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 Post subject: Gemolite V LED replacement darkfield lamp
PostPosted: Thu Nov 29, 2018 4:51 am 
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I recently snagged a Gemolite V base to go with my AO 0.7-4.2X head. The diaphragm was broken and it needed a new stone holder, but I bought a replacement stone holder and located a replacement iris diaphragm on ebay, so I will soon be good to go. This model uses an incandescent lamp with a bayonet base. Looking at replacement LED bulbs, I see several small bulbs in the 40 to 60 watt range in daylight temperature (5K to 6K) that look like they will fit. My main interest is colored stones and I wonder if anyone has found that an LED bulb is a suitable replacement for this base. I know that LED output has improved a lot over the years, but I couldn't find any current discussion of these types of possible replacements here.

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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Thu Nov 29, 2018 12:35 pm 
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It is a good question I have been pondering recently as well. There is some info on LED conversions on venues like the photomacrography and microbehunter forums, but mostly more custom creations rather than dropin replacements. LEDs have come a long way since the bulk of the discussion that happened here back in the day.
Probably worth a try, anyway.

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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Thu Nov 29, 2018 3:07 pm 
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Needing a two post bayonet bulb base narrows the field a little...I did find some replacements that would boost the wattage a little and give me daylight white color (5K to 6K) but the CRI was in the 80's and I'd like better...it seems the higher CRI bulbs were warm white. Perhaps it wouldn't be too difficult to retrofit a different base, which might lead to more options, so I'll have to look at bulbs with other bases, and, if I find something great, I'll look at changing out the base.

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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Thu Nov 29, 2018 4:41 pm 
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These days LED bulbs are continuous spectrum, depending on the model the output may be a little down in the violet, but I wouldn't have thought it a problem. As for the difference in bases, I wouldn't have thought that any competent metal worker would have any difficulty in making an adaptor so a modern bulb can be used in the old incandescent fitting. I certainly wouldn't.


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Fri Nov 30, 2018 3:54 pm 
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Alan F. wrote:
These days LED bulbs are continuous spectrum, depending on the model the output may be a little down in the violet, but I wouldn't have thought it a problem.


Incandescent lamps are (were?) a bit down in the violet too. Anyways, LEDs have indeed come a long way, and pretty much replicate incandescence. Just went through my mother-in-law's house replacing horrid CFLs with LEDs... so much better.


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Fri Nov 30, 2018 10:26 pm 
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They have made the warm white LEDs have a pretty high CRI. So in that respect they are similar to the halogen and regular tungsten bulbs that were on the Gemolite in the first place.

However be aware that there is a LOT of lie ing in the published spectra of LEDs They ALL have a peak in the blue because they are fluorescents. They just don't have the mercury lines that fluorescent tubes do. But there is a lot of mumbo jumbo and hoodoo in cri measurements. The hardest part was actually getting the red right not the violet. A lot of the so called warm white "natural" lights have extra red emitters.

In the higher color temperatures they are also getting better but still not suitable for matching colored stones. They are not as good as real daylight or xenon arc lamps. Especially not if someone other than the manufacturer measures the spectrum.

Do let us know what you find after shopping and give us links. Also whatever you get, take a look at it through your hand spectroscope.


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Sat Dec 01, 2018 3:32 am 
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Thanks for your cautions, Gene. As I noted in my first post, I'm waiting for the replacement diaphragm to wend its way here from China before putting the scope back together. At that point it will be easy to try out some replacement bayonet base LED bulbs and compare them with the original incandescent tungsten lamp.

Actually, when I think about it, any color grading would probably be done with the overhead light, while the transmitted light/darkfield bulb would be used more for looking at inclusions, so perhaps the CRI and color temperature are less important than I originally thought. The boost in wattage with the cooler operating temperature may be the real benefits to making a change. It would also be possible to have a dim-able bulb, which would be a convenient upgrade that wasn't available on the original Gemolite Mark V. I'll post again when I have something to report. Thanks for all the feedback.

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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Sat Dec 01, 2018 8:58 am 
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Gene, can I recommend that you read up on LED's for they are certainly not fluorescent lamps?


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Sat Dec 01, 2018 3:05 pm 
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White LEDs are indeed fluorescent lamps. They are a square of a YAG based fluor which is deposited over a blue LED. The blue LED takes the place of the low pressure mercury arc in the tube type fluorescent.
This explains the peak at 460 nm that they can't get rid of. (just as in high cri fluorescents they can't eliminate the mercury lines) The compounding of fluorescent powders ,for these purposes, was already very advanced from the fluorescent light industry by the time the LED came on the scene.

I once sold a microscope to an engineer in Chicago and delivered it. He was an LED engineer and had obtained some of the raw fluorescent powder (all from Japanese hi tech companies) which we had a lot of fun playing with. They were all rare earth doped YAG powders very finely ground. He had multiple types with different colors. They were incredibly efficient. And some of them amazingly phosphorescent. It was a real geek fest. I don't think he had many visitors to his basement lab that appreciated such things.
He also had the first COB LEDs I had ever seen (large area Chip On Board) I think he was designing traffic lights and the yellow one looked like a potential sodium lamp substitute. This was long enough ago that there weren't white LEDs yet.

There are also RGB based white LEDs but these (so far)never have the high cri that the fluorescent ones claim to have.


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Sat Dec 01, 2018 4:11 pm 
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So the LED is fluorescent in that it puts out discrete quanta of light at single wavelengths? I don't understand how the spectrum can be continuous if this is the mechanism, but perhaps you can tell me.

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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Sat Dec 01, 2018 5:44 pm 
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It does not put out single line wavelengths anymore than high cri fluorescent tube or cfls. Many of these have very continous spectra but in the case of fluorescents and expensive cfls they still have the mercury lines quite visible both in the visible band and in the UV.

Another interesting fact is that the smoother and better quality the spectrum the less efficient the fluors are. Lamps that were sold for "natural light" and bathroom or kitchen use have much lower efficiencies than regular Daylight which are less than Cool White. The most efficient were the cfls which had almost entirely line spectra which is why the light from them has a ghastly unreal quality. Most of the energy consists of four or five very line type peaks in relatively pure color.

The fluorescent material doesn't really care what the original energy source is other than shorter wavelength is higher energy. There are TONS of pages online on these subjects which can explain them much better than I can. The companies that were in the business of selling lightbulbs used to publish endless technical specifications on each type of lamp. I have to say they don't bother as much any more. Perhaps to give fewer clues to copycats.


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Sat Dec 01, 2018 5:56 pm 
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Quote:
Applications of fluorescence
Lighting
Further information: Fluorescent lamp

The common fluorescent lamp relies on fluorescence. Inside the glass tube is a partial vacuum and a small amount of mercury. An electric discharge in the tube causes the mercury atoms to emit mostly ultraviolet light. The tube is lined with a coating of a fluorescent material, called the phosphor, which absorbs the ultraviolet and re-emits visible light. Fluorescent lighting is more energy-efficient than incandescent lighting elements. However, the uneven spectrum of traditional fluorescent lamps may cause certain colors to appear different than when illuminated by incandescent light or daylight. The mercury vapor emission spectrum is dominated by a short-wave UV line at 254 nm (which provides most of the energy to the phosphors), accompanied by visible light emission at 436 nm (blue), 546 nm (green) and 579 nm (yellow-orange). These three lines can be observed superimposed on the white continuum using a hand spectroscope, for light emitted by the usual white fluorescent tubes. These same visible lines, accompanied by the emission lines of trivalent europium and trivalent terbium, and further accompanied by the emission continuum of divalent europium in the blue region, comprise the more discontinuous light emission of the modern trichromatic phosphor systems used in many compact fluorescent lamp and traditional lamps where better color rendition is a goal.[51]

Fluorescent lights were first available to the public at the 1939 New York World's Fair. Improvements since then have largely been better phosphors, longer life, and more consistent internal discharge, and easier-to-use shapes (such as compact fluorescent lamps). Some high-intensity discharge (HID) lamps couple their even-greater electrical efficiency with phosphor enhancement for better color rendition.[citation needed]

White light-emitting diodes (LEDs) became available in the mid-1990s as LED lamps, in which blue light emitted from the semiconductor strikes phosphors deposited on the tiny chip. The combination of the blue light that continues through the phosphor and the green to red fluorescence from the phosphors produces a net emission of white light.[citation needed]


from wikipedia "Fluorescence"


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Wed Jul 28, 2021 5:40 pm 
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This is an old thread, but perhaps of some interest to some owners of old Gemolite scopes. I didn't replace my incandescent lamp until it blew out a few days ago. A search on Amazon yielded this best price alternative:

<<Lamsky BA15D LED Double Contact Bayonet Base Sewing Machine Bulb AC110-130V,T3/T4/C7/S6,4W Daylight 6000K,LED 40W Halogen Replacement Bulb,No-Dimmable,2-Pack>>
Price was $9.48 with the tax and now I have one and a spare!

The replacement bulb seems brighter and, of course, is a daylight color temperature rather than the warm incandescent one of the former bulb. This is pretty close to the 6200K or higher fluorescents recommended by the Gemworld Guide. While not quite the point source approximation of the filament of the incandescent, the rows of LEDs seemed to give pretty good darkfield lighting. I haven't done any tests to see whether there will be any color anomalies due to spectral peaks, but the color rendering seemed OK. I only used the lamp for a few minutes, but there wasn't any heat at all and I assume that will be the way it operates long term. Bulb was a little hard for my 74 year old hands to push in and turn, but finally got it in after a couple of attempts. Seems the bumps on the bottom might be a little higher than those on the old lamp.

I hadn't used the Gemolite much lately and got it out recently to look at a parcel of cut stones I received. Then used it for examining some rough I will be cutting. I'd forgotten how wonderful it is to see well into stones! I don't see any downside to replacing the old incandescent bulbs unless you are just in love with the old warm glow. I did see incandescents available, too, so you can have it either way.

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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Thu Jul 29, 2021 12:46 pm 
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Thanks RoyJohn for that insight and suggestion. =D>


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 Post subject: Re: Gemolite V LED replacement darkfield lamp
PostPosted: Sun Apr 17, 2022 9:44 am 
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Thanks for the LED bulb replacement suggestion. I sometimes use a gemolite to examine plankton tow material in dark field and the original bulb fries the samples pretty quickly. Amazon also lists a warm white option for this bulb; does anyone know whether the daylight or warm white would be better for general gemolite use? Thank you!


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