Today.

We're talking about why I can't tell my rubbish bins apart when I go out the night before to put them to the curb.

You may be like me.

You have multiple bins that are due to be put out on different dates.

You have to keep track of when the recycling goes out.

When the normal rubbish goes out and here, not in him.

We have several bins we have to put out.

In my case, one is green, one is black, one is brown, and often when you go out at night, you can't actually tell them apart.

And that's because much of the illumination that we get now from streetlights comes from a certain kind of lamp called sodium lamp.

That is changing, however, certainly here not am around the country and probably in place around the world.

There's a big drive towards replacing those sodium bulbs by led light light emitting diodes, which give a very different kind of light.

So today we're gonna talk about why, under sodium lamps.

We can't distinguish colors very well.

This is a light source that is emitting light at only a single particular wavelength, 589 nanometers.

And that corresponds to a very yellow orange light, as you can see, because that's the wavelength of yellow in the optical spectrum.

So there's a tube in here in which atoms of sodium are being excited.

The electrons are jumping up to high energy levels.

When they fall down, they emit a certain wavelength of light, corresponding to the energy difference between those energy levels.

Well, the question is, why do we see color, asshole?

If we're outside in the daytime and our only source of illumination is the sun, then the son we know emits light at all wavelengths and together that makes a very white ish light.

It doesn't emit light exactly the same amount at each wavelength, but overall it covers the whole spectrum.

However, when we have an artificial source of light, we're not always going to get that full spectrum wavelength coverage.

And here's a really extreme case of that, so we don't have white light at all.

We only have one specific wavelength.

This very very yellow light on.

So when we have white light, it may hit objects.

Some of that light will be absorbed, some will be transmitted and some will be reflected.

It's on Lee the light that's reflected back to us that gives an object of color.

So in the case of white light, all of those wavelengths are provided, and only some of them, you know, bounce back to us if you don't have that full spectrum to begin with, If you're only bouncing light of a certain color off your object, you're not going to be able to distinguish.

What is true color is so these air really fun.

These air diffraction glasses and so etched in very, very fine find much more finding you could actually see our little grooves etched into the plastic.

And what happens when the light passes through?

Those is its defected, so it spreads out like a prison will spread out white light, and it lets you see the whole rainbow of color.

So, Brady, if you put the glasses over your camera and you look at a white light source, you should see a pretty spectacular effect.

With that white light being spread out across all wavelengths in the spectrum.

So now you're seeing what is making up all that white light.

But if you then look at our sodium lamp, you're not gonna get that same effect.

Of course, there isn't that wide wavelength range to begin with.

To spread out, you should only see another image of the same lamp because that's all you have to defect.

So for comparison, here's the white light, and then you can have a look at the sodium lamp and see the difference.

Okay, so let's go into the white light here.

So here we have a fluorescent light emitting wavelengths from the blue to the red, which gives it a white appearance overall.

So we've got our our our pain as well in the vending machine, right?

So we've got the full rainbow here under the white light.

You know, the white light's bouncing off.

The blue light is bouncing off these ones.

We see them is blue.

The yellow light's bouncing off these ones.

Everything else is being absorbed.

However, we take them back to our sodium lamp.

We're going to see something very different flowing into the boat.

He's up now Yeah.

I mean, you can still tell which ones are light and which ones are dark.

But you've lost the Hugh.

You've lost the ability to distinguish what color it is.

Wavelength.

It is.

You can probably take a pretty good educated guess that that is yellow or orange, because it's matching the color of that life.

But beyond that, I think you'd be hard pressed to determine which one is blue.

Agreeing or purple.

So we've got some crayons here, but I don't think similarly you would be able Thio, tell apart which ones these are.

Do you wantto do to be calmer camerawoman?

Yeah, sure.

You have the camera.

I'll put you out of work.

This is your first time ever.

Yeah.

I'm Highlands.

I want you to take those crowns and write down what you think.

What color?

You think each one is using that crown?

I mean, I think they're all brown, but right, Brown for all of them.

I think that is bright.

I think they're all brown.

That might be orange.

That looks like a purple.

See, I think that looks yellow to red.

Maybe there's a great experiment.

Happy that my guess is All right.

So we got your colors down here.

Let's take it back into the white light.

Okay, so you got the yellow right, But then you did it again and thought it was orange on.

Then you got the green, right?

But I don't think you got anything else right?

Red was purple orange with purple.

Brown was red.

I'm pleased I got that one right.

Well, that's not surprising.

Causes yellow light eso Imagine a city where this is the only light source available at night when these air what the street lights look like in reality around here.

That's not quite the case because thes sodium lights, we have our high pressure sodium lights.

So while there intensely orange, they're not single wavelengths like this.

There's a bit of mercury in the tube.

It gives it a bit of coverage in the in the blue and the violet.

But there are cities around the world.

San Jose in California is one of them that uses or has used low pressure sodium lights completely to illuminate the city.

The reason San Jose did this is there's actually an astronomical observatory lick observatory on Mount Hamilton.

Not too far away.

So in the interests of helping the astronomers maintain the purity of the night sky, they legislated that they would use low pressure sodium lights on, and so they produce a light that's easily blocked out by filters.

For the astronomers, it makes everyday life for every night life very challenging because he can't distinguish colors.

You can't tell the colors of cars apart.

You pull up to a curb that's painted red for no parking.

You can't see it.

You get a ticket from the observatory's point of view if you've got a city that's nearby and growing and encroaching and having a lot of light pollution.

If you can keep that light at a single wavelength, then it's better than nothing, because you can have a filter in place that would remove on Lee that amount of light if the light is very broad spectrum very white.

Uh, there's no filter that you can use to remove all that, so just with one filter, you can make the city almost invisible to the telescope.

Well, things are changing now.

They're changing on a household level.

I've changed all my interior lights to led Sze because their energy efficient.

That costs a little more to put in.

But they're gonna last for 10 or 15 years, and they draw much, much less current.

So the running costs are much lower.

Ah, the same thing is happening on city and county would levels.

So street lights are being replaced with L.

E.

D's.

The advantages are, there's potentially better ability to distinguish color.

You get a more true representation of color.

They are more energy efficient, so they cost less to run.

They're more adaptable, so you condemn them and you can have the money on switches.

They don't take so long.

Toe light up on dhe.

If you get the casing right, you can direct them a little better as well.

But it's not.

It's not a cut and dry case.

Just because one bold is more energy efficient doesn't mean your overall savings.

We're gonna be greater if you go and put lots more light bulbs out there.

Some people don't like the glare.

There's a lot more reflection.

Some of that reflection may actually go up into the night sky, so it's not a tall clear that that's going to be better for light pollution.

This is a transformation that, as we make this video, is still very much in progress on it's gonna take some adaptation on everyone's part to get used to it.

What do you miss that yellow light from your childhood?

Like you have a form for you.

Glad I didn't go out at night anymore.

Actually, from me from the space station, you can actually see changes in cities as thes transformations take place.

You can see how city centres, you know, the very color of them changes as led lights or put in possibly really admitted as heat.

And so by the time they fall back to their ground state, they don't have as much energy to get rid of.

And so the energy they admit is lower energy than the energy they absorbed.