Light sucking flames look like magic

Steve Mould
27 May 202418:04

Summary

TLDRThis video explores the science behind creating a black flame illusion using sodium streetlights and a methanol fire. It delves into the principles of light emission and absorption, explaining how sodium's unique spectral lines create the effect. The video also investigates special glasses used by glassblowers to filter out intense orange light and examines EnChroma glasses, which claim to enhance color vision for the colorblind. The script concludes with a historical note on Bunsen burners and their role in spectroscopy, adding an educational twist to the fascinating demonstration.

Takeaways

  • 🔥 The video demonstrates how to create a black flame using sodium streetlights, which emit a specific yellow-orange light.
  • 📞 The black and white footage is a trick to highlight the flame's color, as turning off auto white balance reveals the scene's yellow hue due to sodium lighting.
  • 💡 Sodium streetlights are efficient but have a Color Rendering Index (CRI) of zero, making them poor at showing colors naturally.
  • ⚛ The color of light emitted by an element like sodium is due to a specific electron transition, emitting photons with a fixed energy level.
  • 🌈 The video uses a diffraction grating to show the discrete spectral lines of elements like xenon, contrasting with sodium's single line.
  • 🔮 Sodium's single emission line also means it has a specific absorption spectrum, which is key to the black flame phenomenon.
  • 🔥 The black flame effect occurs because the flame absorbs the yellow-orange photons from the sodium streetlight, making it appear dark.
  • 👓 Glassblowers wear special glasses with neodymium and praseodymium to filter out the orange light emitted by sodium in glass, aiding visibility.
  • 👓 EnChroma glasses claim to help red-green colorblindness by filtering specific wavelengths, but their effectiveness is debated.
  • 🔬 The video uses a homemade spectrometer to analyze light spectra, showing the absorption lines of different elements.
  • 🔬 Bunsen burners were designed to provide a flame with minimal light for spectroscopy, aiding in the discovery of new elements.

Q & A

  • What is the main subject of the video?

    -The main subject of the video is to demonstrate how to create a black flame using sodium streetlights and explain the science behind it.

  • Why does the video mention glassblowers?

    -The video mentions glassblowers to introduce the concept of special glasses they use that can make fire appear invisible, which is related to the absorption of specific light wavelengths.

  • What is the significance of sodium streetlights in the black flame effect?

    -Sodium streetlights are significant because they emit light primarily at a wavelength of 590 nanometers, which is in the yellow-orange spectrum. This specific wavelength is absorbed by sodium atoms in the flame, causing it to appear black.

  • What is the role of the CRI in lighting?

    -The Color Rendering Index (CRI) measures how accurately a light source can reveal the true colors of objects in comparison to a natural light source like sunlight, which has a CRI of 100.

  • How does the video explain the color of a photon?

    -The video explains that the color of a photon is determined by its energy, which is the difference between two energy levels of an electron when it transitions between orbitals.

  • What is the purpose of the diffraction grating used in the video?

    -The diffraction grating is used to split light into its component colors, similar to how a prism works, to demonstrate the emission spectrum of different elements like xenon and sodium.

  • Why does the video discuss the absorption spectrum of sodium?

    -The absorption spectrum of sodium is discussed to explain how sodium atoms can absorb photons of a specific energy, which is crucial to understanding why the flame appears black under sodium streetlight illumination.

  • What is the explanation for the black flame appearing black despite the flame producing its own light?

    -The black flame appears black because the sodium streetlight is much brighter than the flame itself, and the light produced by the flame is negligible. Additionally, the photons emitted by the flame are scattered in random directions, with a low chance of reaching the observer's eyes.

  • What special glasses do glassblowers wear and why?

    -Glassblowers wear special glasses that contain neodymium and praseodymium, which absorb the orange light emitted by sodium, allowing them to see through the bright glare caused by the heated glass.

  • What is the video's take on EnChroma glasses and their effectiveness?

    -The video suggests that EnChroma glasses do what they claim in terms of filtering out specific light wavelengths, but whether they actually help colorblind people see colors they couldn't before is a topic of debate and not conclusively supported by the literature.

  • What is the historical significance of the Bunsen burner mentioned in the video?

    -The historical significance of the Bunsen burner is that it was designed to mix oxygen into the gas supply before ignition, creating a flame with minimal light of its own, which was crucial for spectroscopy and the discovery of new elements.

Outlines

00:00

🔥 The Mystery of the Black Flame

This paragraph introduces the concept of creating a black flame without any trick photography. It explains the role of sodium streetlights, which emit a yellow-orange light with a low Color Rendering Index (CRI) of zero, in creating the black flame effect. The video discusses the physics behind light emission and absorption, focusing on sodium's single visible light emission at 590 nanometers. It also touches on the idea of using heat to excite sodium atoms, as opposed to electricity, to produce light. The paragraph sets up the experiment of creating a black flame using a methanol fire and salt water, which releases and excites sodium, creating an orange flame. The key to the black flame effect is the absorption of the orange light by ground-state sodium atoms in the flame, which makes the flame appear dark under the specific lighting conditions.

05:02

🕶 Glassblower's Secret to Seeing Through Fire

The second paragraph delves into the science behind the black flame effect, addressing questions about the balance between light absorption and emission by the flame. It explains how the brightness of the sodium streetlight compared to the flame's own light production plays a crucial role. The paragraph also explores the concept of light scattering and absorption, using the example of a wall behind the flame. The discussion then shifts to glassblowers' special glasses that block the orange light emitted by sodium in glass when heated. The video mentions a visit to a glassblower and the use of a spectrometer to analyze light. It humorously introduces 'EnMouldia glasses' as a product to block the sodium streetlight's orange glow, segueing into a sponsorship mention of Odoo, an all-in-one management software for entrepreneurs, which offers free website and e-commerce solutions.

10:03

👓 The Science of Color Perception and EnChroma Glasses

This paragraph investigates the effectiveness of EnChroma glasses, which claim to enhance color vision for people with red-green colorblindness. It describes the use of a spectrometer to analyze the impact of EnChroma glasses on the light spectrum. The summary explains the common type of colorblindness related to overlapping sensitivity of red and green cones and how EnChroma glasses aim to address this by filtering out specific wavelengths. The paragraph also discusses the controversial marketing practices of EnChroma and the mixed literature on the effectiveness of their glasses. It concludes by suggesting that the value of EnChroma glasses may be subjective, depending on individual experiences and perceptions of color enhancement.

15:04

🔬 The Legacy of Bunsen Burners in Spectroscopy

The final paragraph wraps up the video with a historical note on Bunsen burners and their significance in spectroscopy. It explains that Robert Bunsen, known for the Bunsen burner, used this tool to heat elements with minimal light emission, which was essential for conducting spectroscopic experiments. The paragraph highlights the design feature of the Bunsen burner that allows for the mixing of oxygen into the gas supply, a critical component for the discovery of new elements. The video ends on a light-hearted note, suggesting that the information shared is a 'cool fact' about Bunsen burners.

Mindmap

Keywords

💡Black Flame

A black flame, as discussed in the video, is a phenomenon where a flame appears black due to the absorption of specific wavelengths of light. This occurs when the flame is exposed to a light source, like a sodium streetlight, which emits light at the same wavelength that the sodium atoms in the flame absorb. The flame itself does not emit enough light to counteract the absorption, resulting in a black appearance. This is a central concept in the video, demonstrating the interaction between light and matter at a quantum level.

💡Sodium Streetlight

Sodium streetlights are a type of lighting that uses sodium vapor to produce light. They are known for their efficiency but also for casting an orange-yellow hue that can distort the perception of colors. In the video, the sodium streetlight is used to create a scenario where the flame appears black because it emits light at the same wavelength that sodium atoms absorb. The script explains how sodium streetlights have a Color Rendering Index (CRI) of zero, meaning they do not support the natural appearance of colors.

💡Color Rendering Index (CRI)

The Color Rendering Index (CRI) is a measure of a light source's ability to reveal the true colors of objects in comparison to a natural light source. The CRI scale ranges from 0 to 100, with 100 being the closest to natural sunlight. In the video, it is mentioned that sodium streetlights have a CRI of zero, indicating they are very poor at rendering colors accurately, which ties into the demonstration of the black flame effect.

💡Electron Transitions

Electron transitions refer to the movement of electrons between different energy levels within an atom. When an electron jumps to a higher energy level, it absorbs energy, and when it falls back to a lower level, it emits a photon of light. The energy of the emitted photon corresponds to the difference in energy levels, determining the color of the light. In the context of the video, the electron transitions in sodium atoms are responsible for the characteristic yellow-orange color of light emitted by sodium streetlights.

💡Diffraction Grating

A diffraction grating is an optical component with a series of closely spaced lines or grooves that can split light into its component colors, similar to a prism. In the video, the diffraction grating is used to analyze the light emitted by different gases, such as xenon, and to demonstrate the discrete spectral lines characteristic of each element. This tool helps illustrate the concept of emission spectra and how they can be used to identify elements.

💡Emission and Absorption Spectra

Emission spectra and absorption spectra are two related concepts in atomic physics. An emission spectrum is the range of wavelengths emitted by an atom when an electron drops from a higher to a lower energy level. Conversely, an absorption spectrum is the range of wavelengths that an atom can absorb, causing an electron to move to a higher energy level. The video uses these concepts to explain how the black flame appears when sodium atoms in the flame absorb the orange light emitted by a sodium streetlight.

💡Methanol Flame

A methanol flame is produced by burning methanol, an alcohol that burns with a relatively clean and almost invisible flame. In the video, a methanol flame is used as a heat source to vaporize and excite sodium atoms from saltwater, leading to the emission of orange light. The script mentions the use of methanol for its nearly invisible flame, which is ideal for demonstrating the effect of sodium atoms on the flame's color.

💡Glassblower Glasses

Glassblower glasses are a special type of eyewear used by glassblowers to filter out the intense orange light emitted by heated glass containing sodium. The video demonstrates how these glasses, which contain neodymium and praseodymium, can block the specific wavelength of light emitted by sodium, allowing glassblowers to see their work more clearly. This concept is related to the black flame experiment, as it involves the absorption of specific light wavelengths.

💡EnChroma Glasses

EnChroma glasses are a type of eyewear designed to improve color perception for individuals with color vision deficiencies, particularly red-green colorblindness. The video discusses the technology behind these glasses, which involves filtering out specific wavelengths of light to reduce overlap in the sensitivity of red and green cones in the eye. The script explores the claims made by EnChroma and provides a critical perspective on their effectiveness.

💡Spectrometer

A spectrometer is a scientific instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically to identify substances through their emission or absorption spectra. In the video, a homemade spectrometer made from a modified webcam is used to analyze the light emitted by different light sources and to test the claims of EnChroma glasses. This device helps visualize the specific wavelengths of light that are absorbed or transmitted through various materials.

💡Bunsen Burner

A Bunsen burner is a type of laboratory burner providing a single, flat flame, which is used for heating, sterilization, and combustion. Named after the German chemist Robert Bunsen, it was designed to produce a flame with minimal light emission, which is ideal for spectroscopic experiments. The video script mentions the Bunsen burner in the context of spectroscopy and the discovery of new elements, highlighting its historical significance in scientific research.

Highlights

Demonstration of creating a black flame without trick photography.

Explanation of how sodium streetlights with a low Color Rendering Index (CRI) can create a black flame effect.

Introduction of the concept of electron orbitals and how they relate to the color of light emitted by elements.

The unique yellow-orange light emitted by sodium due to a specific electron transition.

Use of a diffraction grating to split light into its constituent colors, demonstrating the broad spectrum of xenon gas.

The dual emission lines of sodium that are close together and not easily distinguishable.

How the black flame effect is achieved through the absorption of specific photons by ground-state sodium atoms.

The role of methanol in creating an almost invisible flame for the black flame experiment.

The absorption of 590-nanometer photons by ground-state sodium atoms, causing the flame to appear dark.

Clarification on why the flame's own light production does not negate the black flame effect.

The scattering of light and its effect on the visibility of the flame against a lit background.

Introduction of glassblower glasses that block specific wavelengths, aiding in working with bright, colored flames.

Testing of EnChroma glasses, which claim to enhance color vision for people with red-green colorblindness.

The use of neodymium and praseodymium in glassblower glasses to filter out the sodium emission line.

The difference in absorption and emission spectra of sodium in gas form versus when bound in glass.

EnChroma glasses creating a notch in the spectrum that corresponds with their claims of aiding colorblind individuals.

Discussion on the effectiveness and marketing practices of EnChroma glasses, and the subjective experience of users.

Historical context of Bunsen burners and their role in spectroscopy and the discovery of new elements.

Transcripts

00:00

- In this video,

00:00

I'm going to show you how to make a black flame.

00:03

There's no trick here.

00:04

Like I haven't inverted the colors or anything like that.

00:07

The explanation for how it works is really cool.

00:10

And along the way we'll learn one weird trick

00:12

that glassblowers use to make fire invisible.

00:15

So I did say

00:16

that there was no trick photography in this footage,

00:19

but actually the fact that it's black and white

00:21

is sort of a trick.

00:23

If I put it back to full color

00:24

and then turn off the auto white balance on my camera,

00:27

you'll see that everything's very yellow.

00:29

That's because I'm illuminating the scene

00:31

with one of these old-fashioned streetlights

00:34

called a sodium streetlight.

00:35

Sodium streetlights were used for a long time

00:37

because they're incredibly efficient.

00:38

Unfortunately, sodium streetlights

00:40

make everything look weird.

00:41

Like you know there's this number,

00:43

the CRI for a light bulb,

00:46

and it tells you, how good is this light source

00:49

at making colors look the way they are naturally?

00:53

Sunlight has a CRI of 100,

00:55

and a light source that doesn't allow you

00:57

to distinguish color at all would have a CRI of zero.

01:01

And, well, sodium streetlights have a CRI of zero.

01:06

But what makes them so bad at rendering color

01:08

is also the thing that turns this flame black.

01:12

You might know this already,

01:13

but if you excite an atom in the right way,

01:15

an electron will jump up to a higher orbital,

01:18

and when it drops back down again,

01:20

it releases a photon of light.

01:22

How much energy the photon has

01:23

is just the difference between the two energy levels.

01:26

The electron is giving up some of the energy it had up here

01:29

and it's throwing it away in the form of a photon.

01:32

But because these orbitals are quantized,

01:34

their energy levels are fixed,

01:36

which means the energy of a photon

01:38

released by that transition will always be the same.

01:41

And the energy of a photon defines its color.

01:44

And for sodium, there's only really one possible transition

01:47

that exists within the visible spectrum,

01:49

which gives off photons

01:50

with about a third of a femtojoule of energy,

01:53

and they have this yellow-orange color.

01:55

You don't normally talk about

01:56

the femtojoules of a photon, by the way.

01:59

You usually talk about the wavelength,

02:00

in this case 590 nanometers.

02:03

It's actually quite unusual for an element

02:05

to only have one strong visible line like this.

02:08

For example, I've got some xenon gas in this vial,

02:11

and when I excite it

02:12

with electricity via this tiny Tesla coil,

02:15

you get this lovely color.

02:16

To see what that color is made of,

02:17

I could use a prism in the same way that Newton used a prism

02:21

to find out that sunlight

02:22

was made up of the full spectrum of colors.

02:24

Instead of a prism, though,

02:25

I'll use a diffraction grating.

02:27

You see how it split sunlight into a rainbow

02:29

just like a prism

02:30

when I put it in front of the lens of my camera.

02:33

Putting the diffraction grating in front of the xenon

02:36

shows us that although it looks white,

02:38

it's actually made up of lots of discreet lines

02:41

instead of the full spectrum.

02:43

Compare that to sodium, which has just the one line.

02:45

I keep saying that sodium has just one line,

02:47

but that's not strictly true.

02:49

There are in fact two emission lines very close together.

02:52

We just can't distinguish it with this setup.

02:54

I'll get to that later though,

02:55

because I really wanna explain this black flame thing first.

02:58

So, an atom of sodium emits a very specific color of photon

03:02

when an electron drops from the 3p orbital

03:05

to the 3s orbital.

03:06

But the opposite also happens.

03:08

If you can hit a sodium atom

03:10

with a photon that has just the right energy,

03:13

the electron will jump

03:14

from the 3s orbital to the 3p orbital,

03:17

absorbing that photon.

03:19

If the photon has too little energy,

03:20

the sodium atom won't absorb it,

03:22

but also, if it's got too much energy,

03:23

the sodium atom won't absorb it either.

03:25

So as well as having an emission spectrum,

03:27

sodium also has an absorption spectrum,

03:30

which is just the inverse of the emission spectrum.

03:33

And with that simple fact we can explain the black flame.

03:36

So there are at least two ways to excite sodium atoms

03:39

so that they give off orange light.

03:40

The sodium streetlamp uses electricity,

03:43

which when you get down to it, is actually about collisions.

03:46

Electrons streaming from the anode to the cathode

03:48

smack into those sodium atoms,

03:50

and that's what causes the jump in energy levels.

03:53

The other way to do it is with heat.

03:55

So I start off with a methanol flame.

03:57

The reason I'm choosing methanol

03:59

is because it burns with an almost invisible fire.

04:02

I actually don't want any light from the fire itself,

04:04

because now I add a bit of salt water.

04:07

The heat from the fire vaporizes the sodium in the salt

04:10

and excites it at the same time.

04:12

It causes the valence electron to jump up.

04:13

And when it drops back down, it releases that orange photon,

04:17

which is why the flame is orange.

04:19

So all the time in that flame,

04:21

you've got a mixture of excited sodium

04:23

and sodium in the ground state,

04:25

and it's those ground-state sodium atoms

04:27

that make the trick work.

04:29

Because remember, those ground-state sodium atoms

04:31

are really good at absorbing 590-nanometer photons,

04:35

which is the exact photons

04:36

that are being produced by the sodium streetlight.

04:38

And of course, if the flame is absorbing photons,

04:41

it's going to look dark.

04:42

And that's normally the end of the explanation,

04:44

but I think it's important to clear up two things.

04:47

The first question you might have is like,

04:48

okay, the flame is absorbing photons from the lamp,

04:52

but it's also producing photons of its own.

04:54

In normal lighting conditions,

04:56

you can see that this flame is producing lots of light.

04:59

So don't these two things cancel out?

05:02

Well, the answer to that is that my sodium streetlight

05:05

is just a lot brighter than the flame,

05:07

so the tiny amount of light produced by the flame itself

05:10

is pretty negligible.

05:11

But the more important question that you might have is this;

05:14

after a sodium atom has absorbed

05:16

one of the orange photons from the streetlight,

05:19

it's just going to remit it again almost straight away.

05:22

So if one photon is emitted

05:24

for every photon that's absorbed,

05:26

it shouldn't look black at all.

05:28

But let's think about what you're actually seeing here.

05:31

To the left of the flame,

05:32

you can see the white wall behind it

05:34

is well illuminated with that orange light.

05:37

The fact that you can see the wall

05:38

means that those orange photons

05:40

are traveling from the wall into your eyes,

05:43

or in this case into the lens of my camera.

05:45

The bit of wall behind the flame

05:47

is also well illuminated by the sodium streetlight.

05:49

But when the photons leaving the wall

05:51

begin their journey into my camera lens,

05:53

they have to pass through the flame,

05:55

and when they do,

05:56

they get absorbed by the sodium atoms in the flame.

05:58

And yes, for every photon that's absorbed,

06:01

a new photon is emitted.

06:03

But crucially, the newly-emitted photon

06:05

will be traveling in a completely random direction.

06:08

The chance that it will be pointing

06:10

towards the camera lens is very low.

06:12

In other words, the light from the wall behind the flame

06:14

is scattered in all directions,

06:16

leaving a dark patch behind.

06:18

All this reminds me of something really cool

06:20

that my friend Andrea Sella showed me;

06:22

these special glasses worn by Glassblowers.

06:26

They do something amazing and I wanted to see it in action,

06:29

so I went to visit the glassblower

06:31

at University College London.

06:33

John here is working a piece of glass with a blowtorch,

06:36

and because the glass has a bit of sodium in it,

06:39

as the temperature goes up,

06:40

eventually some of that sodium starts to vaporize

06:43

and we see that characteristic orange light.

06:46

Eventually it gets so bright

06:47

that it's hard for John to see what he's doing.

06:49

But look what happens

06:50

when I put this special pair of glasses

06:52

in front of my camera lens.

06:54

Isn't that amazing?

06:55

It completely blocks that orange light

06:57

and suddenly John can see what he's working with.

07:00

While I was running tests

07:01

on the glassblower glasses for this video,

07:03

I realized that I now have the equipment that I need

07:06

to run tests on these EnChroma glasses

07:08

that I've had lying around for years.

07:10

I've wanted to run the tests for a long time

07:12

because when I heard about them, I was skeptical.

07:15

Like they claim to enhance color vision

07:17

for people with red-green colorblindness,

07:19

but how can something that removes light

07:22

help someone to see colors

07:24

that they don't have the anatomy for?

07:27

So we're gonna test whether the way these work

07:29

matches the way EnChroma says they work.

07:33

Wait, if EnChroma can sell these,

07:38

I bet I could sell these.

07:40

Are there still some old sodium streetlights where you live?

07:43

Do you hate the color?

07:45

Would you rather see nothing at all?

07:47

Then you should try EnMouldia glasses.

07:50

They'll completely cut out that horrible orange glow.

07:54

Don't use while driving at night.

07:55

Don't use while walking at night.

07:57

That's the advert sorted.

07:59

Ah, I'm gonna need a website.

08:00

I know, I'll use the sponsor of this video, Odoo.

08:04

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08:06

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08:07

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08:10

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08:12

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08:15

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08:16

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08:19

inventory, et cetera, et cetera.

08:21

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08:24

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08:25

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08:28

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08:30

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08:32

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08:34

for getting the website up and running.

08:35

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08:55

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08:57

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08:59

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09:01

Check out the link in the description

09:02

to try out Odoo for yourself.

09:04

Right, so to figure out

09:05

what these pairs of glasses are doing to the spectrum,

09:07

we need to make some improvements

09:09

to this setup that I showed you earlier

09:11

where I was putting a diffraction grating

09:13

in front of my camera.

09:14

And that's exactly what this is for.

09:16

There's some kind of webcam at the end of this tube

09:19

and at the other end you've got the slit,

09:21

and there's a diffraction grating in there somewhere too.

09:24

And you can point that slit

09:25

at anything you want to find the spectrum of.

09:27

And it really is just a webcam.

09:29

Look, I can switch

09:30

from my built-in laptop webcam to this one.

09:33

I might actually use this for Zoom meetings, you know.

09:35

But with some special software

09:36

I can focus in on just the spectrum part of the image,

09:39

and from that it spits out a graph.

09:41

When I point it at the sodium streetlight,

09:43

you can see there's the 590 nanometers.

09:46

This is much more precise than I was doing before,

09:48

but you still can't see two individual peaks.

09:51

This device has a resolution

09:52

of about plus or minus two nanometers of wavelength,

09:54

but the two sodium peaks are about 0.6 nanometers apart.

09:57

There's another little peak in the infrared,

09:59

which I believe is also coming from sodium,

10:03

but it's weirdly hard to fact-check that.

10:04

There are also little peaks either side of the main peak,

10:08

which I believe are also coming from sodium,

10:10

but people don't talk about them because,

10:13

well, they're so much weaker than the main peak.

10:15

The reason the webcam inside this device

10:17

can see infrared and a bit of ultraviolet

10:20

is because, well, all webcams can,

10:23

it's just most of them have a filter

10:25

to block those parts out,

10:26

but that filter was removed

10:28

from the webcam inside this device.

10:30

Look, this is Chris Wesley removing the filter

10:33

before putting it into one of his devices.

10:36

It's a great bit of kit, by the way.

10:37

Like you could spend maybe 1,000 pounds

10:40

on a similarly capable spectrometer,

10:43

but this one made from 3D printed parts

10:45

and a modified webcam and a cardboard tube

10:48

is less than 200 pounds.

10:51

If you're interested,

10:51

there's a link to Chris' website in the description.

10:54

I did have a go with this spectrometer at UCL,

10:56

and you can kind of see a doublet there.

10:58

The reason there are two lines instead of one, by the way,

11:01

is because of electron spin.

11:02

So you might know that electrons

11:03

have this property called spin.

11:05

It's not like spin in the classical sense

11:07

of something spinning around,

11:09

because an electron is a point-like particle.

11:11

How can something that's one-dimensional have spin?

11:14

Doesn't make sense.

11:15

But it is like spin in the classical sense

11:17

of it gives the electron angular momentum.

11:20

And by the way, that's my new favorite

11:23

profound and weird fact about the universe.

11:26

How can a point-like particle have angular momentum?

11:29

This angular momentum turns the electron into a magnet.

11:32

And because it's quantized,

11:34

that magnet is either pointing upwards or downwards.

11:37

That's the spin up and spin down

11:39

that you might have heard of.

11:41

And that causes them to have subtly different energy levels.

11:43

But that never made sense to me,

11:44

because, like, they're just the mirror image of each other.

11:47

How can one have more energy than the other?

11:50

And it turns out it's to do with the orbitals.

11:52

Like you know how a moon

11:53

can be going around a planet like that,

11:56

and the moon can be spinning either in the same direction,

11:59

so they're both spinning clockwise.

12:01

That's prograde spin.

12:02

Or it can be spinning

12:03

in the opposite direction to the orbit.

12:06

That's retrograde spin.

12:08

And the same goes for atoms.

12:10

An orbital can have angular momentum

12:12

in one direction or the other,

12:14

which creates another magnet.

12:16

And that magnet is either in the same direction

12:19

as the electron spin magnet

12:21

or it's in the opposite direction.

12:23

If it's in the opposite direction,

12:24

they're attracted to each other more strongly

12:27

and that changes the energy levels

12:29

and that's how you get the split.

12:30

Okay, so now let's shine sunlight into this thing.

12:33

That dip in the infrared, by the way,

12:34

is the signature of oxygen.

12:36

So we know that the oxygen in the atmosphere

12:38

must be absorbing some of that wavelength

12:41

from the sunlight that's hitting the Earth.

12:43

I wouldn't see that dip

12:44

if I was doing this experiment in the vacuum of space,

12:48

because I'd be dead.

12:49

And look, if I put the glassblower glasses in front,

12:52

there's that dip in just exactly the right spot

12:55

for the sodium line.

12:56

That notch is achieved by the addition

12:59

of neodymium and praseodymium to the glasses.

13:02

The absorption spectrum of those elements

13:04

nicely cut out the sodium line.

13:06

It's also cutting out some of the green there.

13:08

I think that's just some different transitions

13:11

of neodymium and praseodymium.

13:13

Here's something I don't understand, though.

13:14

Like in the black flame experiment,

13:16

we're seeing that sodium will absorb the sodium line.

13:19

So why do glassblowers use neodymium and praseodymium?

13:22

Why not just put a load of sodium in the glasses?

13:25

Shouldn't that be good at absorbing the orange light?

13:27

Well, it turns out that sodium only emits

13:30

590-nanometer light when it's in gas form.

13:33

When sodium is bound up in glass,

13:35

its emission and absorption spectrums are different,

13:38

which makes sense because those valence electrons

13:40

are going to be involved in the bonding somehow.

13:42

But neodymium and praseodymium are different.

13:45

They're lanthanides,

13:46

and it turns out that the orbitals

13:48

of the valence electrons in lanthanides

13:51

are actually relatively small

13:52

compared to the orbitals that are already full.

13:54

In other words, they're kind of hidden away

13:56

from what's going on around them.

13:58

So the absorption spectrum of neodymium and praseodymium

14:00

are unaffected by whether it's in a gas form

14:03

or whether it's bonded to something else

14:05

or whether it's part of a larger solid.

14:06

So finally we get to the question of EnChroma glasses.

14:10

What do these glasses do

14:12

to the spectrum of light entering them?

14:14

So if I point my spectrometer at sunlight

14:16

and then put the EnChroma glasses in front,

14:18

this is what we see.

14:19

So this is interesting.

14:20

You've got this notch here,

14:22

and actually that does correspond

14:24

with the claims of EnChroma.

14:26

The logic goes like this.

14:27

The most common type of colorblindness

14:29

comes from the sensitivity

14:30

of the red cones and the green cones overlapping too much.

14:33

So if most of the confusion happens

14:35

around the peak of those absorptions

14:37

where they're really overlapping,

14:39

you can cut out that peak with special glasses.

14:42

Then maybe your red and green cones

14:43

can distinguish between what's left on either side.

14:46

This particular pair are for outdoor use,

14:49

so they're also lowering everything,

14:51

like a pair of shades would.

14:52

So the glasses are doing what they claim to be doing

14:55

in terms of their mode of operation,

14:58

but whether they help colorblind people

15:00

to see colors that they couldn't before is another question.

15:03

I actually don't wanna comment on that too much,

15:05

and that's for two reasons.

15:07

The first is it's a weirdly polarized topic now

15:10

and I don't like being shouted at,

15:12

but the other reason is, like,

15:14

the published literature on the subject

15:16

doesn't seem particularly conclusive.

15:19

If I had to summarize the literature,

15:20

it would probably be that there is no evidence

15:23

that they help with colorblind tests.

15:26

Though it does seem like that's because certain tests

15:30

it helps you to be able to perceive,

15:33

but at the same time, there are other tests

15:35

that it stops you being able to perceive.

15:38

So overall, you don't have an improvement on those tests.

15:42

Part of the reason

15:43

for the polarization around EnChroma glasses

15:46

I think is because of their dubious marketing practices.

15:49

Like when these arrived,

15:50

there was a little note with them

15:52

suggesting that I should film the reaction

15:54

of the person they were intended for

15:57

and then post it to social media.

15:58

But then of course,

15:59

you're gonna have a publication bias, aren't you?

16:01

Like I filmed my nephew using these

16:05

and they didn't really have an effect,

16:08

so of course I didn't post the video anywhere.

16:10

That was about four years ago, by the way,

16:12

and that particular nephew

16:14

now has a YouTube channel of his own.

16:17

If you're even vaguely interested in "Gorilla Tag,"

16:19

I highly recommend it.

16:20

Link in the card in the description.

16:22

EnChroma don't claim that these glasses

16:24

work for all colorblind people.

16:26

And of course, it's not just about

16:28

passing colorblindness tests,

16:30

which the literature seems to be focused on.

16:33

It's about your experience.

16:35

Like, of course it's worth the money

16:37

if when you put them on they make you happier

16:40

by that amount of money.

16:42

So you could go to an optician,

16:44

some opticians sell these, you could try them,

16:46

and if they pass the happiness versus money test

16:48

and you don't care about their dubious marketing practices

16:51

and you don't care whether they make you happier

16:53

than a placebo pair of shades

16:55

under clinical testing conditions,

16:57

then maybe EnChroma glasses are for you.

17:01

But EnMouldia glasses,

17:04

well they're for everyone.

17:05

God, that's a good ending to the video, isn't it?

17:07

It's a shame that I'm gonna carry on going,

17:08

'cause there's one more thing that I wanna tell you.

17:10

It's this really cool fact about Bunsen burners.

17:13

What we've been doing in this video is spectroscopy,

17:15

and it's the method by which loads of new elements

17:18

were discovered back in the day.

17:19

Robert Bunsen was one of the scientists

17:21

using that technique,

17:22

and he would heat his elements with a flame.

17:25

So like me, he needed a flame

17:28

that produced hardly any light of its own,

17:30

because that obscures the result.

17:32

To do that, he needed a burner

17:34

that would mix oxygen into the gas supply before it was lit.

17:37

In other words, that twiddly thing

17:39

at the bottom of a Bunsen burner

17:40

was put there to help us find new elements.

17:44

(upbeat jazzy music)

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関連タグ
Black FlameSodium LampsColor AbsorptionSpectroscopyLight EmissionChemical ReactionsScientific ExperimentGlassblowing TechniqueEnChroma GlassesBunsen Burner
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