A hydrogen spectrum tube-- for fun and etalon testing

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A hydrogen spectrum tube-- for fun and etalon testing

Post by thesmiths »

I've recently gotten hold of a few common spectral sources to do spectroscopy experiments -- a low pressure sodium lamp, a neon tube and most recently a hydrogen tube. These are nice tools for spectrometer calibration and testing and they are fun to play with as well. The light they produce is quite dramatic. I can share here some experience putting these to use.

To start with, I got an 18W low pressure sodium lamp from eBay (for 23 pounds). The Philips SOX-E 18W comes with a BY22D socket. The datasheet says that the nominal lamp current is 0.33A at an operating voltage of 57V. There is a lot of conflicting information how to drive these bulbs. I decided to go with the traditional approach of using a wire-wound ballast (a choke or inductor) which compensates for the negative resistance of the sodium lamp. The ballast I used was a "sunbed fluorescent lamp tube lighting ballast choke 15/25 Watt 230V 50Hz" purchased used from eBay. The labelling on the choke said "25W 0.29A" and "15W 0.31A" which seemed close to the nominal current of 0.33A mentioned in the SOX-E 18W datasheet. I also ordered a SOX ignitor; the one I found was a "Parmar PB035K245 ignitor for 35W SOX low pressure sodium bulb" purchased as new from eBay. The choke and the ignitor had wiring schematics on them which were very helpful. One wire of the choke is connected to the live 220V line and the other end to a terminal of the sodium lamp. The other terminal of the lamp is connected to the neutral 220V line. The ignitor goes across the two inputs of the sodium lamp. The BY22D socket is meant to be used with a ceramic base but since an 18W bulb should not get very hot, I guessed that a normal B22 bayonet socket base would probably work. It turned out to fit perfectly and did not have any heating issues. I bought a "B22 lamp holder with switched cable & fitted plug" from Amazon and used the mains plug and switch to drive the ballast and the B22 lamp holder for the sodium bulb.

Below is a photo of the low pressure sodium tube, along with the drive electronics. It produces a very pleasing warm light.
sodium setup
sodium setup
383.jpg (180.74 KiB) Viewed 2585 times
And here are images of the spectrum from the tube: first with a short exposure that shows the sodium doublet (also seen in solar spectra) and the second is with a longer exposure that shows additional lines from the neon/argon mixture that is used to initially heat the sodium metal when the lamp is first turned on.
sodium doublet
sodium doublet
4015.jpg (125.58 KiB) Viewed 2585 times
sodium spectrum
sodium spectrum
4007.jpg (147.21 KiB) Viewed 2585 times
Next up is a 190mm neon spectral tube, purchased from a specialist seller on eBay (for 15 pounds). The drive electronics for this is very easy to get hold of. I used a 3kV, 30mA electronic neon sign transformer, available quite cheaply from Amazon. Below is a photo of the neon tube mounted in front of one of our home-built spectrometers. Neon light has a very nostalgic feel to it. It is actually much redder than the photo shows.
neon setup
neon setup
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Here is an image of the neon spectrum which shows a very large number of closely spaced lines:
neon spectrum
neon spectrum
3936.jpg (268.84 KiB) Viewed 2585 times
Most recently, we bought a 260mm hydrogen spectrum tube from eBay (for 18 pounds). The tube itself is not very expensive but the drive electronics is (usually at least 150 pounds). After looking into various options and consulting with a few experts, I decided to use the neon transformer. The disadvantage/advantage is that it provides more current than is typically used to power these tubes but the high current does provide more light. I measured about 20W of electrical consumption with the hydrogen tube at the input of the transformer (vs around 10W for the neon tube). The instructions for the tube says "The tube is intended for intermittent use only and is not to be used as a lamp source. It should be used for periods of 30 seconds on / 30 seconds off. The useful life will be reduced if the tube is not used as recommended or allowed to overheat." I try to stick by the 30 second rule quite carefully, especially since I am probably running it hotter than intended.

Below is a photo of the tube connected to the neon transformer, both with the current off and on. Hydrogen has a very dramatic purple colour.
hydrogen off
hydrogen off
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hydrogen on
hydrogen on
404.jpg (278.78 KiB) Viewed 2585 times
Since the tube is quite delicate, I built a frame to hold the tube out of foam board (and a hot glue gun) which is open on the sides for direct viewing and has a diffusion screen on one of the foam board sides:
hydrogen mounted
hydrogen mounted
435.jpg (250.36 KiB) Viewed 2585 times
Below is a photo of the tube through Baader hydrogen alpha and hydrogen beta filters:
hydrogen filters
hydrogen filters
436.jpg (269.46 KiB) Viewed 2585 times
Finally, here a spectrum of the tube which shows the hydrogen alpha, beta and gamma lines, along with one faint stray line (possibly sodium from the glass?):
hydrogen spectrum
hydrogen spectrum
4041.jpg (129.87 KiB) Viewed 2585 times


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by rsfoto »

Hi,

Very interesting :bow2


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by DeepSolar64 »

This is really cool and familiar to me. I work at the GE Current lighting plant in Hendersonville NC. At one time we built HID lighting fixtures for indoor and outdoor lighting applications. I worked for quite a number of years building coil wound ballasts, glassing reflectors and casting housings for the fixtures. I worked also assembling them for a couple of years. I started there back in 1994 and we have went from HID fixtures, High Pressure Sodium, Mercury, Metal Halide and later induction lighting to now where we do exclusively LED lighting. I now work in SMT where we assemble the PCBAs for the fixtures. We do have labs which work with the spectroscopy, lumens, CCT and other characteristics of the lights. I have never had the pleasure of working in there though we do measure color temperature as a part of testing our assemblies in SMT.

I do sometimes feel like an astronomical hypocrite though. What we produce has the ability and is, along with other manufacturers contributing significantly to the light pollution that is destroying the night skies. Thankfully solar is immune!!

I may end up getting into spectroscopy. I find the study of light itself very fascinating. I may first buy a simple spectroscope. I have looked at several. I would also like to have a CCT light meter. With these I could analyze light from different sources like common man made light sources and natural ones like the sun, stars and planets. So much can be learned from light itself.

Thanks for posting this. It's a BIG thumbs up from me!

We have never done LPS, at least since I have worked for GE Current. It is said to be the most sky friendly of all the outdoor light sources. It's more like a fluorescent lamp than it is to it's HID cousin the HPS sodium lamp.

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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by thesmiths »

To James: yes, low pressure sodium (LPS) is by far the most astronomy friendly light source. As you can see from the spectrum, almost all the light is concentrated in the sodium doublet. They used to be quite common in Europe (I don't think they were used too much in the US). First they were replaced by high pressure sodium, which has many more spectral lines, and now LEDs (which are completely broadband). I think they are still used near major telescopes. They take about 10 minutes to warm up fully. I made a time lapse of this (set to some relaxing music) which you can see here; towards the end, there is some spectroscopy.

I believe Philips was the last manufacturer of LPS and stopped production as few years ago. They are truly vintage now. They are fantastic light sources for spectrum calibration -- very bright with well defined doublet structure. I like the old school wire-wound ballasts, by the way (although they do dissipate a lot more energy than the high-frequency electronic ones).


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by DeepSolar64 »

Yes, I had read many years ago that LPS was the best outdoor light for reduction of light pollution. The narrow doublet of light was easily filtered out at the telescope. It's sad that it now has largely fell away to the wayside. I asked an engineer at GE years ago about LPS and he had never heard of them ever being made at the Hendersonville plant.

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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by Carbon60 »

Very interesting. Thank you.
I remember the old street lights that came on with a pinkish glow before becoming bright yellow some minutes later.

Are you using these light sources to calibrate your spectrometer and do you use RSpec? https://www.rspec-astro.com/

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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by marktownley »

Very interesting indeed, thanks!


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by christian viladrich »

Well done !
I have just tested two etalons with a Ha lamp : a Coronado SM III 60 mm and a SM III 60 mm RichView.
From the measurements, we are now able to derive the FSR, FWHM and delta CWL compared to Ha line. The results are quite interesting.
I'll try to post a link to a webpage this WE.


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by thesmiths »

I had always seen the potential utility for having a hydrogen source but was deterred by the high cost (around $200 for the tube plus the power supply). But the cost of the tube alone is only around $20 and a neon power supply is less than $15. This makes the cost/benefit more sensible. By the way, the failure mode for running them too long / too hot appears to be reaction with the electrodes at the ends (typically made of aluminium). The electrodes will react with hydrogen, which eventually drops the pressure in the tube and makes them unable to light. This does not happen with neon, of course.


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by thesmiths »

To Stu: yes, I have used RSpec. Do you find this is the best program to use for spectroscopy tasks?
Here, for example, is a high resolution image of the sodium doublet. This was actually not done with the sodium lamp but rather the old fashioned way, burning salt with a butane kitchen torch (apparently they are useful for making crème brulee). The kitchen method has some obvious disadvantages (not very reproducible and rather quick reflexes required), which was the motivation to build the low pressure sodium lamp. I have rotated it by 90 degrees to better fit on the page.
sodium lines
sodium lines
3822 - Copy.jpg (73.15 KiB) Viewed 2530 times
This was taken with a 1800 line/mm grating and a 5 micron slit. The narrow dark line is presumably from self-absorption. Hot sodium vapour provides a somewhat diffuse luminous spectrum (from doppler effects, among other things) while cooler sodium vapour creates a narrow absorption line in the centre of the broad luminous line (somewhat analogous to the Fraunhofer mechanism). I have seen this effect in the low pressure sodium lamp as well; presumably there are significant temperature inhomogeneities in those also. The RSpec trace is shown below.
doublet rspec
doublet rspec
sodium doublet.JPG (87.97 KiB) Viewed 2530 times
Apparently, the ability to see the self-absorption line (which in the old days was called a "reversal"), is a sign that the spectrometer is working with quite high resolution. But burning salt is not the most controlled process so the self-absorption is sometimes stronger, sometimes weaker. The low pressure sodium lamp obviously provides a more consistent output.


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by thesmiths »

Finally, some photos of a PST etalon in front of the hydrogen tube. First, with no filter in front of the tube (only a diffusion screen, obtained from an old 35mm slide copier):
full spectrum
full spectrum
4199.jpg (264.73 KiB) Viewed 2499 times
In this case, both the hydrogen alpha and beta light is sent into the etalon. The etalon surfaces are obviously optimised for reflectivity of H-alpha so the red lines are quite sharp, indicating fairly high finesse. As finesse is related to reflectivity of the etalon mirrors, the blue H-beta interference fringes are quite broad. Now, with a H-alpha filter between the tube and the etalon, the image looks more familiar:
h-alpha
h-alpha
4212.jpg (185.35 KiB) Viewed 2499 times
The fringes are quite sharp and well formed. It's possibly tuned a little more off than optimal (although I am not an expert at interpreting this). Most likely, a dark red photographic filter is sufficient to filter out the H-beta light and provide a good source for etalon evaluation, which would be both larger and more cost effective than an astronomical filter.


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by thesmiths »

As another improvement to the hydrogen spectral tube to make it more etalon friendly, I attached some Rubylith plastic film on the inside of the foamboard underneath the diffusion screen. Rubylith, which is often used in darkrooms, etc, has about the same transmission as a 25A red photographic filter. But of course you can get it in large sizes and cut it easily with scissors. Using a handheld spectroscope, I verified that the Rubylith blocked out the blue hydrogen beta light. I also put some on one of the sides to take a photo to compare with the bare hydrogen tube.
with rubylith
with rubylith
470.jpg (123.37 KiB) Viewed 2488 times
bare tube
bare tube
435.jpg (250.36 KiB) Viewed 2488 times
I think this reproduces the kind of hydrogen alpha light sources I have seen used at manufacturers like Lunt as diagnostic tools. For examining larger etalons, I could imagine putting a few hydrogen tubes parallel to one another to get a more even light source (as was typically done with florescent tubes in the old fashioned slide sorters). A single neon transformer would be able to drive quite a few hydrogen tubes in parallel.


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by Bob Yoesle »

For examining larger etalons, I could imagine putting a few hydrogen tubes parallel to one another to get a more even light source (as was typically done with florescent tubes in the old fashioned slide sorters). A single neon transformer would be able to drive quite a few hydrogen tubes in parallel.
Seems like an excellent suggestion! Thanks for posting.


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by christian viladrich »

The rubylith is an excellent idea. I use an old W25 filter screwed on the camera lens when needed.


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by EGRAY_OBSERVATORY »

I have been following these well-interesting posts and images and quite fascinating - thanks vm.

So now I have a project to start (after completing others in the pipe-line first), as I have a number of street-lighting Sodium lamps, fitments and a complete street-lamp head. That was used for necessary steam-cleaning of our Shorts Belfast aircraft and their very large and enclosed under-carriage bays.

The steam would reduce the inspection-visibility whilst cleaning to zero without the aid of the sealed Sodium street-lamp mounted on a tripod for the purpose and the company I worked for - found this an excellent idea to clean the bays quickly - before engineers did any work to complete...

Powerful Halogen work-lights were simply not suitable as to bright and the steam would reflect that light - far too much as well as the Mercury one as below... Also the heat of the glazed Halogen glass-cover would shatter with the wet-steam too !!! (the plastic covered Sodium and Mercury units did not suffer from that problem...

I also have a Mercury street-lamp too, which was not suitable after trials for the under-carriage bays, but retained by me to date, so as all these were supplied to me F.O.C. by a friend in the trade of replacing street-lighting, I might as well make use of those for some similar experiments.

Just need a decent Spectroscope and time in the future...

Cheers
Terry


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by EGRAY_OBSERVATORY »

Hello,
As this is an interesting subject and especially as I have a Solar interest in imaging, perhaps with my existing Sodium and Mercury assets, perhaps you could advise if the items in the web-links below (available from my own normal suppliers) will be the best to utilise for some future projects ??

https://www.rapidonline.com/eisco-ph100 ... it-52-3382
and
https://www.rapidonline.com/eisco-ph061 ... mm-52-3340

To get either or both is no problem and any pre-advice welcome.

Thanks vm
Terry


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by marktownley »

Rather interesting if I do say!


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by EGRAY_OBSERVATORY »

Yes is very interesting. Any answers to my previous would be useful to me please

" Hello,
As this is an interesting subject and especially as I have a Solar interest in imaging, perhaps with my existing Sodium and Mercury assets, perhaps you could advise if the items in the web-links below (available from my own normal suppliers) will be the best to utilise for some future projects ??

https://www.rapidonline.com/eisco-ph100 ... it-52-3382
and
https://www.rapidonline.com/eisco-ph061 ... mm-52-3340

To get either or both is no problem and any pre-advice welcome. "

Thanks vm
Terry


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by thesmiths »

To Terry: I'm not quite sure what the first item is; it is not well described in the listing. The second item is a quite standard spectrometer. It will be rather big and heavy. I actually bought a similar one many years ago used on eBay to learn about spectroscopy but it was only useful at the beginning.

The best spectroscope to start with is the https://www.patonhawksley.com/product-p ... ectroscope. They are sold via many distributors but I believe they are all made by Paton Hawksley. I still use this one very often as it is so convenient to use to get a quick idea of a spectrum. However, it is almost impossible to take a photo of the spectrum you see.

A good astronomy tool is the Star Analyser https://www.patonhawksley.com/product-p ... r-analyser. You can attach this to a camera and take some interesting spectrum photos of light sources and stars.

I also bought the "grism" and "slit" used in the "Paton Hawksley Benchtop Spectroscope" and built a home made spectroscope that I still use. This requires some additional optics but it allows taking nice photos of spectra very quickly. I attach some photos of this one because it is not hard to build and is quite flexible.
grism dslr
grism dslr
grism-complete.jpg (121.46 KiB) Viewed 2411 times
grism back
grism back
grism-back.jpg (54.17 KiB) Viewed 2411 times
grism front
grism front
grism-front.jpg (66.56 KiB) Viewed 2411 times
solar spectrum
solar spectrum
solar-spectrum.jpg (32.32 KiB) Viewed 2411 times
The first camera lens is placed backwards so that its focal point is focused on the slit and therefore creates a collimated beam that illuminates the grism. The angled side of the grism faces the slit and the flat side faces the camera (the angled side has a diffraction grating on it). The camera side lens is focused at infinity. When the collimator lens is focused correctly, the lines created by the slit will be sharp at the camera.

If you use a monochrome camera, you can get higher quality results than with a DSLR but it is much less convenient. Here is a complete solar spectrum taken with the grism and a large monochrome astronomy camera:
solar lines
solar lines
spectra_013_disp.jpg (156.81 KiB) Viewed 2411 times


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by EGRAY_OBSERVATORY »

Thank you very much for the interesting answers of which I will follow-up and make decisions as to what to acquire.

I have previously done a little research with a CD in a small tube, with fascinating results and reading the posts is enthusing me to do some more research. I also have some prisms which have also resulted in some interesting results, so worth investing in something better to continue with...

I also have a camera similar to the one shown as my Panasonic DMC-G2 etc., so along with my engineering-skills should be able to venture into the subject - quite well... ps I've even got the same green cutting board as in your images...

I did realise that the eisco-ph0619- was a tad large and no doubt heavy, so will on your advice give that a miss and look more at the https://www.patonhawksley.com/product-p ... ectroscope etc.

Once again thanks vm for the advice and hopefully in the future will be able to post some results here.

Best Wishes
Terry


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Re: A hydrogen spectrum tube-- for fun and etalon testing

Post by Merlin66 »

Paul’s 3D printed LowSpec instrument is giving very good performance and is very cost effective.
https://www.thingiverse.com/thing:2455390
Well supported on the https://groups.io/g/astronomicalspectroscopy

Many of us use BASS Project for Spectral processing. It has a comprehensive manual and well supported.
https://groups.io/g/BassSpectro

Remember if you build/buy a spectrograph it can also be used with a suitable scope as a spectroheliograph (SHG). Then you can safely image the solar disk at any wavelength CaK, Mg, Fe, Na, any of the hydrogen Balmer lines etc. etc.
Fulvio's good eBook on his SHGs is worth reading.
English version here:
http://www.lightfrominfinity.org/Libro% ... graphy.pdf

There are further details on the https://groups.io/g/astronomicalspectroscopy


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