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Floral Fluorescence

Medicinal Plants in a New, Ultraviolet Light


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Like something from the 1940 film “Fantasia” or the 2009 film “Avatar,” San Gabriel, California-based photographer Craig Burrows uses a technique called ultraviolet-induced visible fluorescence (UVIVF) photography to capture the beauty, diversity, and morphology of plants, including medicinal plants, in a way they are not normally seen. This involves using an ultraviolet (UV) light source, which makes the plants fluoresce in spectacular and unpredictable displays. Humans do not see the UV light, however — just the plants’ reactions to it.1,2

Think of how a black light, which emits invisible UV light, causes a white T-shirt to glow blue or violet. And, under UV light, tonic water fluoresces bright blue due to the presence of the antimalarial compound quinine (from Cinchona spp., Rubiaceae).3

Burrows, who has been interested in nature from an early age but never formally studied botany, started using this technique in 2013 or 2014, just a few years after he started photography in general. “I saw somebody else doing it, I thought it was a really cool-looking technique, and I wanted to try it myself,” he said (oral communication, January 10, 2022).

The process requires total darkness. Burrows uses a 365-nanometer UV light source with 12 light-emitting diodes (LEDs) arranged in a small square. He typically uses a 10-second camera exposure, with the camera on a tripod, and moves the light source around the subject during the exposure time. This creates a “light painting” effect and avoids sharp shadows.

“One thing that I like to convey as much as possible with this is that the luminescence is not coming from an external source,” Burrows said. “It is actually being emitted from the subject. I want to emphasize that characteristic visually as much as possible by smoothing out the light source.”

UV light has wavelengths that are shorter than visible light but longer than X-rays. Fluorescence, a type of luminescence, occurs when a substance absorbs light of one wavelength and almost immediately reradiates light, usually of a longer wavelength. This happens when electrons of the fluorescent substance move to a high-energy state. From this excited, unstable state, they then lose energy in the form of heat and visible light while returning to their “normal” energy state.4

Fluorescence ceases nearly immediately when the exciting source is removed, unlike phosphorescence, which continues as an afterglow. Because humans generally cannot see UV light, except in rare cases,* fluorescent objects appear to glow mysteriously on their own when illuminated by UV light in a dark room.4 High-quality UVIVF photography actually rejects as much UV light as possible from the camera’s sensor and instead captures the visible light radiated from the subject.7

When a fluorescent object is illuminated by both UV light and visible light (such as sunlight), the visible light created by the object’s fluorescence is added to the visible light reflecting off the object, so a fluorescent object under full illumination appears to be unusually bright but not glowing on its own, as with UV light only.4

To get started with UVIVF photography, Burrows said some results can be achieved almost immediately with a high-quality UV light. He has coached people on using the technique and helps troubleshoot if, for example, their photos have blue speckles everywhere or are entirely purple.

“You can do this without a lot of skill or technology,” he said. “But, to get to a point where it is true to the subject matter but also is portrayed in an aesthetically pleasant way, I do think that requires a good deal of skill to get to that level.”

Burrows uses a Sony A99 camera, which is not modified in any way, and a simple macro lens. So, the effect is achieved entirely with the UV light source, he said. The subject is usually on a black stool with a black backdrop, if he doesn’t have a lot of space, since the best way to achieve a black background is to have a lot of space between the subject and what is behind it.

Because the technique requires such long exposure times, even a slight breeze, especially with a high-magnification image, will make it blurry, so most of Burrows’ UVIVF photos are taken inside. “I am very much a pixel peeper,” he said. “I’m very particular about how sharp the image is. I try to keep it as controlled as possible. So, usually, I do these in my garage, and I actually grow the plants myself as much as possible, or I’ll find them in the neighborhood or somewhere where I can take a cutting without being too impactful.”

The exposure time is one limitation of the technique. “I’m using a fairly intense light source, but I still need a long exposure for it,” Burrows said. “I would say that’s a drawback. You can’t have a high-quality image and also have a fast-captured image. And, of course, there’s a little bit of hazardousness with ultraviolet in general. So, that’s not ideal.”

On the other hand, Burrows believes the technique can stimulate people’s interest in botany. “If you photograph the same thing in ultraviolet, there is a sense of wonder that isn’t normally there,” he said. “In the same way it made me more interested in plants, I hope it can make other people interested.”

He said the technique involves trial and error. “It took me maybe an embarrassingly long time to realize that my shots were blurry not because I was moving the camera…, but because the subjects themselves were actually moving,” he said.

He found the anthers of some flowers wiggle around during the exposure, and some plants, including species in the Malvaceae family, close up at certain times of day. Burrows counteracts these challenges in different ways. For example, when he went to Hawaii to photograph plants for Hana Hou! magazine, he initially was frustrated when taking photos of Boerhavia repens (Nyctaginaceae), because the plant closed up at night. However, it was open the next day, so he got the shot he wanted then.

In another case, the California poppy (Eschscholzia californica, Papaveraceae) is open only during the day, he said, but he wanted it to open at night, so he put it in a vase and trained it to be 12 hours off. “So, sometimes there’s a little trickery, and sometimes you just work with what you have,” he said.

Two of Burrows’ favorite plants that he has photographed with UVIVF are lacy phacelia (Phacelia tanacetifolia, Boraginaceae) and largeflower phacelia (Phacelia grandiflora). “Both produced these really good mixes of colors, with some oranges, greens, purples, and reds, and they are very radiant-looking and sort of warm and inviting,” he said.

On the other hand, Burrows can think of two plants that were particularly difficult. One was bird’s eyes (Gilia tricolor, Polemoniaceae), which is a California annual plant. The flowers move more than almost anything he has photographed. “All of my shots that I did, they were just curling up,” he said. The other was Massonia hirsuta (Asparagaceae), which is a South African plant. Because of how the flowers are positioned in the leaves, the dirt is visible, and if the leaves have water spots or dust, it can’t be removed because the leaves are hairy, he said. “Those two gave me so much trouble that I actually scrapped all the photos.”

Burrows said he thinks this technique is not more widely or commonly used maybe partly because it is challenging and some people may not have the patience for it. “There are some plants that just sort of flop with this technique,” he said. “They’re not beautiful, or they’re not very fluorescent. So, I think there’s a lack of immediate reward for it.”

He noted that good-quality short-wavelength light sources have become much less expensive and more accessible for the average person over the past 20 or 30 years. The UV light he recommends to beginners costs around $25, for example. So, a heyday for this may be arriving, he said.

The technique can also effectively be used to photograph scorpions and other arthropods. Burrows took his light to the redwood forest closest to him, Big Basin Redwoods State Park in California. “I found the entire floor was covered in millipedes — hundreds of intensely fluorescent millipedes,” he said.

Some species may derive evolutionary benefits from exhibiting fluorescence. For example, one study found that the Venus flytrap (Dionaea muscipula, Droseraceae) and other carnivorous plants, including pitcher plants in the genus Nepenthes (Nepenthaceae), fluoresce under UV light. The study authors proposed this fluorescence can help attract arthropods and other potential prey to the traps.8 Some species may also be fluorescent to attract pollinators, which can see UV light, but there is likely little similarity between UVIVF photography and the way bees, butterflies, and other pollinators see plants.7

Beyond plants, UVIVF has many practical applications in diverse areas. In microscopy, UVIVF is used to label proteins and analyze tissues, cells, and cellular structures.9 In forensics, it is used to identify and evaluate fibers, gunshot residue, biological fluids, fingerprints, and more.10 Recent research shows that UVIVF can provide valuable information about the pigmentation of feathers (which are found in many collections of Indigenous art) and may help identify the birds from which the feathers originated.11 Banknotes, postage stamps, and credit cards often have fluorescent security features to prevent fraud. In geology, fluorescence can be used to identify minerals, determine their locality, and differentiate between natural and synthetic gemstones.12 NASA’s Perseverance rover also has a UV laser to aid understanding of the environment on Mars.13

Burrows has tried UVIVF on almost everything he can think of: June bugs and other insects, some minerals, spiders, spider webs, tree bark, and lichens, for example.

He still wants to use the technique to photograph silversword plants (Argyroxiphium spp., Asteraceae), which are threatened shrubs that are endemic to Hawaii and grow on the slopes of Haleakalā volcano on Maui. “I think that is the highest on my list, but also one of the least attainable ones,” Burrows said.

For Burrows, using UVIVF has created opportunities that he would not have had otherwise, including getting to travel to Hawaii. He also was invited to the Azores, a Portuguese archipelago in the North Atlantic, to photograph the flora there with UVIVF, but that did not happen because of the COVID-19 pandemic. National Geographic and other publications have featured his work,2 and he was invited to exhibit some of his work at the Museum of Contemporary Art (MOCA) in Taipei, Taiwan.

The results of UVIVF still sometimes surprise Burrows. “That is kind of what keeps me going,” he said. “I have some educated guesses after doing it for so long. A white petal is probably going to either be blue or pink. It’s not going to be yellow or green or something like that…. I think there is always something new to stumble across.”

Burrows said he will continue to use UVIVF photography to capture the beauty of plants. “One reason I keep acquiring new plants is so I’ll have new subjects,” he said. “It’s definitely not because I have an addiction to buying new plants or anything like that.”

More of his work can be seen on his website at


The author would like to thank Craig Burrows, the late botanist and photographer Steven Foster, and HerbalGram Art Director Matthew Magruder for their help with this article.


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