didymium - sodium light buster + other filters

On Tue, 15 Jul 2003 09:09:32 +0100, Martin Brown
wrote:

In message , Maurice Gavin
writes
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters like...

TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

Ahhhhhhh - Kev judge this subject matter well !!!

That's a very nice way to display higher resolution spectra. How did you
get the colour spectrum to be a decent rendition in colour? My digicams
(and colour films for that matter) baulk at giving an accurate coloured
representation of the monochromatic light at different wavelengths in a
spectrum.

Never had problems with colour spectra - been doing it for some years.

I should declare an interest here, since I sell a neodymium doped glass
filter, Nonad, as a sideline. Info and low resolution spectra at:

http://www.nezumi.demon.co.uk/nonad/nonad.htm

The didymium filter you used looks to be less dense than Nonad. Was it a
Baader or one of the other possible commercial didymium glasses?

No - it was a sample from an ophthalmatist used, so I understand, in
some prescription glasses

For completeness you might consider also doing one of the standard US
broadband LPRs (optimised for mercury light) and the Orion UK sodium
light filter which is about as good as you can get visually for mixed
HPS and LPS lighting environments. If more people could see independent
assessments of these filters they might buy the right ones.

Agreed. Will be pleased to receive samples including Nonad for
testingg.

If any filter deserves to be called the sodium light buster it is Orion
UKs.

Didymium or neodymium glass like Nonad is only effective against the
nearly monochromatic orange-yellow low pressure sodium lights. Then it
works well, but the effect is still quite subtle visually. Look at the
spectral absorbtion lines and you will see why. It is most effective
photographically when it delays the onset of sky fog and keeps it a more
neutral black for considerably longer exposures in suburban
environments.

I found the spectrum of the near IR leak on TTs R+B a bit confusing at
first, but to be fair to TT you should perhaps give some indication of
how much longer the exposure has to be for that image compared to the
others.

The leak isn't obvious on the normal spectral exposures.
I presume TT R+B is a much longer exposure?

Somewhat longer but not excessively so - the unfiltered sample of
daylight is at the top - the filter only covers the lower half of the
slit in a single exposure. The red leak is at~7000A and an IR block
filter suppresses it and longer wavelengths remembering that some [non
Starlight Xpress - Sony camcorder chips] CCDs typically peak ~7000A.

Another light source that has a very interesting detail spectrum is an
HPS lamp - self absorbed on the sodium D-lines and an odd turquoise
emission line smack bang in the middle of the OIII narrow line filter
passband.

Even the humble low pressure sodium lamp has some other faint spectral
emission lines that should show nicely in your setup.

Yes - I've done LPS [its outside my house!] and will post shortly and
maybe HP sodium too although luckily none are nearby. Just feel a
little conspicuous aiming my devise at street lampsg.

Maurice Gavin

Regards,
--
Martin Brown

Are such glasses widely available?? A pair of them, plus a didymium eyepiece
filter might help solve my local LP Sodium light pollution problem.

Sally
"Maurice Gavin" wrote in message
...
The didymium filter you used looks to be less dense than Nonad. Was it a
Baader or one of the other possible commercial didymium glasses?

No - it was a sample from an ophthalmatist used, so I understand, in
some prescription glasses

Are such glasses widely available?? A pair of them, plus a didymium eyepiece
filter might help solve my local LP Sodium light pollution problem.

Sally
"Maurice Gavin" wrote in message
...
The didymium filter you used looks to be less dense than Nonad. Was it a
Baader or one of the other possible commercial didymium glasses?

No - it was a sample from an ophthalmatist used, so I understand, in
some prescription glasses

(Maurice Gavin) wrote:

HP sodium lamp spectrum is very pretty but deadly for astronomers !!!

"My" street light is a sort of pinky-orange (as opposed to
yellow-orange) Is this HPS? Are there other vapur lamps than LPS and
HPS in common use?

Cheers

Martin

--------------
Martin Frey
N 51 02 E 0 47
--------------

(Maurice Gavin) wrote:

HP sodium lamp spectrum is very pretty but deadly for astronomers !!!

"My" street light is a sort of pinky-orange (as opposed to
yellow-orange) Is this HPS? Are there other vapur lamps than LPS and
HPS in common use?

Cheers

Martin

--------------
Martin Frey
N 51 02 E 0 47
--------------

In message , Martin Frey
writes
(Maurice Gavin) wrote:

HP sodium lamp spectrum is very pretty but deadly for astronomers !!!

"My" street light is a sort of pinky-orange (as opposed to
yellow-orange) Is this HPS? Are there other vapur lamps than LPS and
HPS in common use?

Pink-orange or peachy white is almost certainly HPS. It should strike
initially with the pure orange-yellow of the sodium D-lines and then as
the pressure builds become increasingly whiter upto working pressure.
Some can look pale lemon-yellow depending on type and age of lamp.

Pure nearly monochromatic orange-yellow is characteristic of the sodium
D-line emission of low pressure sodium lamps. They are still the most
energy efficient way of converting electricity into useful visible
light.
They have a bad reputation in the UK because they are seldom (if ever)
shielded. I think I once saw a shielded one on the M60 near Worsely.

Mercury vapour is the other common (but much less efficient) street
lighting technology. All the US branded broadband filters are optimised
for mercury which is still by far the most common lighting over there.
The light has a cold steely blue look and a characteristic spectrum with
very strong lines in the green and purple.

Metal-Hydride gives a whiter light but they are not common as street
lamps. Other technologies exist but are exceedingly rare in practice.

Regards,
--
Martin Brown

In message , Martin Frey
writes
(Maurice Gavin) wrote:

HP sodium lamp spectrum is very pretty but deadly for astronomers !!!

"My" street light is a sort of pinky-orange (as opposed to
yellow-orange) Is this HPS? Are there other vapur lamps than LPS and
HPS in common use?

Pink-orange or peachy white is almost certainly HPS. It should strike
initially with the pure orange-yellow of the sodium D-lines and then as
the pressure builds become increasingly whiter upto working pressure.
Some can look pale lemon-yellow depending on type and age of lamp.

Pure nearly monochromatic orange-yellow is characteristic of the sodium
D-line emission of low pressure sodium lamps. They are still the most
energy efficient way of converting electricity into useful visible
light.
They have a bad reputation in the UK because they are seldom (if ever)
shielded. I think I once saw a shielded one on the M60 near Worsely.

Mercury vapour is the other common (but much less efficient) street
lighting technology. All the US branded broadband filters are optimised
for mercury which is still by far the most common lighting over there.
The light has a cold steely blue look and a characteristic spectrum with
very strong lines in the green and purple.

Metal-Hydride gives a whiter light but they are not common as street
lamps. Other technologies exist but are exceedingly rare in practice.

Regards,
--
Martin Brown

Martin Brown wrote:

In message , Martin Frey

"My" street light is a sort of pinky-orange (as opposed to
yellow-orange) Is this HPS?

Pink-orange or peachy white is almost certainly HPS. It should strike
initially with the pure orange-yellow of the sodium D-lines and then as
the pressure builds become increasingly whiter upto working pressure.
Some can look pale lemon-yellow depending on type and age of lamp.

Pure nearly monochromatic orange-yellow is characteristic of the sodium
D-line emission of low pressure sodium lamps. They are still the most
energy efficient way of converting electricity into useful visible
light.
They have a bad reputation in the UK because they are seldom (if ever)
shielded. I think I once saw a shielded one on the M60 near Worsely.

Mercury vapour is the other common (but much less efficient) street
lighting technology. All the US branded broadband filters are optimised
for mercury which is still by far the most common lighting over there.
The light has a cold steely blue look and a characteristic spectrum with
very strong lines in the green and purple.

Metal-Hydride gives a whiter light but they are not common as street
lamps. Other technologies exist but are exceedingly rare in practice.

Thanks all - no doubts now - thanks to descriptions and spectra.

Cheers

Martin

--------------
Martin Frey
N 51 02 E 0 47
--------------

Martin Brown wrote:

In message , Martin Frey

"My" street light is a sort of pinky-orange (as opposed to
yellow-orange) Is this HPS?

Pink-orange or peachy white is almost certainly HPS. It should strike
initially with the pure orange-yellow of the sodium D-lines and then as
the pressure builds become increasingly whiter upto working pressure.
Some can look pale lemon-yellow depending on type and age of lamp.

Pure nearly monochromatic orange-yellow is characteristic of the sodium
D-line emission of low pressure sodium lamps. They are still the most
energy efficient way of converting electricity into useful visible
light.
They have a bad reputation in the UK because they are seldom (if ever)
shielded. I think I once saw a shielded one on the M60 near Worsely.

Mercury vapour is the other common (but much less efficient) street
lighting technology. All the US branded broadband filters are optimised
for mercury which is still by far the most common lighting over there.
The light has a cold steely blue look and a characteristic spectrum with
very strong lines in the green and purple.

Metal-Hydride gives a whiter light but they are not common as street
lamps. Other technologies exist but are exceedingly rare in practice.

Thanks all - no doubts now - thanks to descriptions and spectra.

Cheers

Martin

--------------
Martin Frey
N 51 02 E 0 47
--------------