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365nm UV torch

Posted by Henri Koskinen  
Henri Koskinen March 07, 2017 09:48AM
Hello Sirs, wanted to share this with you as it is a game changer in low budget UV photography.

I bought a dedicated Raytech 6 + 6 W UV lamp about 5 years ago for about 400 dollars as it was the best price/quality solution for photographing mineral fluorescence back then. That was then and now is now. The pictured UV torch sells for 20 dollars and is way more powerful in terms of UV flux than my Raytector.

The torch is based on Nichia 365nm UV LED and uses one rechargable 18650 Li-ion battery.

I did a little comparison and tried to evaluate the max. relative luminous flux per unit area from the two sources for an area that is small enough to be inside the cone of light from the flash. I had about the same brightness with the following values of exposure. This is for about one square centimeter and both Raytector and torch as close as possible to the fluorescent subject, For wider area the results would not have been so bad for Raytector

Torch ISO100, 0.5s, 5.6
Raytector ISO1000, 20s, 5.6

In terms of max luminous flux per unit area the torch is about 400 times more powerful than my Raytector. Part of this is explained by the fact that the big and clumsy Raytector is difficult to position really close to the subject whereas with the torch this is easy. This means that the torch makes low budget microphotography of fluorescence possible. I am using a 20x 0.42 Mitutoyo microscope objective with long working distance attached straight on a 100mm tube lense. So this is a single 10x image straight out of camera and shot with ISO100, 0.5s, f5.6 (fluorescent Hazel leaf)

Using the same setup with same exposure parameters, just replacing the torch with Raytector gives this image

Really nothing to see here. Should have used ISO1000 and 20s, but then the noice would have been really bad and even little spill visible light would have pretty much washed out the fluorescence.

Here's the torch


Here's discussion about the torch


Here's a test for the torch



Edited 1 time(s). Last edit at 03/07/2017 11:15AM by Henri Koskinen.
Alfred L. Ostrander March 07, 2017 02:08PM
One thing to be said about the inexpensive LED lights now available is the lenses have no specified filtering capacity and they can range from about 365 to 395 nm.

For a recent family outing at a location where long wave light would be quite sufficient I bought 4 Ray-O-Vac LED lights at US $9.97 each. We were in the woods on a sunny day but they gave off enough light to locate good specimens for further evaluation. Great family fun at a bargain price. Everyone found something and everyone had their own light. Thing is, the unfiltered LED light behaves much differently than filtered. I read the specs on the $20.00 light you cited and it said nothing about the filtering capacity or quality of the lens. A friend of mine has a generic LED light he paid $40.00 for. It does have a good filter on it. All other factors equal, his light gives a much truer color when compared to a high quality light. The lights I bought tend to look washed out. Sliding a piece of good long wave filter over my lamp vastly improved the results. The results then compared favorably with the filtered LED and my small Raytech. So the bargain price LED lights were sufficient for the needs of a day trip. For good photography, I would not use them.

Henri, nowhere near the information you presented, just empirical experience and an awareness of good filters for UV lights along with a respect for the cost of appropriate filter materials. Maybe it will give you ideas on what to look for regarding filter lenses and price comparisons.
Henri Koskinen March 07, 2017 03:01PM
Hello Alfred,

these new 365nm Nichias are way beyond any other cheap "UV" torches previously available. There is very little need for a filter cutting the long end as there is really very very little visible light emitted. Look at the spectral power distribution graphs available in the last link in my post.
Steven Kuitems March 07, 2017 04:11PM
Henri, let us know when you find an economical lamp for the short wave ultra violet range, or one that has all three long, mid and shortwave range selection.

Jyrki Autio March 07, 2017 04:18PM
Hello Henri.

Interesting topic and expected results.
I have been experimenting with LEDs lately and plan trying also UV LEDs this same way:

Here 3 x 5W Yuji COB LEDs are brought within 2cm of the target. Plenty of flux.
This same setup could be used with UV LEDS. I thought about using 254nm ones maybe with band pass filter.
Does anyone have experience of these shorter wave UV LEDs with minerals.

Reiner Mielke March 07, 2017 05:02PM
From what I can see the short wave LED's have only a small fraction of the output of the LW. https://www.intl-lighttech.com/products/light-sources/leds/uv-leds You would need hundreds of SW LEDs to equal one LW LED.
Henri Koskinen March 07, 2017 05:06PM
Hello Jyrki,

this LED stuff is evolving fast. 365nm leds comparable to the 365nm Nichias cost several hundred dollars just 2 - 3 years ago. Nichias only sell LW LEDs from 365 up, there could perhaps be some consumer regulation issues involved with SW sources.. I bought two 365nm Nichias for 40 dollars including postage, which is an amazing bargain. The UV flux they generate is more than enough for 20X microscopy. Now all that is missing are the amazing images :-)

In case you are not aware some guys at photomicrography.net are playing with similar constructs as yours.
Jyrki Autio March 07, 2017 06:21PM
Thanks Henri, I will look at Nichias and wait to see those images.

-Reiner. Radiating power in 254nm is only couple of mW but they are small in size and if they can be brought close enough to the object it could work.
Area to illuminate could be in range of 10-20 mm2 and distance 10-20 mm.
Joel Dyer March 08, 2017 06:27AM
Hi Jyrki,

If you're looking to get high-quality UV LED sources for macro / micro work for example Thorlabs and Roithners could be one place. But then you would probably end up spending a few hundred I think on LED+mounting-cooling and controller/ beam expander.


Laser needs even lower power levels for equivalent work, but then properly stabilised, narrow bandwidh UV laser light systems are even more expensive due to the need for pricey controller / power units. This is eventually what I'm dreaming of...

I would definitely use a shortpass filter myself if the wavelength of the cheap UV LED is not guaranteed and stabilised, or even if it was claimed to be fairly narrow. If the power level / wavelength fluctuates then you'll be getting various fluorescence reactions from different activators. A good shortpass filter from, say, Edmund Optics or Thorlabs might be worth the cost.


On the other hand, if you want to filter out the cheap UV light's violet / blue light then indeed a longpass filter positioned in front of the LWD objective would be recommended.


Personally, I don't trust unstabilised cheap UV LEDS / Lasers, as how can their operating tempature, voltage, current and wavelength possibly be gauranteed? When you're operating cheap lights for 5 minutes, 10 minutes or an hour, there's bound to be variation. That's why quality stuff (so far) costs more - but hopefully one day in the near future things might change..?

You see, even though my own new 3000€ (+ VAT) laser is a stabilised SLM system, its wavelength has to be confirmed and entered into the system every single day after it's stabilised in a few minutes....One day it can be 531.5xxxxx and another it can be 532.00xxxx. Gas lasers are another matter.

This is just some thoughts after carrying out my own modest photo / spectroscopic / Raman work... with both cheap and expensive light sources.

Dr. Paul Bordovsky May 06, 2017 08:41PM
Alfred, the flashlights with the Nichia LED do not come with a filter. You have to order that separately. It is called a ZWB-2 filter. Not sure I can give a link here to a source, but just google it. They are about $2-$4 depending upon the source. The flashlight is very much better than the other previous LED longwave torchs. Minerals not known to fluoresce previously are glowing now. Elmwood calcite even glows a little at the edges.
Douglas Bank August 06, 2017 06:08PM
The Convoy light (which is the brand sold by Gearbest and a number of other resellers from China) and the Nichia 365nm LED are game changers in the fluorescent mineral world. They are fantastic little beasts. The only problem is what Paul mentioned - minerals not known to fluoresce are glowing now. This means that we now need display lights using this LED or similar in order to show off our new finds. It also means that if you use this light while collecting (in the field or at a show), you might find something that looks great, but wont light up at all using your regular tools. I was at Don Newsome's house (maker of the Superbright), and we went through his extensive collection with this little light. It caused many existing spectacular short wave only specimens to fluoresce in new colors long wave, implying there are more minerals there than were previously known.

As for the filter, if you are using the light for photography, the ZWB1 filter (20mm, by the way) will cut out even more visible light (including some visible UV at the upper end of the range). It does so at a cost of a lot less 365 transmitted light, but for photography, you can just take a longer exposure. The ZWB2 filters are very cheap and usually available.

Everyone who has seen one of these lights in action has decided to buy one. It isn't as cheap as $25 because you probably want to get a couple of batteries and a charger, and that can cost you $40 if you get quality materials, but it is still pretty cheap, easy to stick in a pocket, and can easily cause minerals to fluoresce visibly even in a lighted room. (AND it is the best pet stain detector I have ever used ;-)

(BTW, I think there are many problems with 254 LEDs. Way too expensive, too dim, short lifespan and they self fluoresce. I wouldn't hold my breath waiting for one.)
William Smith October 27, 2017 08:26PM
For those who need a source for the ZWB1 uv pass filter to fit the convoy light, here is a link.
JL October 27, 2017 11:49PM
Thanks William, I just bought one ;)

By the way, after reading this thread I decided to get my hands on one of those Convoy light.

Amazing !
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