May 11, 2026 • 12 mins
When organisms like fireflies, fungi, and fish glow with cold light, there's chemistry at work. Learn what we know (and don't know!) about bioluminescence -- including how humans are harnessing it -- in this episode of BrainStuff, based on this article: https://animals.howstuffworks.com/animal-facts/bioluminescence.htm/printable
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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey Brainstuff Lauren
vogelbomb here. Animals that use their sense of sight to
navigate generally have a hard time getting around without light,
so there are a lot of adaptations out there to help.
For example, owls have very large, tubular eyes that they
(00:25):
use to collect a lot of light. Cats have a
layer of highly reflective material deep in their eyes to
give their light receptors a second chance at gathering it.
Humans have put a lot of effort into creating portable,
often artificial light sources, from torches to light bulbs and LEDs.
Some bioluminescent life forms have an entirely different approach. They
(00:49):
make their own light and carry it around in their bodies.
Some of these animals use the light they produce the
same way that people use flashlights or searchlights, but bioluminescent
animals produce light very differently from the way that traditional
light bulbs do. Traditional light bulbs and fires, for that matter,
(01:10):
create light through incandescence. A material like wood or a
filament inside a bulb gets very hot and emits light.
This process isn't particularly efficient, since generating enough heat to
create light wastes an enormous amount of energy. That's why
led light bulbs have become so popular. They use what's
(01:32):
called electroluminescence to basically use a low amount of electrical
current to produce photons. When that current is run through
certain semiconductive substances, it produces light but wastes a lot
less energy. In life forms that use luminescence, chemical compounds
mixed together to produce a glow. It's a lot like
(01:54):
the way that substances inside a light stick combine to
make light. Illuminescence of any kind is far more efficient
than incandescence. It neither requires nor generates much heat, so
it's sometimes known as cold light, hot or cold. A
light generally comes from one source, an excited electron. Basically,
(02:16):
energy causes an electron to move up a level in
its atomic orbit. When the electron settles back down, it
releases a photon, or a tiny packet of light. The
result in various life forms can be beautiful alike the
twinkling of fireflies, or a little eerie, like the glow
of foxfire. It can have all kinds of uses, from
(02:37):
protection to predation to we're not really sure what today,
let's talk about the basic process behind bioluminescence and how
different life forms use it to their advantage. You can
find bioluminescent life forms all over our planet. On land.
The aforementioned foxfire comes from glowing species of fungi that
(03:01):
feed on rotting wood, creating an ectoplasm green carpet of
light in Appalachian and other forests at night. In some
types of fungus, the whole structure glows, in others only parts,
like the aptly nicknamed jack o lantern, mushrooms, gills. Then
there are various land animals, including some insects, centipedes, millipedes,
(03:23):
and worms. You know fireflies and glowworms, which are the
larvae of various species of flies and beetles. But most
of the world's bioluminescence exists in the oceans, and particularly
in the depths known as the twilight zone. This has
nothing to do with rod sterling that I know of.
(03:44):
In this zone, which extends from about six hundred and
sixty to three thousand, three hundred feet which is two
hundred to one thousand meters, some light but very little
penetrates from the surface. The water above this zone absorbs
wavelengths red, orange, and yellow sunlight and scatters violet light,
so the light that reaches the twilight zone is bluish
(04:07):
green in color. At this depth you can find lots
of bioluminescent jellyfish, squid, shrimp, krill, marine worms, and fish.
Most make light that matches that blue green sunlight that
exists in this zone. The animal's glow can travel a
long way and it can blend in with the light above.
(04:28):
In some places, these animals, not the sun, are the
primary source of light, So that's weird. Next question, why
Hypothetically the evolution of something that requires a body to
use precious resources usually has a reason. Like I said
a minute ago, we don't know all of them yet.
(04:52):
For example, several species of earthworm secrete luminescent stuff that
doesn't have an obvious purpose. We think that some mushrooms
glow to attract insects to help spread the mushrooms spores.
But yeh, a few animals light up when nearby animals
start to glow, and there's not always a clear reason
(05:12):
for this behavior. One of my favorite examples is the
phenomenon known as the milky sea Awhere in the surface
of the ocean glows at night. Okay, so some species
of single celled plankton glow when they're disturbed. Tides, storms,
swimming marine life, and passing ships can cause large numbers
(05:32):
of these plankton to produce light simultaneously. In some cases,
this glow is so bright that it interferes with marine navigation.
There's a hypothesis that this works sort of like a
burglar alarm to help the population of plankton survive. The
idea goes that if a small fish begins to feed
on the plankton, the disturbed plankton emit a flash of light.
(05:57):
The light attracts larger fish, which are likely to be
the smaller fish as predators, and will thus prevent more
of the plankton from being eaten by eating those smaller fish. However,
this system doesn't seem to be as fool proof as
some of the better understood uses for bioluminescence. So what
do we know. We know that some animals use bioluminescence
(06:21):
for communication. Of Fireflies flash at one another in species
specific patterns, often in order to find a mate, but
attraction isn't always benevolent. In the twilight depths, of the ocean.
Some fish species, like the anglerfish, use aluminescent lure to
attract prey. Some twilight zone fish species use their luminescence
(06:43):
more like a spotlight to find prey. A one species
of loose jawfish produces red wavelengths of light because red
is uncommon at those depths, many deep water species didn't
evolve to see it, so we think the loose jaws
red light may allow it to spot and sneak up
on prey. Bioluminescence can also be used for camouflage and mimicry. Okay,
(07:07):
in the darker parts of the ocean, it's hard to
see anything below you, but easy to see the silhouette
of what's above you. For this reason, some species produce
spots of light on their undersides, which blur their outlines
and allow them to blend in with the light coming
from above. This is also known as counter illumination. Or
(07:28):
take for example, the cookie cutter shark, which has one
unlit patch on its underside, and that patch resembles a
smaller fish when viewed from below. Thus, a predator may
approach and this shark can take a bite out of
it and then flee which allows the cookie cutter shark
to prey on animals that are much larger and more powerful.
(07:49):
Bioluminescence can also be used for self defense when threatened.
Some animals release a cloud of bioluminescent fluid, similar to
the way that squid defend themselves with a cloud of anis.
Others use a bright flash to temporarily blind predators. But
okay I said earlier that bioluminescence comes from chemical reactions.
(08:11):
For all of these different uses of light in all
of these different organisms, the actual compounds at play can
be different, but the basic formula is the same. In general,
bioluminescence involves the combination of two types of substances in
a light producing reaction, a luciferin and a luciferase. Luciferns
(08:32):
are a category of light producing substances. Luciferases are a
category of enzymes that catalyze the reaction. Often the process
requires the presence of other substances, like oxygen or a
denticine triphosphate that's ATP, a molecule that stores and transports
energy in living cells. The luciferase basically allows the oxygen
(08:55):
or whatever to interact with the dormant luciferin, thus prompting
it to produce photons of light. The terms both come
from the Latin term lucifer which means light bringer. Lots
of different substances can act like luciferins and luciferases. For example,
those milky seed plankton obtain their energy through photosynthesis, and
(09:17):
they have a luciferin that resembles chlorophyll. Some shrimp and
fish appear to manufacture their lucifern from the food that
they eat, but not all bioluminescent life forms produce their
own light. Some animals create these substances in their own bodies,
but others have developed a symbiotic relationship with light producing bacteria.
(09:40):
These bacteria typically live in a specialized organ in the
host organism's body. The bacteria produce light all the time,
so in order to turn their lights on and off,
some animals can pull and push their light producing organs
into and out of their bodies. Others cover them with
membranes of skin to eyelids. Because of all of these
(10:03):
variations and how bioluminescence works, researchers think that this ability
to make light evolved independently in multiple forms of life,
and although humans didn't evolve by iluminescence, we've been using
it to our advantage for thousands of years. In ancient Rome,
plenty of the Elder wrote about using jellyfish goo to
(10:24):
paint a walking stick and making it into a cold torch.
People around the world have picked foxfire fungi to use
his lanterns, or cultivated them along pathways to light a trail.
During World War Two, the Japanese army harvested and dried
tiny bioluminescent crustaceans that, when crushed by soldiers in the field,
(10:45):
provided just enough light to say, read a map, without
giving their location away to any enemies nearby. Modern navies
track milky seed plankton to detect enemy movement, and researchers
can similarly track animals to learn more about them. Researchers
have even used luciferins and luciferases to help tag and
(11:08):
literally illuminate the workings of different cells and proteins in
order to better understand things like nerve damage in Alzheimer's
disease and the proliferation of cancers in living bodies. But
as I've said, we don't even understand everything there is
to know about these beautiful and useful biological processes. Hopefully
(11:31):
future research will help light the way to even more
applications a bioluminescence. Today's episode is based on the article
how bioluminescence works on how stuffworks dot com, written by
Tracy V. Wilson, who you may be familiar with from
a little show called Stuff You Missed in History class.
(11:52):
Brain Stuff is production of by Heart Radio in partnership
with how Stuffworks dot Com and is produced by Tyler Klang.
Four more podcasts my heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you listen to your favorite shows.
Welcome to Brainstuff, a production of iHeartRadio, Hey Brainstuff Lauren
vogelbomb here. Animals that use their sense of sight to
navigate generally have a hard time getting around without light,
so there are a lot of adaptations out there to help.
For example, owls have very large, tubular eyes that they
(00:25):
use to collect a lot of light. Cats have a
layer of highly reflective material deep in their eyes to
give their light receptors a second chance at gathering it.
Humans have put a lot of effort into creating portable,
often artificial light sources, from torches to light bulbs and LEDs.
Some bioluminescent life forms have an entirely different approach. They
(00:49):
make their own light and carry it around in their bodies.
Some of these animals use the light they produce the
same way that people use flashlights or searchlights, but bioluminescent
animals produce light very differently from the way that traditional
light bulbs do. Traditional light bulbs and fires, for that matter,
(01:10):
create light through incandescence. A material like wood or a
filament inside a bulb gets very hot and emits light.
This process isn't particularly efficient, since generating enough heat to
create light wastes an enormous amount of energy. That's why
led light bulbs have become so popular. They use what's
(01:32):
called electroluminescence to basically use a low amount of electrical
current to produce photons. When that current is run through
certain semiconductive substances, it produces light but wastes a lot
less energy. In life forms that use luminescence, chemical compounds
mixed together to produce a glow. It's a lot like
(01:54):
the way that substances inside a light stick combine to
make light. Illuminescence of any kind is far more efficient
than incandescence. It neither requires nor generates much heat, so
it's sometimes known as cold light, hot or cold. A
light generally comes from one source, an excited electron. Basically,
(02:16):
energy causes an electron to move up a level in
its atomic orbit. When the electron settles back down, it
releases a photon, or a tiny packet of light. The
result in various life forms can be beautiful alike the
twinkling of fireflies, or a little eerie, like the glow
of foxfire. It can have all kinds of uses, from
(02:37):
protection to predation to we're not really sure what today,
let's talk about the basic process behind bioluminescence and how
different life forms use it to their advantage. You can
find bioluminescent life forms all over our planet. On land.
The aforementioned foxfire comes from glowing species of fungi that
(03:01):
feed on rotting wood, creating an ectoplasm green carpet of
light in Appalachian and other forests at night. In some
types of fungus, the whole structure glows, in others only parts,
like the aptly nicknamed jack o lantern, mushrooms, gills. Then
there are various land animals, including some insects, centipedes, millipedes,
(03:23):
and worms. You know fireflies and glowworms, which are the
larvae of various species of flies and beetles. But most
of the world's bioluminescence exists in the oceans, and particularly
in the depths known as the twilight zone. This has
nothing to do with rod sterling that I know of.
(03:44):
In this zone, which extends from about six hundred and
sixty to three thousand, three hundred feet which is two
hundred to one thousand meters, some light but very little
penetrates from the surface. The water above this zone absorbs
wavelengths red, orange, and yellow sunlight and scatters violet light,
so the light that reaches the twilight zone is bluish
(04:07):
green in color. At this depth you can find lots
of bioluminescent jellyfish, squid, shrimp, krill, marine worms, and fish.
Most make light that matches that blue green sunlight that
exists in this zone. The animal's glow can travel a
long way and it can blend in with the light above.
(04:28):
In some places, these animals, not the sun, are the
primary source of light, So that's weird. Next question, why
Hypothetically the evolution of something that requires a body to
use precious resources usually has a reason. Like I said
a minute ago, we don't know all of them yet.
(04:52):
For example, several species of earthworm secrete luminescent stuff that
doesn't have an obvious purpose. We think that some mushrooms
glow to attract insects to help spread the mushrooms spores.
But yeh, a few animals light up when nearby animals
start to glow, and there's not always a clear reason
(05:12):
for this behavior. One of my favorite examples is the
phenomenon known as the milky sea Awhere in the surface
of the ocean glows at night. Okay, so some species
of single celled plankton glow when they're disturbed. Tides, storms,
swimming marine life, and passing ships can cause large numbers
(05:32):
of these plankton to produce light simultaneously. In some cases,
this glow is so bright that it interferes with marine navigation.
There's a hypothesis that this works sort of like a
burglar alarm to help the population of plankton survive. The
idea goes that if a small fish begins to feed
on the plankton, the disturbed plankton emit a flash of light.
(05:57):
The light attracts larger fish, which are likely to be
the smaller fish as predators, and will thus prevent more
of the plankton from being eaten by eating those smaller fish. However,
this system doesn't seem to be as fool proof as
some of the better understood uses for bioluminescence. So what
do we know. We know that some animals use bioluminescence
(06:21):
for communication. Of Fireflies flash at one another in species
specific patterns, often in order to find a mate, but
attraction isn't always benevolent. In the twilight depths, of the ocean.
Some fish species, like the anglerfish, use aluminescent lure to
attract prey. Some twilight zone fish species use their luminescence
(06:43):
more like a spotlight to find prey. A one species
of loose jawfish produces red wavelengths of light because red
is uncommon at those depths, many deep water species didn't
evolve to see it, so we think the loose jaws
red light may allow it to spot and sneak up
on prey. Bioluminescence can also be used for camouflage and mimicry. Okay,
(07:07):
in the darker parts of the ocean, it's hard to
see anything below you, but easy to see the silhouette
of what's above you. For this reason, some species produce
spots of light on their undersides, which blur their outlines
and allow them to blend in with the light coming
from above. This is also known as counter illumination. Or
(07:28):
take for example, the cookie cutter shark, which has one
unlit patch on its underside, and that patch resembles a
smaller fish when viewed from below. Thus, a predator may
approach and this shark can take a bite out of
it and then flee which allows the cookie cutter shark
to prey on animals that are much larger and more powerful.
(07:49):
Bioluminescence can also be used for self defense when threatened.
Some animals release a cloud of bioluminescent fluid, similar to
the way that squid defend themselves with a cloud of anis.
Others use a bright flash to temporarily blind predators. But
okay I said earlier that bioluminescence comes from chemical reactions.
(08:11):
For all of these different uses of light in all
of these different organisms, the actual compounds at play can
be different, but the basic formula is the same. In general,
bioluminescence involves the combination of two types of substances in
a light producing reaction, a luciferin and a luciferase. Luciferns
(08:32):
are a category of light producing substances. Luciferases are a
category of enzymes that catalyze the reaction. Often the process
requires the presence of other substances, like oxygen or a
denticine triphosphate that's ATP, a molecule that stores and transports
energy in living cells. The luciferase basically allows the oxygen
(08:55):
or whatever to interact with the dormant luciferin, thus prompting
it to produce photons of light. The terms both come
from the Latin term lucifer which means light bringer. Lots
of different substances can act like luciferins and luciferases. For example,
those milky seed plankton obtain their energy through photosynthesis, and
(09:17):
they have a luciferin that resembles chlorophyll. Some shrimp and
fish appear to manufacture their lucifern from the food that
they eat, but not all bioluminescent life forms produce their
own light. Some animals create these substances in their own bodies,
but others have developed a symbiotic relationship with light producing bacteria.
(09:40):
These bacteria typically live in a specialized organ in the
host organism's body. The bacteria produce light all the time,
so in order to turn their lights on and off,
some animals can pull and push their light producing organs
into and out of their bodies. Others cover them with
membranes of skin to eyelids. Because of all of these
(10:03):
variations and how bioluminescence works, researchers think that this ability
to make light evolved independently in multiple forms of life,
and although humans didn't evolve by iluminescence, we've been using
it to our advantage for thousands of years. In ancient Rome,
plenty of the Elder wrote about using jellyfish goo to
(10:24):
paint a walking stick and making it into a cold torch.
People around the world have picked foxfire fungi to use
his lanterns, or cultivated them along pathways to light a trail.
During World War Two, the Japanese army harvested and dried
tiny bioluminescent crustaceans that, when crushed by soldiers in the field,
(10:45):
provided just enough light to say, read a map, without
giving their location away to any enemies nearby. Modern navies
track milky seed plankton to detect enemy movement, and researchers
can similarly track animals to learn more about them. Researchers
have even used luciferins and luciferases to help tag and
(11:08):
literally illuminate the workings of different cells and proteins in
order to better understand things like nerve damage in Alzheimer's
disease and the proliferation of cancers in living bodies. But
as I've said, we don't even understand everything there is
to know about these beautiful and useful biological processes. Hopefully
(11:31):
future research will help light the way to even more
applications a bioluminescence. Today's episode is based on the article
how bioluminescence works on how stuffworks dot com, written by
Tracy V. Wilson, who you may be familiar with from
a little show called Stuff You Missed in History class.
(11:52):
Brain Stuff is production of by Heart Radio in partnership
with how Stuffworks dot Com and is produced by Tyler Klang.
Four more podcasts my heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you listen to your favorite shows.
BrainStuff News
Host
Lauren Vogelbaum
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