I spend a slightly unreasonable amount of time writing about light. Stars, auroras, the Sun, strange things happening in space, and then occasionally a plant or an animal that has apparently decided it would like to make some of its own. You'd think I'd eventually run out of things to be surprised by, but nature keeps being very unhelpful about that.
Bioluminescence gets me every time. A tiny organism produces a chemical reaction and suddenly there is visible light coming out of it. Meanwhile, I have several lamps in my house and still manage to walk into furniture when it's dark.
The gardening part of my brain is especially vulnerable to this subject. I've written about glowing plants before, and the idea of something alive quietly making light still feels like it wandered out of one of the fantasy books I read. Except we can study the chemistry, identify the genes and ask what that glow is actually doing for the organism.
That last question is where it gets really good. A firefly, a deep-sea fish and a glowing mushroom aren't all doing the same thing just because we think they look magical. Some are finding mates, some are hiding, some are hunting, and some are using light in ways we're still trying to understand.
So yes, the title has poetry in it, because I am still me. But the actual biology is strange enough that I don't think we need to decorate every sentence with a glowing metaphor to make it interesting.
What Bioluminescence Actually Means
Bioluminescence is light produced through a chemical reaction by a living organism. It's a form of chemiluminescence, with the biology doing the work. A glow stick uses chemistry too, but it doesn't need to eat, reproduce or get through a difficult afternoon in the ocean.
You will often see the process described using two terms: luciferin and luciferase. Luciferin is a name given to light-producing substrates, and luciferase refers to enzymes that help catalyze the reactions. Those names describe roles, rather than one identical pair of molecules shared by every creature that glows.
That difference matters. A firefly's light-making chemistry isn't simply a tiny copy of the chemistry in a glowing mushroom or a bacterium. Some systems also use specialized light-producing proteins and other arrangements, so the neat little diagram in an introductory explanation is a starting point rather than a universal instruction manual.
The reaction releases energy as light with relatively little heat. That is why people call it cold light, although the phrase shouldn't make us imagine the organism has become a little refrigerator. It means the glow isn't produced by heating something until it becomes incandescent, as happens in the filament of an old-fashioned light bulb.
Oxygen is involved in the familiar light-producing reactions, but oxygen isn't being transformed into a flame. There is no tiny fire burning inside a firefly. As someone who already finds ordinary insects startling when they fly near my face, I'm glad we can at least rule out that particular complication.
Glowing and Reflecting Light Are Different Tricks
This is one of those distinctions I find myself wanting to explain at a party, which is probably why I end up writing blog posts instead. An organism can look brilliantly colorful without producing its own light. The appearance alone doesn't tell us where the energy is coming from.
Fluorescence happens when a material absorbs incoming light and re-emits some of that energy at a different wavelength. It needs an excitation source. Bioluminescence gets its immediate light energy from a chemical reaction, so it doesn't require us to shine a light on the organism first.
Then there is iridescence, where structures interact with incoming light to create colors that change with viewing angle. The shimmering rainbow bands along a comb jelly's moving comb rows are a famous example. Many comb jellies can also produce bioluminescence, but the rainbow you see under bright lights isn't automatically that glow.
I love that one animal can make us sort through several different explanations before we've even reached the rest of its biology. Nature could have chosen one impressive visual effect, apparently, but that would've been too straightforward.
The Glowing Waves Are Full of Tiny Organisms
Those photographs of blue surf are some of the most convincing evidence that the ocean is operating with a completely different idea of normal. In many coastal displays, the light comes from bioluminescent dinoflagellates, tiny planktonic organisms in the water. When conditions allow large numbers to gather, a breaking wave can reveal a whole stretch of blue light.
Mechanical disturbance can trigger their flash. Moving water deforms the cells and starts a rapid chain of events that leads to light production. Researchers at Scripps have studied how those organisms respond to forces in the water, which is a wonderfully specific job to have: figuring out exactly how to annoy plankton into glowing.
That doesn't mean every dinoflagellate glows, or that every red tide produces beautiful blue waves at night. Different species have different capabilities, and even a familiar-looking bloom needs proper identification. The color of the water during the day doesn't give us the entire answer.
The flashes are generally understood in the context of defense. A burst of light may startle a grazer or help draw attention to whatever is disturbing the plankton. There is something fairly dramatic about being almost invisible and defending yourself by briefly announcing the problem to the surrounding neighborhood.
I would happily watch this for an unreasonable amount of time. I also don't want to confuse a gorgeous photograph with a promise about what a beach will look like on any given night. The species, concentration, darkness, water movement and camera exposure all affect the display we end up seeing.
Nor does glowing water automatically mean safe swimming water. Blooms can have different ecological and health consequences, so local guidance matters. Admiring a natural phenomenon and immediately deciding to climb into it don't have to be the same activity, however tempting the photograph looks.
Sometimes a Fish Carries the Light, but Bacteria Make It
Bioluminescence gets even stranger once you find out the glowing animal isn't always supplying all the chemistry itself. Some fish house light-producing bacteria in specialized organs. The animal provides a place to live and resources, and the bacteria provide the light.
Certain deep-sea anglerfish are a familiar example. Their luminous lure can attract prey in an environment where a small visible signal stands out against the darkness. We see a bizarre-looking fish with a lamp on its head; a hungry animal nearby may see something worth investigating, which is an unfortunate difference of opinion.
Other animals produce light through their own cells and chemistry rather than a bacterial partner. It is worth keeping that distinction in mind when we say an animal makes its own light. Biology is full of partnerships, and sometimes the apparent solo performance involves a whole collection of much smaller participants.
This is the sort of thing that makes my genetics background and my love of weird science collide. The effect we notice from the outside might be one bright point, while the explanation involves different organisms, specialized tissues and a relationship maintained over time. The more closely we look, the less simple it gets.
Light Can Help You Hide
Counterillumination might be my favorite trick in this entire subject, partly because it sounds like a terrible plan until you understand the viewpoint. If a predator is looking upward through dim water, an animal above it can appear as a dark silhouette against the faint light coming down from the surface. That silhouette gives away its position.
Some marine animals produce light on their undersides that helps match the light behind them. Reduce the contrast, and the outline becomes harder to pick out. The animal isn't becoming invisible in every direction; it is dealing with a particular lighting problem for an observer below.
Researchers studying bioluminescent sharks have examined how patterns of light-producing organs relate to depth and the surrounding light environment. It's an actual camouflage strategy, not simply an animal glowing because everything in the deep sea apparently has to look a little haunted.
The part I love is how thoroughly it overturns my first instinct. If I were trying not to be noticed, turning on a light wouldn't be my opening move. Apparently I need to think more carefully about who is looking and what the background looks like from where they're standing, or swimming in this case.
Fireflies Are Having a Conversation We Keep Interrupting
Fireflies are beetles, which is already a useful little correction to a name that makes them sound like something else entirely. In many species, adults use flashes as courtship signals. The timing and pattern can help individuals recognize an appropriate mate rather than simply responding to any passing light.
That turns a summer evening into a much more interesting place. What looks to us like scattered little sparks can be a set of signals with timing that matters to the animals using them. We don't understand the conversation just because we're standing in the middle of it admiring the view.
Not every firefly species communicates in the same way, and not all adults produce the familiar flashing displays. The broad category contains different behaviors and life histories. I think that makes them more interesting, even if it ruins the convenience of having one sentence that explains every firefly on Earth.
It also makes outdoor lighting worth thinking about. Artificial light can interfere with the signals of some species, and habitat loss and pesticide use add other pressures. I've written about disappearing fireflies because I don't want something so familiar to become one of those things we only talk about in the past tense.
My own gardening has made me more aware of how much is happening in a yard besides whatever I intended to grow. Some of it eats my tomatoes or steals my figs, which I remain deeply annoyed about. Some of it is a beetle quietly trying to find a mate while we illuminate the entire neighborhood like a shopping center.
A Mushroom Can Glow Too, Because Apparently Plants Weren't Enough
Fungi aren't plants, but I know exactly which part of my brain reacts when I see a glowing mushroom. It's the same part that wants unusual things growing around me and has to be reminded that my garden has a finite amount of space. Biology has done an excellent job of finding ways to distract me from that limitation.
Some fungi produce green bioluminescence in their fruiting bodies, their mycelium, or both, depending on the species. Glowing fungal growth on decaying wood is often called foxfire. The glow can be subtle, and photographs made with long exposures don't necessarily reproduce what you'd notice while walking past.
Scientists have tested whether the light can attract insects. In a 2015 study, researchers used illuminated acrylic mushroom models and found that the green-lit models attracted more insects than unlit ones under their experimental conditions. The findings supported the possibility that light could help certain fungi attract insects involved in moving spores.
That is a fascinating result, but it isn't proof that every glowing fungus uses light for exactly that purpose. Different species may have different ecological explanations, and researchers are still investigating what the glow does across the group. We can enjoy an explanation without pretending the same answer has been checked everywhere.
I'm especially fond of how the study was approached. Someone had to look at a glowing mushroom and decide the next sensible step was to build a fake one with a light inside and see who showed up. That is a research plan I would have been extremely interested in hearing about over dinner.
Evolution Didn't Settle on One Way to Glow
The light-producing systems found across bacteria, fungi and animals aren't one universal invention passed unchanged through everything alive. Bioluminescence has evolved independently in different lineages. Different chemistries and structures can end up solving some related problems in very different organisms.
It makes sense that light would be useful in more than one context. If you live somewhere dark, a controlled signal can help you find food or a mate, confuse an attacker, or change how visible you are. What works for a fish in dim water doesn't need to be the same system used by a beetle flying over grass.
The exact evolutionary history is more complicated than putting one confident count in a sentence and moving on. It depends on which groups we're studying and how well their relationships are understood. I'd rather keep the useful point clear: nature has arrived at the ability to produce light repeatedly, and the result isn't one single biological trick.
Yes, Scientists Have Made Glowing Plants
This is where my gardening attention span leaves the room entirely. In a 2020 Nature Biotechnology paper, researchers described tobacco plants engineered with genes from a fungal bioluminescence system. The plants could produce light visible to the naked eye without needing an externally supplied luciferin added each time.
The system connected fungal light-producing chemistry with caffeic acid, a compound already present in plants. That allowed the plants' metabolism to support the glow. It was a real genetic-engineering achievement, and it is one reason I keep returning to this subject after already writing about bioluminescent flora.
It doesn't mean ordinary garden plants naturally light up at night. It also doesn't mean a glowing plant is bright enough to replace a reading lamp or a streetlight. Seeing light after your eyes adjust to darkness and illuminating a sidewalk to a practical standard are very different assignments.
Still, come on. A living plant that glows is an extremely good way to get my attention, even if the sensible part of me wants to ask about brightness, growing conditions and how it was made. The science makes the idea more interesting to me, not less, because now I can start to understand what I'm actually looking at.
I already enjoy growing things that turn light into leaves and tomatoes. Finding out we can connect some of that chemistry to visible light production is wonderfully wierd. It doesn't need to solve every lighting problem in Philadelphia to deserve a little amazement.
The Glow Is Useful in a Laboratory Too
Light-producing systems have become valuable research tools because scientists can connect a measurable signal to a biological process they want to study. A luciferase reporter can help reveal activity in cells or track changes in an experiment. The meaning of the signal depends on how the experiment is designed, rather than a glow automatically proving one particular thing.
Fluorescent proteins are also widely used in research, but they're a different category from luciferase-based bioluminescent systems. Green fluorescent protein, or GFP, needs incoming excitation light to fluoresce. The distinction that sounded slightly fussy earlier suddenly matters a lot when somebody is designing an experiment.
That's one of the reasons I like following these subjects past the beautiful photographs. A creature's chemistry becomes something researchers can adapt, measure and use to ask a completely different question. We start with a glowing organism and end up with another way to study what cells are doing.
I don't need to pretend every application has already become a medical treatment or a battery-free lamp. The actual tools are impressive enough on their own. There is plenty happening between a promising idea and a product that works in everyday life, and that middle part is often where the most interesting science lives.
I Want to See It Without Getting in the Way
For fireflies, I like the idea of giving the evening a chance to be dark and watching without trying to turn it into a staged performance. Follow local habitat guidance, leave the animals where they are, and be thoughtful about lights. A glowing creature isn't asking to become a prop just because it makes an excellent photograph.
For glowing surf, I'd check local information and conditions rather than assume an old photograph predicts tonight's display. For mushrooms, I'd want a knowledgeable guide and accurate identification. A green glow is fascinating, but it isn't an invitation to eat whatever you found in the woods.
The same attention I bring to looking at the sky applies here. Put the phone down for a little while, give your eyes time to adjust and pay attention to the thing you're actually there to see. I realize that is ambitious advice from someone who then wants to write several thousand words about it, but I do think the looking part deserves its own time.
The Chemistry Doesn't Ruin It for Me
I don't look at a firefly and feel disappointed because there's an enzyme involved. I think it's ridiculous that a small beetle can do that at all, and then I want to know approximately everything about it. The explanation gives me more things to notice the next time I see one.
That is probably the thread connecting most of what I write: wine, plants, food, stars and the strange things happening in places I rarely get to see. Something ordinary catches my attention, I start reading, and suddenly the thing in front of me has become much bigger and more interesting than I expected.
Bioluminescence is a particularly beautiful version of that. There is actual chemistry producing actual light, used by living things trying to get through their own complicated little lives. I'm perfectly happy to find some poetry in it after I've taken a moment to appreciate how absurdly good the biology already is.
A jellyfish lamp would be extremely entertaining company while I write about this. Those little floating shapes, the colors, the excuse to watch something drift around instead of answering an email…yes, I can see myself getting attached.
Related Reads You Might Enjoy
When the Light Becomes Too Bright: How a Quasar Silenced the Sky
The Light That Shouldn’t Exist: Discovering Stars in the Darkest Corners
The Sun Isn’t Yellow: A Mind-Bending Dive into Light, Space, and the Lies Our Atmosphere Tells
How Do Auroras Form? A Dance of Solar Fire and Magnetic Veils
The Great Attractor: The Cosmic Force Pulling Us Through Space
When Plants Glow: The Science (and Magic) Behind Bioluminescent Flora
We Are Vessels of Light: How Sunlight Moves Through Us and Mends Our Vision
Works Cited
NOAA Ocean Exploration and the Deep Ocean Education Project. “Factsheet: Bioluminescence.”
Scripps Institution of Oceanography. “Research Highlight: The Force behind Nature’s Light.”
Scripps Institution of Oceanography. “Everything You Wanted to Know About Red Tides.”
MBARI. “Glow-in-the-dark corals light up the deep sea.” 2020.
