Is looking at a bare mercury lamp light dangerous?

[Roger Breton]

To which Victor replied:

Well, my answer may very well start a flame war

As far as I am concerned, a neon lamp contains ----neon as the active
gas. However, there are some people who believe that any lamp with
cold electrodes, and certainly any lamp with cold electrodes that is
bent into interesting shapes, is a "neon" lamp, even if the lamp does
not contain a single atom of neon. These lamps produce colors other
than the characteristic neon red color because they use gasses other
than neon.

On the other hand, there are "real" neon lamps that use a phosphor to
convert the small amount of UV produced by the neon discharge into
other colors. These are still neon lamps, IMHO. However, there is very
little useful UV produced by a neon discharge, so the phosphor output
is rather weak. I would assume that a "neon" lamp that does not have
the neon color is using other gasses.

Is the wavelength of neon around 660nm? Can I use that as a criterion in my
search for a 'real' neon lamp?

Roger Breton

 

[Victor Roberts]

Is the wavelength of neon around 660nm? Can I use that as a criterion in my
search for a 'real' neon lamp?

Real neon lamps are easy to spot. There is no other gas that has the
color of neon, in my opinion at least. I may confuse argon, krypton
and xenon, for example, because they are all sort of blue-white to
pink-white and I am a bit color blind, but neon has a distinctive
red-orange color. If the emission is rich in line spectra, as opposed
to bands from a phosphor, and the color is red-orange then it will be
neon.

There is a strong neon line at 640nm, plus a slightly weaker line at
660nm. Other relatively strong neon lines are at; 540nm, 585nm, 588nm,
603nm, 607nm, 614nm, 616nm, 622nm, 627nm, 633nm, 638nm, 693nm, 703nm,
717nm and 725nm. There are more lines beyond 800nm but they will be
hard to see with the human eye.

 

[Roger Breton]

To which Victor replied:

Real neon lamps are easy to spot. There is no other gas that has the
color of neon, in my opinion at least. I may confuse argon, krypton
and xenon, for example, because they are all sort of blue-white to
pink-white and I am a bit color blind, but neon has a distinctive
red-orange color. If the emission is rich in line spectra, as opposed
to bands from a phosphor, and the color is red-orange then it will be
neon.

There is a strong neon line at 640nm, plus a slightly weaker line at
660nm. Other relatively strong neon lines are at; 540nm, 585nm, 588nm,
603nm, 607nm, 614nm, 616nm, 622nm, 627nm, 633nm, 638nm, 693nm, 703nm,
717nm and 725nm. There are more lines beyond 800nm but they will be
hard to see with the human eye.

OK. I need to locate these pure neon gas lamps then. No question. Thank's
for your help, Victor.

As an aside, what do I interpret the more or less weak spectral liines to
be? Is it an indication of the level of energy at a certain wavelength? I
think I remember reading that each spectral line reveals the atomic
composition of the material in question. So, with my limited chemistry
knowldege, would you say that each of the the neon spectral lines you
enumerated above correspond to a particular atom being excited in the neon
gas? (I will look at the atomic structure of neon in the periodic table) And
would you say that the height or strength of each line is a function of the
quantum of evergy release by that particular atom?

Hope I don't mix all these different concepts too much.

Best regards,

Roger Breton

 

[Victor Roberts]

As an aside, what do I interpret the more or less weak spectral liines to
be? Is it an indication of the level of energy at a certain wavelength? I
think I remember reading that each spectral line reveals the atomic
composition of the material in question. So, with my limited chemistry
knowldege, would you say that each of the the neon spectral lines you
enumerated above correspond to a particular atom being excited in the neon
gas? (I will look at the atomic structure of neon in the periodic table) And
would you say that the height or strength of each line is a function of the
quantum of evergy release by that particular atom?

Hope I don't mix all these different concepts too much.

All the lines I listed are from neon, that is atomic neon. The
different lines have different wavelengths because they are generated
by transition between different energy levels of the neon atom. The
strength of the line is a function of the population of the upper
level (and sometimes the population of the lower level if it is high
enough) and the transition probability for the transition from the
upper to lower level. In a normal gas discharge the upper levels have
lower populations than the lower levels since the levels are populated
by collisions between the neon atoms and electrons and there are
fewer higher energy electrons than lower energy electrons. Certain
special discharges, such as He-Ne as used for He-Ne lasers can create
a population inversion in certain pairs of energy Ne levels that are
essential for the laser to function. So, lines that originate at
higher levels are generally weaker than lines that originate at lower
levels. However, the transition probability also comes into play, so
some lines that originate at relatively low levels can be weak because
the transition probability is low.

It is the combination of emission lines that is used to identify a
particular atom. Each atom has a unique emission "signature" and this
can be used to identify which atoms are present and radiating in an
object.

 

[Jerry G.]

It is not recommended to look at these lamps directly without some type of
eye protection. Even though the outer case of the lamp is glass, there is
still very high UV emission. If you can have safety goggles for all the
people involved, this would then be okay. Keep exposed skin covered when
near to the lamp.

Even though the lamp emits a large amount of visible light, and forces the
iris of the eyes to close down, the UV emission is still too high for
safety. When the lamp is put through the proper outer cover and is a fair
distance from the observer, it is a safe.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
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I am thinking about setting up some observation experiments with my students
and the help of a spectroscope I bought from Edward Scientific to
demonstrate the dicontinuous spectral nature of some light sources. I was
thinking of observing a 175W bare mercucy lamp and a 150W sodium lamp
because those, I think, would be most revealing as compared to observing the
spectrum of a tungsten lamp. But someone told me that directly observing a
mecury lamp would be dangerous? I don't want to make myself or any of my
students blind because of my ignorance.

Any suggestions? Comments?

Roger Breton

 

[Loren Coe]

It is not recommended to look at these lamps directly without some type of
eye protection. Even though the outer case of the lamp is glass, there is
still very high UV emission. If you can have safety goggles for all the
people involved, this would then be okay. Keep exposed skin covered when
near to the lamp.

this really sounds like a good, long term, solution for an educator.
the goggles would be part of the "experiment", lab equipment, kept
for subsequent presentations.

it would also give proper guidance for youngsters. --Loren

 

[Roger Breton]

An interesting and educational spectral demonstration is to look at the
spectrum of an HPS lamp as it warms up. As the light output increses, the
original low pressure sodium lines are absorbed and replaced by a gap with a
broader spectral discharge on either side. From the safety standpoint,
there is no UV emission from the lamp and a 50 or 70 watt HPs lamp provides
plenty of light.

By the way, it is not difficult to project such spectra on a large screen so
a whole classroom can see the demonstration at once. You need a light
source, an enclosure with a hole to let some of the light out, an adjustable
slit and a diffraction grating arranged so that you can adjust the distance
between the grating and the slit (for focusing). Make a slide with a
wavelength scale and project that on the screen below the spectrum and you
have a way to identify the lines.

Image quality is a direct function of the quality of the diffraction grating
and the adjustment of the slit.

Terry McGowan

Terry,

Any idea of what the warm up time is like on starting a High Pressure Sodium
lamp? Is it in a manner of minutes, 5 minutes, 10 minutes or an hour?

And once the kight output has increased and that the original low pressure
sodium lines are absorbed and replaced by a gap with a broader spectral
discharge on either side, what kind of spectrum will that give? Continuous
or discontinuous? Can I expect that the image in the spectroscope will be
"empty" up to 600nm where the wide spectral bands of sodium discharge will
apear?

Regards,

Roger Breton

 

[TKM]

Terry,

Any idea of what the warm up time is like on starting a High Pressure Sodium
lamp? Is it in a manner of minutes, 5 minutes, 10 minutes or an hour?

And once the kight output has increased and that the original low pressure
sodium lines are absorbed and replaced by a gap with a broader spectral
discharge on either side, what kind of spectrum will that give? Continuous
or discontinuous? Can I expect that the image in the spectroscope will be
"empty" up to 600nm where the wide spectral bands of sodium discharge will
apear?

Regards,

Roger Breton

The warm-up of an HPS lamp takes 1-2 minutes depending upon the lamp
wattage. That's just enough time, from my experience, to describe to
students what's going on.

As the HPS spectrum broadens out, a low-level continuum appears, so the
spectroscope image won't be "empty". Lines are also apparent - especially
one about 500 nm. Those who think that sodium lamps don't emit blue or red
wavelengths are surprised to see regions of both. Using a "deluxe" or
"improved-color" HPS lamp makes an even better demonstration because the arc
operates at higher pressures and the continuum has more output especially in
the red regions. As Vic noted in another thread, the standard HPS arc tube
pressure is 1x10^4 Pascals. The deluxe type operates at 4x10^4 Pascals.
Standard and deluxe HPS lamps of the same wattage can be interchanged on the
same ballast.

Terry McGowan