High CRI LED source?

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dmillard
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High CRI LED source?

Post by dmillard »

I just found this website this evening: http://www.yujiintl.com/high-cri-led-lighting I haven't yet ordered anything from them, but they look intriguing.
Last edited by dmillard on Thu Jan 21, 2016 4:44 am, edited 1 time in total.

Bushman.K
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Post by Bushman.K »

They claiming CRI 98 and color temperature up to 5600K for VTC series emitters, which doesn't sound realistic, because even top manufacturers don't offer anything like that - high CRI currently means "warm white".

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Post by ChrisR »

I had to truncate the link to http://www.yujiintl.com
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dmillard
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Post by dmillard »

Thanks Chris - I just removed an errant terminal period, and the link is now functional.

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Post by ChrisR »

That's better :) - the sliding pencils/cri display is revealing.
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Asha
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Post by Asha »

Bushman.K wrote:high CRI currently means "warm white".
I find this a little misleading. It may be true that the highest CRI LEDs are of a warm-white color temperature, but there are relatively high CRI emitters along the entire color temperature range.

Many video light manufacturers have high-CRI daylight products. The highest I've seen for daylight color temperature is CRI>95 which means it will be at least 95, perhaps higher, but no guarantees :)

Having said all that, I really find that LEDs give terrible color rendering as compared to either halogen or flash, even if they are advertised as high CRI. In reviews of LED lighting for photography and video, I often see comments that there is terrible color cast that needs extra work to remove in post-processing. In looking at the spectral curves, LEDs are heavily weighted, with profound absorption bands along the visible spectrum, even the high CRI ones. Of course, YMMV.

ETA: The website listed above says "Yuji high CRI LED series has CRI values up to 98 with R9-R14 values all over 90". So basically that is a CRI>90 spec.

Bushman.K
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Post by Bushman.K »

My statement could be "misleading" only in case when it's taken out of context.

You can go to any major electronic components store such as Digikey and do a parametric search. Setting CRI 98 and CRI 98 (Typical) parameters as a requirement will narrow your results to LED Engin brand and 2700-3000K color temperature range.

Doing it backwards by setting 5600K will again narrow results down to top CRI equal to 95, and it's only a single brand Luminus Devices Inc. with several COBs.

For sure, we can speculate about that, but usually, when there is certain "super-product", especially offered by continental Chinese company, and nothing similar by its key features is offered by major manufacturers (in this case - Philips, OSRAM and so on), that always looks suspicious for me.

Lighting products are quite different from LEDs. These can include filters or have mixed set of LEDs, forming any color temperature you want. But it definitely doesn't serve as an evidence of existence of similar LEDs.

Personally, I'm using Bridgelux 35W module as portable constant light source and I'm relatively satisfied by it, while I have to use custom color balance preset - neither 3200K nor 3100K standard settings working for it because of reddish cast.

So, what I'm trying to say is that I would think ten times before purchasing stuff with "super-specification" from continental China.
Last edited by Bushman.K on Fri Jan 22, 2016 11:43 am, edited 1 time in total.

Chris S.
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Post by Chris S. »

I wouldn't be so quick to bash Yuji LED's claims. As David wrote, their products are "intriguing." Just as we can't accept claims without testing, neither can we dismiss them without testing.

Yuji says that their LEDs have a bit better CRI than the competition. And when Kirill surveys the competition, the competition does indeed look a bit worse in CRI. So it's appropriate for someone to test the claim and report back.

--Chris

Bushman.K
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Post by Bushman.K »

Curiosity would cost at least $40 for a candelabra lamp and even more for more usable products. There is a chance for surprisingly good specs. But personally, I wouldn't invest more than ten bucks in testing, keeping in mind, how small that chance is.

g4lab
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Post by g4lab »

Well one thing that I haven't seen before which these have , is the use of
violet excitation which moves the excitation peak more out of the visible range compared with existing LEDs.

Their propaganda is impressive. I do know that lighting manufacturer's stretch lab data till it screams. This is a holdover from days when there were only big old venerable companies making lighting.

the price to test is a bit high.

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Post by Chris S. »

A lot of us here have spent $40 (and up) over and over on tests. A $40 lens, for example, might be called "cheap." The bigger cost is time. To conduct and post a solid test of the product would take many hours. If one's time has any value, this dwarfs the cost of the LED.

Yuji does, by the way, entertain requests for free samples for commercial applications. While a test for our forum is not a commercial application, what we publish here drives purchases, so the company might well be interested. NB, the recipient of a free sample pays shipping from Beijing, so it might actually be cheaper to go ahead and buy the product closer to home.

--Chris

Charles Krebs
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Post by Charles Krebs »

When I was gathering the parts to make my lights (early 2015) I was interested In a "VTC" COB they showed on their site. It had the "98 Ra" tating and had decent light output (I seem to remember it was 8 or 9 watts. But it was "sold out" and is now no longer listed as a current product on their site. All of the currently listed "VTC" leds are of too low light output to be useful for a nice light. The "BC" series look interesting but their R9 value (CRI TCS Value) is stated as: >70, while the Bridgelux has an R9 of 98 (granted, it is a much lower CCT of 3000). Still, it might be interesting to see what their 5600k "BC Series High CRI COB LED - 135L -" would do in a light... maybe battery powered for use as an "auxillary" for field macro work.

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Post by Chris S. »

Elsewhere, at least two fellows have tested Yuji's products before opining on them. One is Scottie Wang, "Yuji High CRI Bulbs tested," posted at dpreview forums. Over a couple of posts, he shows instrument analysis of the Yuji VTC 5600K, and summarizes thus:
  • "Incredible results!!"

    "This bulb is rated CRI 97+ in their catalog, and my measurements has proved it. My results is pretty similar to theirs published on their web site. I can only speak it's the highest CRI LED bulb I've ever measured. From my own test. it's slightly better than continuous LED light source "Aputure Amaran AL-H198C" which is CRI95+ measurement confirmed."
Another tester is Matt of DIY Perks, who posted a demonstration on YouTube comparing a Yuji BC Series High CRI COB 5600K 100W LED with sunlight. This LED and sunlight look pretty close in the video (check about a minute and a half in), even though the Yuji BC series is a step down in CRI from the Yuji VTC series. If this is not the exact item Charlie just mentioned, I think it's something close. Yuji claims CRI 95 for this model. Matt's measurement with a spectrophotometer is a hair better, at CRI 96. As Charlie suggested, it might make a very nice field light for macro.

It's noteworthy that Matt obtained a free review sample from Yuji; they might well extend the same courtesy to a tester from our forum. It would also be interesting to ask Yuji if the VTC COB that Charlie referenced, or a similar replacement, is expected to return to the company's offerings.

--Chris

Charles Krebs
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Post by Charles Krebs »

An interesting page (and some video links) is seen here:
http://www.oscars.org/science-technolog ... ing-report

One thing of interest to me are the split Macbeth charts at the bottom of the page. This organization (and it's report) appears to be primarily interested in how LED lights can be used with the long-time standard (Tungsten balanced) movie film stock. Unfortunately the brands and specs of the LEDs used for comparison are not given. I can see no indication of when this was done (and LED technology is improving at a rapid pace). So I would certainly not take these results as "Gospel" in regards to the current state of LED illumination. But it is one of the few places where I have seen a nice direct comparison.

Also, tungsten film stock has it's own sensitivity characteristics, and we are interested in digital cameras.

It seems that a better "index" than CRI for digital photography might be the "TLCI" ratings (Television Lighting Consistency Index). But is is not widely used. Some information can be found here (and many other places):

http://www.gtc.org.uk/media/fm/Zerb%20a ... CI_web.pdf
http://www.cineolighting.com/wp-content ... andard.pdf
http://www.gtc.org.uk/members-area/tlci-results.aspx
http://www.gtc.org.uk/members-area/tlci ... sults.aspx (actual ratings of a large number of commercial lights, but no individual LED COBs)

Yuji certainly seems to be concentrating their efforts on very high CRI pieces. Had an 8-10 watt, 5600k, "VTE" COB been available I would have tried them. As it is, the readily available Bridgelux Vero Decor (3000k) looked as good (if not a little better).

I must say, an "outdoors macro light" using the "BC Series High CRI COB LED - 135L -" sounds tempting to try
:wink:

Asha
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Post by Asha »

Here is a nice rabbit-hole to explore--lots of discussion on battery powered LEDs, aka flashlights :)

http://www.candlepowerforums.com/vb/forum.php

Some of the folks in the Candlepower Forums have done tests on individual LEDs, and also flashlight mods, substituting higher quality LEDs.

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