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#1 Andrea B.

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Posted 11 July 2015 - 15:06

Sticky :: UV-Induced Visible Fluorescence
by Andrea G. Blum
for UltravioletPhotography.com

Last Update: 10 Dec 2020
Reformatted. New links.

Sticky List:
<> Sticky :: SWIR Photography: Cams, Mods, Lenses, Light, Links <>
<> Sticky :: UV-Capable Lenses <>
<> Sticky :: UV Induced Visible Fluorescence <>
<> Sticky :: UV/IR Books <>
<> Sticky :: UV Photography: Cams, Mods, Lights, Links <>
<> Sticky :: UV/Vis/IR Filters <>
<> Sticky :: White Balance in UV/IR Photography <>

Post Search Tags:
Conical Cells Filters Fluorescence Infrared Insect Vision LWIR Multispectral SWIR
UV Camera UV Lens UV Lighting UV Portrait White Balance

Note from Editor:
This is a joint effort by the members of various forums who enjoy UV-induced visible fluorescence photography. Thank you to everyone for their input.

Please PM Andrea B. on UltravioletPhotography.com with any corrections, additions or suggestions.

UV-Induced Visible Fluorescence (UVIVF)

The type of luminescence most often encountered in UV photography is the immediate visible light emission, or fluorescence, from a subject when stimulated by UV blacklight. Fluorescence is caused by an object's absorption of high energy (shorter wavelengths) ultraviolet light photons which then excite the object's electrons to a higher quantum state. The electrons immediately relax to a lower quantum state and emit photons of lower energy (longer wavelengths) in the form of visible light. This visible fluorescence may be successfully photographed.

Not every subject fluoresces. UVIVF beginners might enjoy starting with fluorescent minerals, clothing, leaves, lichens, flower parts and tonic water. Note that it is possible for UV light to also induce Infrared fluorescence in some subjects. Similarly, Visible light may induce IR fluorescence. Much of the following information about Visible fluorescence can be easily translated to apply to UV-induced Infrared fluorescence with appropriate filter changes.

Equipment for UVIVF Photography

(1) UV Blocking Goggles --OO--
UV light is dangerous to your eyes!!
Heed the warnings we have posted in [UV SAFETY] UV and Your Eyes :: UV Safety Reference
Use your UV-blocking goggles when shooting UVIVF. --OO--
Please do not attempt to fluoresce other humans or live animals. You could damage their eyes.

(2) Camera and Lens for recording a visible light fluorescence photograph.
With proper filtration and good UV illumination, stock cameras and lenses are the natural choice for UV-induced visible fluorescence photography. So your primary expenses for UVIVF photography will be for UV lighting and for the excitation and barrier filters discussed below.

(3) Dark Room in which to photograph UVIVF.
Yes, for the very best results we photograph visible fluorescence in the dark because ambient visible light will cause unwanted reflections off the subject which will contaminate or wash out the emitted visible fluorescent light. As a practical consideration, your Dark Room (or Dark Closet, perhaps) should contain a lamp or a handy flashlight to allow you actually see the equipment and subject while setting up for the UVIVF photograph.
Remember to take your UV-blocking goggles with you into your Dark Room. --OO--

(4) UV Light Source
The UV light source must be filtered to ensure only UV light reaches the subject.
  • UV-LED Flashlight (aka Torch)
    Its easier to add a UV-pass filter to a torch than it is to a mercury lamp. Most available UV-LED torches have peaks between 365 nm - 400 nm, but more are becoming available. We would suggest that your first UV-LED torch be at 365 nm which is deep into the UV range that any stray violet or blue output from the LED can be filtered out. There are more remarks about violet light leaks in the UV-Pass Excitation Filter section below.
    The first two links are randomly chosen just so you can see what the torches look like.
    Please buy from your preferred vendor and look for reviews here on UVP.

  • Mercury Lamp
    Lamps are typically filtered by the manufacturer. If not, it may be difficult to find excitation filters large enough to fit a lamp.
    Example: Blak-Ray B-100 AP Lamp for UV & UVIVF Photography
  • UV Flash
    It is possible to induce visible fluorescence with UV flash. However, if the fluorescence is dim, then a longer exposure with repeated flashes during the interval might be needed. Your particular camera and flash will determine whether the flash can be set to automatically repeat fire or whether you will have to manually re-fire the flash. [Example and LINK]
  • UV Lighting Tag
    For more information all UV illumination, find all tagged posts: UV Lighting
(5) UV-Pass Excitation Filter on the UV light source.
The purpose of the UV-Pass excitation filter on a UV light source is to block all non-UV light leaks often seen with UV light sources. Such non-UV light leaks could cause non-fluorescent visible or infrared light reflections off the subject that might contaminate the visible fluorescent light emitted from the subject. And any non-UV light leaks could also potentially cause additional fluorescence depending on the subject being photographed.

We are using the word leak informally. For example, UV-LEDs have a fairly narrow bandwidth and steep shoulders. But the cutoffs are not sharp, so there can be some visible violet output under the right shoulder for a 365 nm peak torch. Call that a "leak". A 375/380 nm peak torch certainly will have some violet output and possibly even some low blue (indigo) output.

It is more difficult to filter Xenon UV-flashes, but it must be done because there can be a great deal of IR output from a Xenon flash.
  • Excitation Filter Example: Hoya U-340 (preferred) or Baader UV-Pass
    The Baader UV-Pass filter has a little bit of violet transmission under the right shoulder. The U-340 is the currently preferred filtrationnto block stray violet/blue light from UV light sources. The linked example shows this very well.
  • Violet Leak Example: an unfiltered UV-LED shiny spoon test.
  • See more about excitation filtration in the Shiny Metal Test below.
  • For more filter information, find all tagged posts: Filters or see <> Sticky :: UV/Vis/IR Filters <>
(6) UV/IR-Cut Barrier Filter on the camera lens.
The purpose of the UV/IR-cut barrier filter is to exclude all non-visible light from reaching the sensor. A stock camera's internal filtration may not totally exclude UV or IR wavelengths from reaching the sensor. This is OK for ordinary visible photography because the very small amounts of UV just past 400 nm or IR just beyond 700 nm which might be recorded do not really affect a visible photo. However, when attempting to capture dimmer visible fluorescence emissions, which usually entail exposures in seconds, we must be careful that stray UV light (mostly recorded in the blue channel) or stray IR light (mostly recored in red channel) do not contaminate the photo. (Note: IR light is a much harsher contaminant of visible photos than is UV light).

So to ensure you are recording only visible emitted fluorescence, add a good UV/IR-blocking filter to the lens. Do carefully test any stock camera which is to be used for UVIVF work to see whether a seconds long exposure in UV-only or IR-only illumination can be recorded thus indicating weak internal filtration.

Ancient History Side Trip: Leica had an enormous kerfluffle involving weak internal filtration against IR when they first brought out their digital rangefinders. They had to send free IR-blocking filters to everyone who bought an M8. And even early Nikon and Canon DSLRs had weaker IR blocking than they do today. This caused some interesting problems when photographing black synthetic materials which came out looking rather pinkish-pale.
  • Barrier Filter Example: Baader UV/IR-Cut Filter
  • See more about barrier filtration in the Shiny Metal Test below.
  • For more information, find all tagged posts: Filters

Shiny Metal Test in UVIVF Photography
from UVP member Shane Elen

Capturing fluorescence (spectrally or photographically) works on the principle that the combined effect of the excitation and emission filters allows only fluorescence emission to reach the camera sensor. Excitation wavelengths from the excitation illumination must be totally excluded. For UV-induced Visible Fluorescence photography,
  • the UV illumination must be filtered for UV-only output, and
  • the lens must filtered for Visible-only input.
Typically very narrowband filtration is used in laboratory fluorescence photography. Here on UVP most fluorescence photography makes use of rather broadband filtration because narrowband photographic filters are not readily available.

To test that the filtration is working properly, photograph some shiny ball bearings or a shiny spoon (which are non-fluorescent, of course) in total darkness. If the filtration is working properly, then the ball bearings or spoon are not visible. If the spoon or ball bearings are visible (showing a shiny reflection), then there is leakage in the filtration which must be remedied in order to claim proper UVIVF photography.

When using a broadband camera or a camera with a weak internal filter, it might be difficult to determine whether filtration leakage in the Shiny Metal Test is from stray Visible or stray Infrared output from the UV illumination source or whether it is from some UV getting through a mediocre UV/IR-blocker filter on the lens. Further tests using additional filtration might be useful to sort this out.

I don't have a statement to make at this time about whether the length of the exposure time might mitigate the effects of any unwanted stray light output from the UV illumination source.

LINK to Shiny Spoon Tests
Following these links, I've posted two photos from the tests. However, please do note that since these tests we have all begun to use Hoya U-340 filtration on the illumination source to better block violet light passage. I did not have that filtration at the time. .
Shiny Metal Test: Photo 1
Camera: D600-broadband
Filtered Lens: Zeiss 60/4.0 UV-Planar with Baader UV/IR-Cut Filter
Unfiltered Torch: Nichia 365 UV-LED Flashlight
Exp: f/4 for 1.6 @ ISO-400 in total darkness
The lens is filtered to permit only Visible light to be recorded.
The unfiltered UV flashlight produces visible violet leakage.

Attached Image: leak.jpg

Shiny Metal Test: Photo 2
Camera: D600-broadband
Filtered Lens: Zeiss 60/4.0 UV-Planar with Baader UV/IR-Cut Filter
Filtered Torch: Nichia 365 UV-LED Flashlight with Baader-U UV-Pass Filter
Exp: f/4 for 1.3" @ ISO-400 in total darkness
Again, the lens is filtered to permit only Visible light to be recorded.
The violet leakage from the UV flashlight is reduced to almost nothing
when a UV-pass filter is used on the source illumination.

NOTE: Use a Hoya-340 filter to fully block violet passage.
Attached Image: noLeak.jpg

White Balance in UVIVF Photography

A Brief Review from reflected UV or IR photography:
For reflected UV or IR photography, it seems reasonable to consider "white" to be a reflection of all of UV, Visible and IR wavelengths. So we use uniformly UV/Vis/IR-reflecting materials such as Spectralon (uniform) or PTFE (almost uniform) as white balance targets in reflected UV/IR photography. Given that both reflected UV or IR photography produces false colours, then, strictly speaking, white balance is not a necessity. But we often perform white balance processing in documentary UV or IR photographs in order to standardize the false colour outcome over differing gear platforms.

Analogously, it seems reasonable to use some kind of white fluorescent material in order to perform standardized white balance for the visible fluorescence induced by UV light. But finding such a material or pigment which fluoresces white or grey under filtered UV (in the dark) has been a problem. Neither clean, uncontaminated Spectralon nor PTFE is white-fluorescent so we cannot use those materials. Some pigments fluoresce an "almost white", but it is more of a blue-white. The search goes on for an inexpensive white-fluorescing object.

Recently UV Innovations developed the UV-Grey™ fluorescent target for use in standardized white balanced fluorescence photography where emissions are induced with UV illumination around 365nm. UV Innovations also offers the Target-UV™ with both fluorescent neutral and fluorescent RGB patches for use in determining the intensity of a subjects fluorescence or for white balance and color checking. The targets use a proprietary coating to produce the fluorescence and are calibrated to certain standard filtration. Tests here on UVP show that the UV-Grey™ or Target-UV™ cards work quite well for white balance of UV-induced flurescence, the only drawback being that they are quite expensive.
[Disclaimer: UltravioletPhotography.com is an independent website which accepts no advertising and does not solicit products for testing. We are not affiliated with any manufacturers or vendors.]

Here are some tests with the Target-UV™ and the UV-Grey™.
  • Experiment 1: First Look at Target-UV™ & UV-Grey™ for UVIVF [See Post #7]
  • Experiment 2: Target-UV™ with Stock Cam/Lens & Unfiltered Lens/Light
  • Experiment 3: Target-UV™ with Stock Cam/Lens & Filtered UV-LED
  • Experiment 4: UVIVF White Balance with the UV-Grey™ Target & Stock Cam/Lens
From UVP member John Dowdy:
The long established standard for film fluorescence photomicrography was daylight balanced film. Seems to me that for best reproducibility that should likewise be applicable to digital fluorescence macrophotography.

Unfortunately, the preceding tests have shown that using a digital Daylight white balance setting often does not produce accurate visible fluorescence colours. (See Experiment 4 above.) It is more useful than not, however, so go ahead and experiment with a Daylight setting for UVIVF work. Also try the lowest K setting. Some cameras permit further adjustments of color which might help bring either Daylight or K-2500 white balance settings closer to accuracy.

Other References
from UVP member Shane Elen
The links are for your convenience only. UVP does not receive anything if you click on them.
Andrea G. Blum
Often found hanging out with flowers & bees.

#2 Andrea B.

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Posted 24 February 2019 - 01:54

Filter the lens to block everything except visible light.
Filter the UV-source to pass only UV.
Shoot in complete darkness.

Test for leaks using the Shiny Metal Test described above.

EVEN SHORTER VERSION: Filter, filter, dark. :lol: :rolleyes:

Andrea G. Blum
Often found hanging out with flowers & bees.

#3 Andrea B.

    Desert Dancer

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Posted 10 December 2020 - 22:31

Links have been restored.

Old links were replaced in some places by links to newer information. In particular I added links to Convoy S2+ and Wanfire "Nemo" UV-LED torches and also a link to using Hoya-340 filtration on UV-LED torches, the currently preferred method.

I'm happy to add any links which readers think would help to make the info better.
Your suggestions are always welcomed.
Andrea G. Blum
Often found hanging out with flowers & bees.