What single LED Light source should I use for a microscope? - XHP, MT-G2?

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jcf
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What single LED Light source should I use for a microscope? - XHP, MT-G2?

Hello,
I’ve been searching to mod the existing metal halide lamp (fiber optic) with an LED source. At the moment, the metal halide light travels through a fiber optic cable to the body of the scope. I can use an LED in this fashion – or – more preferably (to limit the amount of light lost to the fibre optic cable), mount the LED source directly to the microscope. There is always the possibility of purchasing an LED light from the manufacturer – however – it’s much more interesting to build your own.

I’m trying to figure out what type of LED I should use to obtain approximatley 2000 lumnious flux (comparable to other LED light sources). I was excited when I was reading about the XHP 70 – however, I’m concerned that the dark cross in the middle of the light will cause a problem.

The light source is travelling through an aperture (hole) of approximatley 8mm, which then travels through a reduction lens approx 60mm away from the source. From there, it enters in the scope and is reflected downwards to the object you are looking at.



Question: What would be the best single LED that would produce 1500-2k Lumen in this scenario? Further questions would be the most appropriate driver and potentiometer for this LED.

Thanks!

John

Edited by: jcf on 03/29/2015 - 16:08
djozz
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Hi jcf, answering this question this may need a basic drawing of the light source, lens, coupling to the fiber. Could you make one (just ball-pen on paper will be fine). The main question is if the light source is (close to) imaged on the specimen, usually in microscope lighting it is not, and in that case the black cross will not be there.

Welcome to BLF, btw! Smile

jcf
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Hi djozz,

Thanks for the points. I have included a basic diagram from the internet – I don’t have exact measurements yet (scope its at work).

However, from the objective lens to the object, it is 250mm. I’m estimating that the distance from the object to the mirror that reflects it downward would be 350mm total.


Thanks

JCF

Firelight2
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My guess is an XHP70 or MTG2 are too bright. Those LEDs produce light output equivalent to a bright halogen bulb. You can light up a football field with them.

My guess is you’d be better off with something like a Nichia 219B. Probably sufficient light and it’s high CRI so should give better color rendition.

Photons Away
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Might you be using the microscope for other than biological work? I know for biological work colour rendition is crucial in certain cases.

One more thing to keep in mind is whether you are using a darkfield or grayfield (setting) or scope. If the LED is custom mounted the light from it will need to be completely masked or deflected so as to not light the surrounding areas or background.

Best wishes

jcf
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PhotosAway – Thank you for your response.

Indeed, the work is biological work – color rendition is important to some degree, however, the degree of illumination is more important, as I’m trying to see deep into the root canals of teeth (cat is out of the bag!). Often, 6500k is the color that is used – probably more due the availability of light sources with high intensity rather than color. (however, I could be wrong). I would prefer a little warmer light.

Today’s 1st test: I used a small headlamp the kids had laying around the house (defiant from Home depot) – I’m assuming it’s maybe 3 watts……I placed it onto the body of the scope and then compared it to the transmitting it through the fibre optic cable (which is how the metal halide light is transmitted). The light was pretty weak – as was my iphone light – albeit – it was expected and I needed a baseline. Interestingly, the light was more intense when I used the reflector into the fibre optic cable. I’m assuming that it allowed capturing of all the light into the cable versus lost to the environment.

Second Test:

As a test, I used a portable medical headlight that has been advertised to produce 7000 foot candles (I’m not sure why they use this measurement) @ 6500k. I transmitted the light through a fiber optic cable, then into the microscope. The cable actually provided a brighter light than simply placing the LED light to the light port on the body of the scope. The light image on the paper is the LED direct from the head source (not through the scope).

The light was approximately at 50% of the brightness that I need (and can get through my existing metal halide). I’m not sure at the moment what type or model of LED is in this light, as that will be a well kept secret. http://www.orascoptic.com/products/headlights/discovery.

Thanks all for your advice! It is greatly appreciated.

John