hey you look purple I guess I should
come clean can you smile for me eating
my two front teeth are fake oh my god
they're purple and fake teeth look
different than real teeth in the
ultraviolet that's crazy
[Music]
[Applause]
[Music]
at first glance the world through a UV
camera looks like a black-and-white
version of the normal visible light
world I mean these white flowers are
white and UV this black towel still
black in UV and this makes a lot of
sense because ultraviolet light is very
similar to visible light I mean it's
right beside it on the electromagnetic
spectrum the wavelengths are just a
little shorter the energy per photon a
little higher so I would expect as my
first order assumption that all matter
should interact roughly the same way
with ultraviolet light as it does with
visible light but once you take a closer
look you find that the world in UV is so
much stranger and more wonderful than
you could have imagined for example it
looks a lot hazy er visibility is
reduced and clouds kind of blend in with
the sky it's like there's this fog
everywhere so why is this I want you to
try to work it out before I explain it
at the end of this video now take a look
at these glasses in the visible part of
the spectrum they are transparent they
look like regular lenses but in the UV
they are almost black they're absorbing
so much ultraviolet light now take a
look at this filter in the visible it
looks black but now in the ultraviolet
it looks transparent or at least
translucent this is a UV pass filter
it's absorbing all the visible light and
allowing the UV to pass through it these
two objects flip my intuitions about the
world on their head then you come to
something like this in one of these
bottles is soda water and in the other
is tonic water can you tell which is
which it's pretty hard to tell just
using visible light but in the
ultraviolet it's obvious this one looks
like Cola so why is that well it's
because
[Laughter]
there are some molecules in here that
interact with ultraviolet light
differently than ordinary water to
really see what's going on we've got to
take this inside same bottles
ultraviolet lamp when I turn it on it's
the tonic water that is bright whereas
outside it was dark how does this make
any sense well the thing is tonic water
contains the quinine molecule which was
originally a preventive medicine against
malaria but it tasted so bitter that
people mixed it with sugar water and
made a tonic
now some people quite liked that tonic
but the thing about the quinine molecule
is that it flores's meaning that it
absorbs ultraviolet light and reradiates
it as visible light and that's why in
here it looks like it's glowing but
outside what we're looking at it in the
ultraviolet it looks dark because it is
absorbing that ultraviolet energy and
there are some other products that have
fluorescent molecules in them often
laundry detergents so I'm gonna try this
one out does it look any different face
basically look the same one of the ideas
with laundry detergent is to make things
look really bright really white by
absorbing wavelengths that you can't see
like ultraviolet and then re radiating
them in the visible part of the spectrum
which in fact makes them look much
darker in the ultraviolet because they
are absorbing that energy to re radiate
it in the visible now if you're trying
to find things that look different in
ultraviolet light as opposed to visible
light
well flowers are a really good place to
start because bees and other insects can
see ultraviolet light and so plants have
a reason to evolve pigments that they
can see looking at these sunflowers you
can see on the inner parts of the petals
there's actually this really dark
pigment in the ultraviolet it's almost
black but you can't tell that at all
just looking with your eyes the way
these pigments work is that they are
molecules that have energy transitions
which correspond to the energy of an
ultraviolet photon so a UV photon comes
in hits an electron and excites it up to
a higher energy level and then the
electron can actually die excite in
these molecules by transferring its
energy to the
molecule to the bonds in that molecule
causing them to bend and vibrate and
stretch so effectively it's transferring
the UV energy into thermal energy and
ultimately to heat our skin has
molecules that do the same thing
specifically melanin and I'm bringing in
Diana the physics girl who has been
filming this video with me because she
knows a lot about melanin oh yeah
because I'm so tan right so your your
body wants to protect itself against UV
rays and so there's some cells in your
skin called melanocytes that produce
more melanin when UV rays hit your skin
and that melanin absorbs a lot of
visible light so it looks darker in the
visible which is why when you have more
melanin you look more tin exactly
melanin actually absorbs even better in
the ultraviolet part of the spectrum
that's where its peak is and so our skin
looks darker in the ultraviolet camera
than it does in the regular visible
camera yeah what I find so amazing is
that these melanin molecules are
transported inside the cell to the
nucleus forming this protective cap over
the place where the DNA is stored and
that way they prevent ultraviolet light
from penetrating into the nucleus and
causing damage to the DNA but you know
one thing I think was really interesting
looking at your face in the UV how do I
put this I mean your skin is so clear
and beautiful the visible part inspector
yeah bring it on so what is surprising
is how you can see a lot more contrast
maybe some freckles that I didn't even
know we're there it is surprising no but
it's true i I mean I noticed that on
yours as well think there's a bit around
your eyes there are spots
I can't notice just looking at you in
the visible spectrum and then and then
they pop right out when you're looking
through a UV camera and you know some
animals that also absorb UV I don't harp
seal pups so in the Arctic when they're
very specific it is but when they're
trying to do aerial surveys and take
photographs of colonies of seals it's
pretty easy to spot the adults because
they are dark colored but the pups
I guess being young and defenseless they
have a kind of camouflage their fur is
white in the biz
part of the spectrum and so they kind of
blend into the ice and snow but in the
ultraviolet part they are absorbing a
lot of that radiation
I think the ingenious thing about this
is it allows us to get an accurate count
of harp seals right because we can count
the pups to by taking photos in the
ultraviolet so this is actually one of
the uses of ultraviolet photography you
can also look for arctic foxes or polar
bears
using the same technique because they to
absorb ultraviolet and that makes so
much sense because these ultraviolet
rays have high enough energy that they
can do damage to your DNA and cause
cancers and other diseases so what
should you do if you are in an
environment with a lot of Sun as we are
but maybe you are not evolved for this
kind of climate yeah I would say if you
can't find some shade put on sunscreen
it's kind of like putting melanin over
the top of your skin yeah I mean the the
active ingredients in sunscreen aren't
melanin but they do effectively the same
thing they take ultraviolet light and
they convert it into thermal energy into
heat right right I mean a lot a lot of
ingredients in sunscreens some actually
reflect ultraviolet as well but a lot of
active ingredients in sunscreen absorb
ultraviolet light and change it into
heat this is what it looks like if you
don't go outside in the Sun very much I
just use sunscreen is that right is that
right well not every day but I remember
my mom was like you sounds green I'm
like okay so why does the world look so
hazy in the ultraviolet my first thought
was that it must be something in the
atmosphere that is absorbing the
ultraviolet light like pollution or just
one of the components of our atmosphere
but as physics girl pointed out to me if
things were really absorbing ultraviolet
light well the sky we look darker not
light not foggy like it does and of
course if you do look at the absorption
spectra of the common atmospheric
molecules you'll find that virtually
nothing absorbs in the UV so what is
going on well the answer is Rayleigh
scattering the same phenomenon that
makes our sky blue is responsible for
the reduced visibility this foggy hazy
appearance in the UV the shorter the
wavelength of light the more likely it
is to bow
soft tiny molecules in our atmosphere
and scatter in all directions so when we
look up we are actually seeing a blue
haze blocking out space it's a really
cool way of thinking about the blue sky
rally scattering is inversely
proportional to the wavelength of light
to the power of four so it really
strongly increases this shorter the
wavelength becomes in fact there's about
five times as much scattering of
ultraviolet light than there is a
visible light in the middle of the
spectrum so you know if we could see
ultraviolet light we might look up and
ask not why is the sky blue but why is
the sky ultraviolet and this is I think
the amazing thing about seeing in the
ultraviolet it's that it shows us how
the world is not how we perceive it to
be there's so much more going on there
than we would ever imagined oh my gosh
oh that's very interesting you know I
want more of this you know it's one
thing to know the way the world works
but it's another to see it so you're
doing a video on different SPFs and all
the sunscreen controversies on your
channel yes I'm talking about whether
SPF sunscreen look different with a UV
camera why SPF labeling is so weird and
why the FDA has proposed rules years ago
we still have figured out how to label
sunscreens it is contra yeah awesome so
I'll put a link to Diana's video you
should go check it out also the how to
make everything guys have made sunscreen
they've made sunscreen I haven't seen it
yet but I will put a link to their video
so you can go check that out as well why
is this fly only attacking me cuz I'm
wearing sunscreen it likes the smelly oh
yeah