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Measuring some 365nm UV leds for fluorescence

 
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harisA



Joined: 03 Jul 2011
Posts: 495
Location: Greece

PostPosted: Mon Jan 30, 2017 3:01 am    Post subject: Measuring some 365nm UV leds for fluorescence Reply with quote

It is a common practice in this forum,members let us climb to their shoulders so we can see further. This thread is a small payback.

This is a comparison between a cheapo 365nm Chinese "Cree" led and a superior Nichia led. I was inspired by Pau's thread: http://www.photomacrography.net/forum/viewtopic.php?t=32736&highlight=
and some spectacular images he took using the "Cree" led.
The Nichia led is identical with the one Charles Krebs used recently in the following thread. http://www.photomacrography.net/forum/viewtopic.php?t=33112

To make things simpler I used the "torch" versions of both leds.

The two candidates




To measure the leds I used the following UV meter with a range 290nm-390nm.


[Edit AdminCR - a few spaces added to enable the links to work]
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harisA



Joined: 03 Jul 2011
Posts: 495
Location: Greece

PostPosted: Mon Jan 30, 2017 3:05 am    Post subject: Reply with quote

Before giving any numbers here are some images which are very revealing of the capabilities of each led:

Chinese cree led:(1/10sec f/5.6)



Nichia led:(1/100sec f/5.6)





I measure the leds bringing the torch in contact with the instrument



The cree led gives a measurement of approx. 0.5mw/cm2.My instrument has a range of 0-20mw/cm2
The nichia led gives over the range values even from a distance.
To make a measurement i had to use several nd filters in series.
I find out that the nichia led emmits a minimum of 250mw/cm2 -over 500 times the output of the chinese!
To have a point of comparison the sun at its maximum height (14:00 hour) in Greece during the winter gives a measurement of 2mw/cm2
I will suggest to always use protective glasses with this led (i use a pair of green plastic suitable for 405nm violet laser)
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ChrisR
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Joined: 14 Mar 2009
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Location: Near London, UK

PostPosted: Mon Jan 30, 2017 3:56 am    Post subject: Reply with quote

That's interesting. I have a couple of Chinese <$5 torches. One is claimed to be 365nm, another 405nm and another Deep Purple/UV.

They're very similar to each other. The last description seems to be reasonable . They show a lot of visible light, but ARE definitely "exciting" for revealing the markings on banknotes. A bottle of fluorescein dye also comes to light in front of all three, about equally.
A "405nm" laser has a similar ratio of reactions.
Does your "Chinese" torch excite banknotes? (Are they still available in Greece?Wink)

"Black lights" designed for money testing, and discos, have a dark envelope. So far I've not found that material cheaply/easily purchased separately.

Some ebay vendors of "UV" torches do make a distinction between their "365nm" torches, and others they also sell. WOrth investigating maybe.

I remember using EPROMs, when we used an environmental testing lamp to clear them. We just held them against it for a minute or so. The cover leaked light, which would darken the skin on a hand placed over it, in about the same time Shocked .
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johan



Joined: 06 Sep 2011
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PostPosted: Mon Jan 30, 2017 4:48 am    Post subject: Reply with quote

harisA wrote:
...I find out that the nichia led emmits a minimum of 250mw/cm2 -over 500 times the output of the chinese!


Good test! I don't have a tool to measure UV, but I also did some comparisons between the cheapo ebay units sold as UV, and expensive Nichia-driven torches (Nitecore, MTE). The Nichia chips were simply leagues ahead - this graphic shows the extent:



My info about UV lighting is at http://extreme-macro.co.uk/uv-macro-lighting/
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zzffnn



Joined: 22 May 2014
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Location: Texas USA

PostPosted: Mon Jan 30, 2017 7:06 am    Post subject: Reply with quote

Thank you very much, harisA. Your result is much appreciated.

I mistakenly thought that most commercial UV flashlights are equally terrible. But clearly that is not the case, as shown by your test and Charles' images.

I have that Chinese UltraFire "UV". It does produce VERY WEAK chlorophyll fluorescence using an oil darkfield condenser (essentially oblique illumination from side), but it was soooo weak that I have not cared to use it. I should have bought that Convoy one.
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ChrisR
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PostPosted: Mon Jan 30, 2017 7:24 am    Post subject: Reply with quote

My single-led "cree" ones are far better than the multiple-led ones.
I've ordered one (~$4) which specifically claims 365nm, but from China so could be a while.
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harisA



Joined: 03 Jul 2011
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PostPosted: Mon Jan 30, 2017 8:11 am    Post subject: Reply with quote

ChrisR wrote:

Does your "Chinese" torch excite banknotes? (Are they still available in Greece?Wink)

.


Chris the excitation is very weak like in the first raw of images in the Johan post.The chinese led is severely polluted with excessive visible light.
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harisA



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PostPosted: Mon Jan 30, 2017 8:17 am    Post subject: Reply with quote

johan wrote:
harisA wrote:
...I find out that the nichia led emmits a minimum of 250mw/cm2 -over 500 times the output of the chinese!


Good test! I don't have a tool to measure UV, but I also did some comparisons between the cheapo ebay units sold as UV, and expensive Nichia-driven torches (Nitecore, MTE). The Nichia chips were simply leagues ahead - this graphic shows the extent:



My info about UV lighting is at http://extreme-macro.co.uk/uv-macro-lighting/


Johan i came across your article about uv leds several months ago.It is very informative.It seems that there is a fast progression in uv led technology and the prices will go down vey soon.The nichia torch cost my 20euro from gearbest including shipping.
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Pau
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PostPosted: Mon Jan 30, 2017 9:34 am    Post subject: Reply with quote

Haris, Thank you for the test!
Are you sure that the measurements are right?, I would have expected a clear difference but not up to this level.

My "non Cree" 365 LED is absolutely useless without an emission filter because it emits a big amount of white light -like your pictures clearly show- , but used with the adequate filtering it has proven to be useful for fluorescence. I don't doubt at all that the Nichia will be better, just I didn't find it for sale at low enough price when I bought my LEDs.

I was waiting that Nichia releases new models with intermediate power between their 700mA and the monster 4500mA but likely I'll buy the 700mA.
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harisA



Joined: 03 Jul 2011
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PostPosted: Mon Jan 30, 2017 10:06 am    Post subject: Reply with quote

Pau wrote:
Haris, Thank you for the test!
Are you sure that the measurements are right?, I would have expected a clear difference but not up to this level.

My "non Cree" 365 LED is absolutely useless without an emission filter because it emits a big amount of white light -like your pictures clearly show- , but used with the adequate filtering it has proven to be useful for fluorescence. I don't doubt at all that the Nichia will be better, just I didn't find it for sale at low enough price when I bought my LEDs.

I was waiting that Nichia releases new models with intermediate power between their 700mA and the monster 4500mA but likely I'll buy the 700mA.


Measurements were also a surprise for me and for this reason i check them many times.Your images and their exposure times sounded to good to be true.Unfortunately i don't have a proper uv pass filter to block visible light . However i can't be 100% sure that my fake "cree" led is identical to yours.You can never trust cheapo chinese stuff.Here is an image of the led inside the cheap torch.



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johan



Joined: 06 Sep 2011
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PostPosted: Mon Jan 30, 2017 11:14 am    Post subject: Reply with quote

harisA wrote:
...The nichia torch cost my 20euro from gearbest including shipping.


That's a really great price and truly shows the speed at which this field is moving! The equivalent Nichia-chipped torch would have cost between 100 and 200 Euros only a couple of years ago... great stuff!
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johan



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PostPosted: Mon Apr 03, 2017 9:48 am    Post subject: Reply with quote

Just wanted to add, I've ordered and received one of these now, and it looks like very good value indeed. Comparing it side by side with some of the expensive UV torches I bought a couple of years back, it is definitely true uv (ie 365nm rather than 390), and it has a good focus on it so actually the UV appears in a nice focused small circle, smaller and more concentrated than the other torches I have. Great buy
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