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UltravioletPhotography

Comparing UV LED Flashlights.


colinbm

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Here are two UV LED flashlights that are available in Australia, from the same supplier.

Can anyone comment on these lamps, are they really 365nm, are they narrow band or wide band, are their outputs as stated, are they any good for UV photography ? ?

 

Nitecore CU6 Chameleon UV Ultra Violet 365nm 3000mW (that is 3 watts).

http://www.urbanoutb...0m/Nitecore-CU6

 

MTE Ultra Violet UV 301 Professional Flashlight, Nichia NCSU033B diode, 365nm 658mw (that is less then 1watt).

http://www.urbanoutb...light-36/MTE-UV

 

Is there anything better in the world ?

 

Cheers

Col

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The MTE UV301 that I ordered at Ebay (from a dealer here in Germany) works much better than my homebrew lamp with 365nm 1W input power noname LED. I think it's ok.

 

The power is far beyond any lamp with 5mm Led and visible light of the MTE is darker than vis of any other lamp I ever tested. Including discharging lamps without filter.

 

I don't have any possibilities to measure the output power. I just see the FL.

 

I do not know the Nitecore at all so I can't compare.

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enricosavazzi

I agree with Greenhorn, the MTE 301 is expensive but nonetheless worth its price.

 

The beam is narrowly collimated and the flashlight head cannot be focused/defocused, so if you want to spread the beam onto a surface wider than a few cm you must hold it at a relatively high distance (1 m or more) from the subject, or use a diffuser. Contrary to my expectations, a 2-3 mm thick sheet of the semi-transparent closed-cell white foam material commonly found at be bottom of lens filters boxes works well as a UV diffuser.

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UV-LED flashlights are very good for inducing fluorescence.

 

If used for UV reflective photography, UV-LEDs tend to produce a monochrome look in the photograph because they typically are somewhat narrowband. They will of course enable capture of floral signatures or other UVA phenomena above 350nm.

 

You have to look up the manufacturer's chart for the LED used in the torch to see just how wide its waveband is.

IIRC, the Nichia chips in my torches have about a 10nm half-bandwidth (I think. I should re-verify that.)

 

Manufacturers make LED chips of varying powers. Nichia, for example, makes an A chip which is "stronger" than the B chip used in the torch referenced above. The Nichia "33A", for example, is over a 1000 milliWatt chip.

 

I'm not touting the Nichia - it is just that I've been using those so I know a little bit more about them. "-)

See here for more details on the Nichias: http://www.nichia.co...duct/uvled.html

And do look up the other guys such as Cree or whoever.

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enricosavazzi

I did not try the MTE 301 with my (working but still uncalibrated) spectrophotometer, but it does give the "monochrome" image look that Andrea describes. This is indeed a narrow-band LED.

 

Thinking of it, I have never seen a truly broadband UV LED, nor am I aware of any (verifiably published, with explanation of how it works) exceeding about 20 nm of bandwidth at 50% cutoff. Some multi-chip UV LED arrays have a relatively broadband emission because they use poorly sorted individual dies that emit at slightly different wavelengths, but this is the most "broadband" UV LED I am aware of. One could extend this idea by mixing 365, 380 and 395 nm dies, but the bandwidth would still be a rather modest 30-40 nm, probably with multiple peaks rather than a truly continuous spectrum.

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I see that Johan, has used both these two flashlights, does he still visit these parts ?

 

The Mercury HID lamps I have, seem to deliver the broadest UVA range, but they have spikes too & in IR ;)

Col

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Thinking of it, I have never seen a truly broadband UV LED

 

It is in the nature of the LED beasts that their phosphors do not luminesce broadly. There has been progress made in mixing LEDs to produce white light. So it is probably possible to mix UV-LEDs. I don't think that means simply 'stacking' the chips side-by-side however. "-) It seems to be done on a finer level. (Sorry, I don't remember where I read about this so I don't have a reference.)

I've tried to aim my 365nm and 385nm torches to cover the same (rather small) area, but it doesn't work really well.

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enricosavazzi

Thinking of it, I have never seen a truly broadband UV LED

 

It is in the nature of the LED beasts that their phosphors do not luminesce broadly. There has been progress made in mixing LEDs to produce white light. So it is probably possible to mix UV-LEDs. I don't think that means simply 'stacking' the chips side-by-side however. "-) It seems to be done on a finer level. (Sorry, I don't remember where I read about this so I don't have a reference.)

I've tried to aim my 365nm and 385nm torches to cover the same (rather small) area, but it doesn't work really well.

As far as I know, commercial UV LEDs don't use phosphor. The UV emission is directly produced by electron-hole recombination in the LED junction, just the same as in visible-light monochromatic LEDs. Phosphor-coating is used principally in single-die "white" LEDS, which are actually phosphor-coated blue or "royal blue" LEDs like the Ikea ones.

 

The main problem in building a broadband UV LED that works on the same principle of white LEDs is that the phosphor excitation wavelength (i.e. the emission wavelength of the LED) must be lower that the phosphor emission wavelengths. If we use a phosphor that is excited by 365 nm radiation, then it will likely emit, in the best case, around 380-400 nm, which is not very useful. Of course, the radiation emitted by the phosphor is "stolen" from the radiation emitted by the LED, and there are additional absorption losses, so a LED of this type will produce a broader spectrum at the expense of a much lower emission intensity peak.

 

It is possible, in concept, to use a LED that emits shorter wavelengths, like UVB, and a phosphor that emits at 340-400 nm. The practical problem is that UVB and UVC LEDs at present are very expensive and produce pitifully small amounts of radiation, so we are not likely to see this type of device until things change in this respect.

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enricosavazzi

[...]

Nitecore CU6 Chameleon UV Ultra Violet 365nm 3000mW (that is 3 watts).

[...]

MTE Ultra Violet UV 301 Professional Flashlight, Nichia NCSU033B diode, 365nm 658mw (that is less then 1watt).

[...]

Actually, comparing these power specifications is like comparing apples and oranges. The 3 W specified for the Nitecore is power dissipation, i.e. the maximum electrical power that can be fed into the LED (assuming it is mounted on a very good heat sink) without frying it. The 658 mW for the MTE is output power in the form of UV radiation. Both LEDs are specified for a total power dissipation around 3W. A minor portion of this is emitted as UV, the rest is converted into heat. 658 mW at 365 nm is actually quite a significant amount. How much is actually emitted by the Nitecore is anybody's guess, unless they specify it separately. How usable the emitted UV is, depends also on how efficient the collimating optics are designed to be.

 

The power ratings of LEDs sold on eBay are often fantasy figures. I have seen UV LEDs rated at 5 W that cannot possibly take more than 3 W input power (by simply multiplying their maximum rated current and voltage specified in the lines immediately below the maximum power). Some white LEDs are rated by the producer at 10 W, but the specifications also include a warning that feeding the LED with more than 5 W of input power will significantly shorten its life span.

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Thanks very much Enrico

This is just the sort of info I was needing.

Looking at Johan's photos of UV induced fluorescence, that is the difference I can see.

Yes, beware of rubbery / fuzzy figures......I just didn't have the knowledge to sort out the good from the bad ;)

Cheers

Col

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An important point about using UV LED torches for UV reflected photography (instead of for inducing fluorescence) is that the beam can have hot areas, rings or chip patterns depending on how it is focused/collimated. I have a diffuser filter made by Klaus from a 1.25" UV-Baader filter. I don't know what he used for the diffusion, but it certainly helps.

 

However, the "closed-cell white foam material" Enrico mentioned above for use in spreading the beam might also serve as a good diffuser.

"Spreading" or "diffusing" -- basically the same thing.

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  • 8 months later...

I see that Johan, has used both these two flashlights, does he still visit these parts ?

 

The Mercury HID lamps I have, seem to deliver the broadest UVA range, but they have spikes too & in IR :(

Col

 

OMG, longtime since I visited. Personal life on a bit of a roller-coaster... no time for photography. And actually no room (90% of gear in storage). But cool group of people in this thread, especially hi to Enrico who I know from elsewhere (what a small world!!!).

 

Yes I have both. MTE is a fabulous torch, especially if you filter the output. I would especially recommend Holovachov's images if you want to see beautiful work with it! Very well made product. But yes pricey like all these things.

 

I must try your foam Enrico, I bought a UV emitting ground glass filter and it killed the output by 90%, so gave up.

 

Nitecore CU6 is actually weaker but more narrow, ie less blue spill. Usable, but weak - long exposures. But again a well made torch, with other colours and visible light.

 

Agree that the mw figures given really don't help much especially with eBay torches. Most were a bit of a disaster for me and only really MTE & CU6 were any good.

 

Anyway nice to stop in, don't hesitate to mail via my site if you need some more info.

 

Hopefully once things sorted I can get back into this... some people have been awfully nice to me here and I owe them a large debt of gratitude...

 

-Johan

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Hi Johan

Good to see you drop by again.

Good luck on the roller coaster of life :(

Hope you get back here soon.

Col

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Johan, it's nice to see you back. Stop by and chat as you have the time. We are always here.

 

I've just made a note to check that the Sticky references the MTE torch as it seems to be the most popular amongst our members.

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  • 2 weeks later...
I agree with Greenhorn, the MTE 301 is expensive but nonetheless worth its price. The beam is narrowly collimated and the flashlight head cannot be focused/defocused, so if you want to spread the beam onto a surface wider than a few cm you must hold it at a relatively high distance (1 m or more) from the subject, or use a diffuser.

 

came across this and just wanted to add a couple of points. the MTE can actually be focused/unfocused, it's just hellish stiff so easy to miss. Twist the whole front inc. the anti-rolling hexagon shape, you'll see what I mean. Second, you can take the front ring off and it fits a 38mm filter. There are 38mm-52 adapters on ebay. So with adapters you can just screw on a UV pass filter if you want.

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Focusing is a very handy feature. And particularly so is the filter fitting capability. Some of our posts over the last year have dealt with visible violet/blue "leak" from UV-LED torches much of which is prevented by fitting a UV-pass filter like the BaaderU to the torch. The MTE would make that easier.
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enricosavazzi
Our common friend at uviroptics sells a U340 filter cut to the right size for the MTE 301 (eBay item 291472784315). Much cheaper than a Baader U, and equally effective because there is no need to filter out unwanted NIR (which is not produced by LEDs).
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