when enough
energy is added to it (you may be looking at a group of phosphors if you
have an old CRT monitor). Different phosphors create different spectra,
particularly with different types of gases used in the discharge, but in
general fluorescent lamps use phosphors which look as if they have a
fairly full spectrum, although the actual spectrum is a mixture of the
spectrum of the phosphor and the spectrum of the gas discharge. The
differeent phosphors (e.g. "warm" or "cool") may be weighted toward
different ends of the spectrum, but in general they put out some light
everywhere. The "grow light" fluorescents use a combination of blue and
red phosphors, and are deficient in green light. That's why they look
kind of purple and aren't very good for room lighting.

The fluorescent lamps are more efficient than the incandescent lamps, in
that more of the energy you put into the lamp comes out as visible
light.

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