Catching a wave

Leaf litter under normal light

I’ve had these images in my folder for a while now, considering doing a post on them, and just realized that we were coming up on a year since they’d been taken, so I’m timing the post to appear on that anniversary, since humans do stupid pointless things like that…

These were from the trip we took to Savannah, Georgia, and for that trip I had a particular goal that never came to pass: I wanted photos of a scorpion, most especially one fluorescing in UV light. Scorpions are nocturnal and more than a little secretive, so spotting them takes luck or an edge, and mine was a recently-purchased UV flashlight. Several nights, I went out wandering around with the light, shining it in every location I thought likely to host a scorpion, but saw none at all. However, every once in a great while I saw something like this:
Leaf litter under ultraviolet light

Note the difference with the top image, and how a few leaves seem a whole lot brighter in the bottom image. To the best of my knowledge, these are playing host to some form of fungus, one which fluoresces under UV. This, by the way, was a 13-second exposure solely by the light of the UV flashlight.

Ultra-violet light, like infra-red, is a band of wavelengths that sits just outside of those we can see, what we typically call the “visible spectrum” – there are no exact demarcations, but generally, UV runs between 100 and 400 nanometers (nm) in wavelength, while what we can see (visible light) is roughly between 400 and 700 nm. This is a very narrow band in the electromagnetic spectrum, outside of which falls everything from X-rays to AM radio, cellphone signals to gamma-ray bursts from supernovae – they’re all just different wavelengths of the same form of energy, transmitted in photons. While our eyes detect this narrow band, coincidentally (or not) the region of the most energetic emissions from our sun that make it through the atmosphere, we can also detect a few other wavelengths with our organs: our skin reacts to both UV (tanning, skin cancer) and infra-red (heat.) But for the most part, we miss most of the remaining bandwidth.

The deep purple light seen above isn’t UV, but the portion of the flashlight’s output that impinged into the bandwidths we can see – regular strength violet, if you like. It’s very dim to our eyes, even though my light source is putting out as many photons as a normal flashlight, they’re just mostly ones we can’t see. Digital camera sensors, however, can usually pick up a range of wavelengths a little beyond what humans see, if they’re not filtered out (they usually are, because capturing them can alter the photo and make some images look different.) But there’s often a little overlap, so the image here is not exactly what I was seeing, though close.

glow in the dark ornamentNow we get to fluorescence. Fluorescence (and phosphorescence, a close relative) is a curious trait where a substance absorbs energy that it then re-emits as visible photons. In cases of UV fluorescence, possessed by some substances, some arthropods, and even some minerals, the UV photons are absorbed into the substance as greater activity in the atom, electrons jumping to a higher energy state. Almost immediately, they drop back down to their ‘normal’ state and re-emit this energy, but at a different level, thus producing a different wavelength, one that we can see. So it’s not like the normal situation we find ourselves in every day, where photons simply bounce off of an object and reach our eye, but a trade, where objects keep the photon energy and exchange it for photons that we can see – a chemical ‘currency exchange’ system.

(The same, by the way, often happens with IR, getting re-emitted as a lower wavelength still detectable to us as heat – think of a black object left sitting in the sun for a while – and often this energy is used in other manners by living organisms.)

Fluorescent lights rely on this principle (yeah, big surprise there,) though technically they’re phosphorescent, since there’s a minimal delay before the energy is re-emitted as visible photons. The tubes have high-energy electrodes at either end with a low-pressure inert gas down the length between them, while the insides are coated with a phosphorescent material. When the bulb is charged up, the gas permits electrons to scatter down the tube in all directions, which strike the material coating the tube – that material absorbs and re-emits the energy of the electrons as photons, causing the coating to glow. You might see on older bulbs a bare patch where the powder has come off the glass, and this appears darker even when the bulb is on – uncoated, the glass is only a window into the inside of the bulb, and the gas within doesn’t glow itself. If you could look down the length of an active fluorescent bulb, it would appear to be a tube lit from the outside.

The old-style cathode ray tubes used in TVs and computer monitors – you know, the ones as deep as they were wide – use this as well. The front viewing screens are coated in phosphorescent materials, and an electron gun within hurls electrons at select areas of the screen (what we usually call ‘pixels’ now, though that’s not exactly accurate,) which will glow momentarily. One gun, with electrons aimed by magnetic plates, will redraw the image one dot at a time, side-to-side, top-to-bottom, sixty times a second or so (that’s actually what the ‘refresh rate’ expressed in hertz, such as 60Hz, means.)

[Trivia from an old fart: the even older TVs which used vacuum tubes instead of transistors would not immediately lose their charges when you switched them off – instead they would discharge gradually. The TV image would shrink rapidly to a dot as the magnetic aiming plates zeroed out, but the dot might remain for quite a while as the electron gun kept firing off, exhausting the charges from the tubes – this might take several seconds to over a minute. Also, devices that used tubes always had a certain, ‘hot’ smell to them.]

A more noticeable delay is the re-emission of phosphorescence is most easily seen in glow-in-the-dark toys and such, which work just as well with UV light as with visible. I will swear that while watching the ornament seen above in the dark one (slow) night, I saw the light output suddenly ‘step’ downwards a fraction as if switched to a dimmer setting – how this could take place, and whether it was more an artifact of my eyes, is something I have yet to determine.

something small fluorescing under ultravioletAnyway, as I was typing all this I realized that I hadn’t tried out the UV light around the new yard yet. I had done a little exploring in different areas around the old place, finding very little of interest, but so far hadn’t checked out this area. I knew there were no scorpions to find, but what about other arthropods? Some macro photographers, like Nicky Bay, have discovered a lot of arthropods that fluoresce under UV, but these are mostly exotic (meaning, not found in North Carolina.) But I went out looking anyway.

I found a few bits of odd fabric, like an old tennis ball and a patch of threads in the garden – who knows where it came from? I was convinced that I had found a small patch of fluorescent fungus until I saw the details after downloading the images. But at left, a minuscule sphere of something that fluoresced as strongly as many synthetic materials, perched on a fencepost, a fraction of a millimeter across. I haven’t the faintest idea what this is, but the color in visible light put me in mind of tree resin, though I suppose it could also be an egg, or perhaps an alien artifact.

[Another short, nonsense diversion: I got into a discussion on a UFO blog once with someone who was using UV light to find evidence of alien visitation on people’s skin – four-fingered handprints, “ancient symbols,” and so on. It got especially entertaining when I challenged him to explain how, exactly, he considered these “alien” when we have countless substances that fluoresce under UV light, including things as benign and easy to obtain as highlighting fluid. He tried blathering about spectra to disguise the fact that he had no controls at all, and I was circumspect enough not to accuse him of planting the ‘evidence’ himself. But yeah, that’s how it goes in UFO and paranormal circles – we haven’t any evidence whatsoever of alien species, much less any traits we could be confident in, but glowing stuff magically appearing on someone’s skin under a black light must be aliens. Is it any wonder that I promote critical thinking?]

Apheloria virginiensis montana nymph in visble lightAt one point, I found the juvenile form of an Apheloria virginiensis montana, a large black & yellow centipede that’s not hard to find around here – see the adult here. About 3cm long and the color of dirt, I would easily have missed it without the UV light, and even then it didn’t fluoresce too strongly, but enough to notice, anyway. It was next to impossible to convince to hold still, so I had a bit of fun finding the exposure time that would halt its motion enough to be reasonably sharp, and then setting the ISO to maintain it and still get enough light from the UV flashlight to render a decent image. The image below is 1/50 second at f4, ISO 800, and took numerous attempts, also including bad focus and the little bugger sticking to the edges of the storage container I used as a restraint, not providing the best of backgrounds.

Apheloria virginiensis montana nymph under ultraviolet light

More interesting was the spined micrathena (Micrathena gracilis,) a common spider in the woods around here, notorious for spinning webs at face height between trees. It displayed some nice, distinctive fluorescing portions, notable in that they appear glossy black under visible light (yes, the spider was shifting position between the two images, and I just tried to match them as best I could for comparison – note the inverted branch.) The purpose of this fluorescence is unclear – I have yet to find any source that even admits it’s a property of the species – so to go the wild speculation route, it is possible that the peculiar shape and selective fluorescence mimics some plant species, luring insects to their doom. Several flowers have been found to have distinctive patterns in UV, and many species of pollinators can see this and use it to home in on good food sources. That’s about the best I can come up with, also helping to explain the elaborate shape of the abdomen, but it would be a lot more plausible if I had the faintest knowledge of any plant that appeared like this.

Micrathena gracilis in visible and ultraviolet light

The sun, as we know, puts out plenty of UV itself, and everything that fluoresces under my little flashlight is also fluorescing in full daylight. But as may be guessed from looking at these images, the amount of light emitted by fluorescence isn’t very much at all, requiring much longer exposure times than daylight or even deep shade (and of course, trying to convince a spider to hold absolutely still for that time.) In most cases the reflected portion of the visible spectrum simply overwhelms the fluoresced photons, with rare exceptions like ‘day-glow’ materials, which give the faintest hint of their properties in a peculiarly bright appearance – also highlighting fluid, as mentioned.

Perhaps the coolest effect was discovered by accident, when I forgot to shut the flash off after I set the long shutter speed necessary for the UV versions. The mixed lighting produced a nice contrast, so I experimented until I had the best ratio down, then combined them in an alternating gif (pronounced “gnaw”.) It makes it easier to compare the fluorescent regions.

Micrathena gracilis in visible and ultraviolet light

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