LED Light & Spectroscope

ROM · **Posted:** Mon Oct 30, 2006 1:08 pm

Hi Everyone,

I'm trying to come up with a really small and portable means of using a spectroscope at gem shows. The arrangement I presently have in mind involves a small LED pocket keychain light. But I'm not sure of the spectral components of that kind of light. I seem to be picking up a rather prominent absorption band in the blue but I'm not really sure. It's one of those "I think I see it sometimes" deals.

Can anyone else compare observations with me? I've been looking at what I think is malaia garnet with it and I'm finding manganese bands in the blue where they should be. But are they from the stone or the LED?

Rick Martin

Doos · **Joined:** Sun Oct 16, 2005 12:42 pm **Posts:** 2591

Hi,

Test the led in the toilet (lights out) .. if there still is absorption in the blue it is not really monochromatic.

jleb · **Posted:** Mon Oct 30, 2006 11:38 pm

I use one of those cheap incandescent bulbed penlights that have the full spectrum. I got it at kent's tools for $3.00. Works great, full spectrum..

ROM · **Posted:** Tue Oct 31, 2006 12:14 am

jleb, any chance you have a stock number? I checked the site but don't find it listed. I'd like to order one and check it against what I have. Thanks,

Rick Martin

jleb · **Posted:** Tue Oct 31, 2006 12:38 am

call this number and ask for Kent 520) 624-8098

Tell him you want the little white penlight with the clip switch.. I got 3 ( backups)...

t6b9p · **Posted:** Tue Oct 31, 2006 1:03 am

If you are using a white LED then it is going to have a strong broad blue component. You may also find that it is a little weak at the red end.

JB · **Joined:** Tue Nov 29, 2005 2:02 pm **Posts:** 2647

Rom and all,
I received a small white light LED clip-on booklight for Christmas. After checking with the spectroscope, I can verify your observations.
There was strong absorption in the lower end of the blue right into the green with weaker adjacent absorption in the blue that was hard to determine if it was a band or a series of lines. The blue area was rather broad and narrow in the violet.
I would a carefully check any light source you are considering using for spectroscopy for any type of emission or absorbtion lines.

JB · **Joined:** Tue Nov 29, 2005 2:02 pm **Posts:** 2647

Interesting site on lighting and spectroscope.

http://ioannis.virtualcomposer2000.com/ ... olorphotos

ROM · **Posted:** Sat Jan 06, 2007 11:25 am

JB wrote:

Rom and all,
I received a small white light LED clip-on booklight for Christmas. After checking with the spectroscope, I can verify your observations.
There was strong absorption in the lower end of the blue right into the green with weaker adjacent absorption in the blue that was hard to determine if it was a band or a series of lines. The blue area was rather broad and narrow in the violet.

Thanks for the input JB. Since I posted I've been able to confirm the same thing and have adopted a filament light strategy.

Rick

ROM · **Posted:** Tue Jan 09, 2007 1:28 pm

JB and Everyone,
There's a very interesting article by Bear Williams about ultraviolet/led lights in the current "Gem Market News." It discusses how many UV lights available today may give misleading or inaccurate results in gem ID and how led technology may provide better answers. It also provides graphs showing how various led lights perform spectroscopically.

I found the article very interesting and thought-provoking but my faith was shaken a little when Williams mentioned "malaya" and tsavorite garnets as "species." Oh well, you can't expect perfection!

Rick Martin

jleb · **Posted:** Tue Jan 09, 2007 4:10 pm

can you give us a link?

ROM · **Posted:** Tue Jan 09, 2007 4:16 pm

Sorry, I don't think there is one. It's published by The GemGuide and as far as I know exists in print form only. PM me.

Rick

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