Latest recommendation for single die LED for microscope

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Andy Davies
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Latest recommendation for single die LED for microscope

Post by Andy Davies »

Any ideas for latest recommendation for single die LED for microscope?

High power, good CRI, colour temp 4000-5500K and as even a spectrum as possible.
Last edited by Andy Davies on Tue May 12, 2020 3:14 pm, edited 1 time in total.

Macro_Cosmos
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Post by Macro_Cosmos »

You need to define what high power and high CRI is.
Generally, the higher the power, the worse the CRI.

To me, anything with a CRI below 97% is considered "yawn... next one", I might be extreme, however some draw the line at 99% and some draw it at 90% which IMO is low CRI. Just imagine losing 10% of your savings...

Most LEDs, even the so called high CRI ones, have a massive spike in the blue spectrum, and then it drops, and becomes steady. So asking for the spectrum graph is always a good idea.

Andy Davies
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Post by Andy Davies »

Yes, high CRI doesn't mean a colour spectrum that matches daylight.

What are you using?

Charles Krebs
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Post by Charles Krebs »

If you are looking for a "single die" to replace a tungsten bulb filament, you might need to compromise your spec list. If you could figure out how to use a COB of about 10mm diameter you have some very interesting choices.

You asked about single die...
Cree XP-G2. (5700k, 90CRI, ~6W)

CreeXM-L2 (3000k, for the 90CRI. But about 9W. Higher cct available but with lower cri.

Cree XHP70.2. This is not a single die, but 4 packed into a square tightly enough that it might work for a bulb replacement for Koehler. 5000k, 90cri. ~27W. This puppy really cranks out the light!

Cree XHP 50.2. same as above but smaller, ~ 18W


If you could live with a 10mm diameter COB you should look at Yuji. 9W, 5600k, 98 cri. Although it is "self-serving" check out their website for some very good info on high CRI leds. (At this page: https://www.yujiintl.com/high-cri-led-lighting.html )

Bridgelux Decor Ultra Vero 10 (also available in larger diameter/power). 9-12W, 3000k, 97cri.

Except for the XHP50,2 I've used all of the above in one way or another. All very good. One potential issue with the Cree LEDs. If you "collect" light at a large angle away from the center, Cree LEDs color tend to shift to a more yellow light. So this could be a problem with some illumination set-ups.

Andy Davies
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Post by Andy Davies »

Yes, single die Charles. I've used a variety of CREE LEDs and just wondered if anyone had discovered and tested any of the latest ones.

Charles Krebs
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Post by Charles Krebs »

Andy,
just wondered if anyone had discovered and tested any of the latest ones.
Did you have a model in mind. The one's I mentioned were from memory, but we ran a series of tests on quite a few other Cree, (as well as a few Luxeons) relatively recently. I can't access the results until the current "lockdown" ends at the end of the month. At the time we were more interested in how much power we could "pulse" them before killing them, so I have some output numbers (continuous and pulsed) but not much on CRI or color rendition other than the spec sheets.

As you are aware, very high CRI along with high power output are not easy to find in a single die LED.

I'm curious what LEDs Macro_Cosmos is referring to. I've never seen a single die (that had a "usable" power output) at the CRI ratings he mentioned.

vitikin
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Post by vitikin »

I have used the XHP70 (12V) very successfully as a bulb replacement for a goose neck light source. It needs lots of heat dissipation but with a 4sq in heat sink it works nicely.
The idea of using it as light bulb replacement for a Zeiss Standard Fluorescense microscope attachment light source is interesting if it works. I think I can make it physically fit and get enough heat to dissipate.
Would the light characteristics of this chip work for the application?

Chris S.
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Post by Chris S. »

Charles Krebs wrote:If you could live with a 10mm diameter COB you should look at Yuji. 9W, 5600k, 98 cri. Although it is "self-serving" check out their website for some very good info on high CRI leds. (At this page: https://www.yujiintl.com/high-cri-led-lighting.html )
I've had these COBS on my electronics bench for much too long, intending to retrofit my lighting system with them. To my eye, the light is very sun-like and colors look good. Electronically, they drive as the spec sheets say, and I have heat sinks, mounts, and reflectors for them. There is a spot on the COB to mount a thermocouple, so I did so for testing and found that the heat sinks I have dissipate enough heat passively to avoid taking the COB anywhere near its "do not exceed" temperature. Now all I have to do is wire a few more up and start using them. . . .

--Chris S.

Andy Davies
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Post by Andy Davies »

I have found that anything bigger than a single die doesn't add any more light on a Zeiss microscope (Ultraphot and Univeral 16) and already fills the field.

Pau
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Post by Pau »

Andy Davies wrote:I have found that anything bigger than a single die doesn't add any more light on a Zeiss microscope (Ultraphot and Univeral 16) and already fills the field.
I tend to agree, at least if you use -like I do- the original Zeiss collecting optics designed for the lamp filament size. No problem for covering the normal microscope field although I have experienced the peripheral yellow color issue pointed by Charles when I do direct projection with Nikon CF that provides a much larger field.

My experience with LEDs is pretty limited, but I'm very satisfied with the Cree XM-L2 4500-5000K I use in three different illuminators for my Standard 18 and WL scopes.
Doing custom WB I find the color very good, although very likely I'm less exigent than some of you. My main concern is the difficulty to dim it at low power, I solve it with ND filters.

Time ago I used an illuminator with COB LED made by RetroDiode and it was was clearly less convenient.
Pau

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