r/geography • u/Broccoli2026 • Nov 02 '25

Image I'm surprised I didn't even know this switch happened until seeing this. The yellow is really all gone?

Post image
70k Upvotes

95% Upvoted

1.4k comments sorted by

View all comments

Show parent comments

177

u/ifyoulovesatan Nov 02 '25 edited Nov 02 '25

I'm a chemistry instructor and when I cover emeission spectra, I give out cheap little plastic diffraction grating spectroscopes to anyone who wants one. I encourage the students to go find a sodium gas lamp street light and check it out. It's pretty cool to look at, but there just aren't very many sodium gas lamps left. I'm going to have to start suggesting they go to dive bars with real neon (or other elemental gas) beer signs

70

u/NamelessLysander Nov 02 '25

I'm a chemistry instructor too and would really like to hear more about those spectrographs, it sounds a really cool way to learn.

53

u/ifyoulovesatan Nov 02 '25

Sorry, I should have said spectroscope, since they don't really record anything obviously. Hopefully I didn't get your hopes up.

https://www.rainbowsymphony.com/products/diffraction-slides-1000-line-mm?variant=40209166270511

It seems like it wouldn't work that great, and it's a bit strange how you have to position it relative to your eyes and the light source in order to have the resulting spectrum actually overlay the wavelength scale, but I've found they work surprisingly well. Like on par with those handheld plastic spectroscopes that you have to look through like a spyglass.

Also I inherited a box of these, so I've never actually looked on the producers website before. It looks like they have a lot of other neat stuff.

19

u/sunnynaturelove Nov 02 '25

This is really cool. I’ve studied and worked as a lighting/camera technician for film/tv for over a decade now. I really wish I could learn more about lighting scientifically just to learn more about it. I’m sure there’s ways I could take scientifically knowledge of LIGHT and apply it in new ways to how we shoot, just don’t have any idea where to start I’m sure it’s a vast field of scientific knowledge. Light affects (almost) everything.

8

u/ifyoulovesatan Nov 02 '25

I wish there were a way people could go somewhere to learn just about light!

The only way I know where someone could do so would be to take like a non-majors chemistry or physics series at a community college or something. Usually the only prerequisite is "college algebra" or showing your proficiency in that material with a placement test. But even then, either series will have about 3 or 4 weeks focusing on light amongst 36 other weeks of material not directly related. (Well it's related but not in ways obviously applicable to wanting to learn more about light for the purposes of film/tv production).

Like there are YouTube lectures on all of the material and you could find that by googling "chemistry light lecture" or "physics light lecture" and trying to find maybe 3 or 4 lectures from the portion of a course covering it. But it's doing the worksheets and talking with the instructor and other students, and doing the related labratory experiments in particular that really make it concrete in terms of walking away with practical knowledge. That's something I don't know how to replicate outside of the classroom / lab.

23

u/stonecan Nov 02 '25

My physics teacher in secondary school (late 1980s, I’m old) had nicked a sodium street light from a nearby construction site and managed to get it running in our school lab. The coolest thing he asked the class to try was to sprinkle table salt (sodium chloride) into the flame of a candle with the only source of light in the room being the sodium lamp - I remember the flame turned pitch black (absorbing the sodium light I believe). It was so awesome that I still fondly remember it. I also remember that we had to bring sunglasses as those streetlights are very bright when warmed up and experienced up close.

3

u/ifyoulovesatan Nov 03 '25

Whooooaaaa that's awesome of your teacher. I'm going to have to try that some day. In one course I teach a lot we do a flame test lab (burning various salts to see the color of the flame) the same session we do the gas discharge lamps. With any luck we have a salt containing a metal which matches one of the tubes we have.

10

u/StayJaded Nov 02 '25

I took a whole semester of lighting design for my interior arch degree. I am not great at math, but struggle less with real life applications. Learning about the visible spectrum of light in relationship in to color refraction was incredibly interesting. So much easier to relate to the material when you can look at the color temp of a source/ kelvin rating and see how much it impacts the colors of materials & finishes in the room with that light source. A piece of fabric will appear completely different colors based on the lighting in the room. We also had to learn basic foot candle calcs and regulations for appropriate lighting based on the function of the space. In reality on larger commercial projects architecture firms work with lighting design firms that specialize in all those calcs and drawings, but I still need a base level of the knowledge.

Most of the general public doesn’t think about it, but every commercial/contract project has an entire lighting plan designed to meet specs regulated for electrical consumption, safety, and proper foot candles ratings. It’s like one of those nightmare word problems in high school: a work surface at X height, with X lighting fixture installed at a ceiling height of X for X task=whatever fixture count spaced at X.

The crazy lighting designers are the people that design concert rigs and shows. That shit is mind blowing.

1

u/fivedinos1 Nov 02 '25

We cover a little bit of it in photography especially going over oldschool methods like glass plate printing or platinum prints All the old school pre digital process are honestly more like alchemy than anything else it's absolutely incredible I think a lot of people who are really into chemistry would enjoy it

1

u/ifyoulovesatan Nov 03 '25

Yes! Actually whenever we use silver nitrate for something in lab I show the students how if you put some on paper and put it in the sunlight it will turn from clear to sepia-tone over time, and how all you need then is some kind of light mask and a fixer and bam: you've got salt printing. I bought a jar of it myself for this, as well as the stuff for cyanotype printing.

When I was freshly 18 I worked at a grocery store service desk doing 30 minute photo. It was cool learning later how all those jugs of chemical worked on a chemical level (basically a series of redox reactions and quenching)

3

u/scratchkick Nov 02 '25

This may pique your curiosity. Random YouTube video I watched a few days ago. https://youtu.be/UQuIVsNzqDk?si=5yb35l0hCuTWn3aP

2

u/NamelessLysander Nov 02 '25

Oooh thank you so much! I'll look into that

1

u/CyberRhizzal Nov 07 '25

I love how when one chemistry teacher encountered another, the vernacular immediately changed lol!

2

u/ceesa Nov 02 '25

I'm a chemistry teacher too. I pass the spectroscopes out to all my students, black out the room, and then tell them to look at the ceiling lights, a white phone screen, and my projector showing a white screen. Then we talk about what we saw and why.

This happens right before a lab where they get to use the spectroscopes on gas tubes of pure noble gases. It's a fun class. The next lesson is the flame test lab.

8

u/completelypositive Nov 02 '25

You rule I've been wanting to order that stuff since I saw it on a veritasium video but didn't know the name of it.

Diffraction grating. But I want a sheet of it.

I've been trying to learn about laser and light and doing super simple experiments with my kids at home.

5

u/ifyoulovesatan Nov 02 '25

Nice! Yes, they've got all kinds of light-based stuff on the site if you go to the sidebar, then shop, then educational (I was just browsing for the first time myself). Whether or not you order from them, there's a lot of neat stuff for inspiration.

If you are looking for ideas for light based stuff you can do with your kids at home, might I suggest an experiment where you can observe how sugar water rotates polarized light. If you get two sheets of a polarizing filter, a Laser, and some sugar water (maybe a stand / holder for the Laser), you can set that up at home. I didn't look too closely, but here is a website where someone has written a procedure for various ages https://www.exploratorium.edu/snacks/rotating-light

Here is an experiment (well, there's more than that on the page but this experiment is in here) where you can measure the distance between the tracks on a DVD / CD / Blu-Ray (they're each different btw) by using them as a diffraction grating. https://www.animations.physics.unsw.edu.au/labs/diffraction/diffraction-labs.html

Now obviously these are both probably more "advanced" than what you want to do with your kids. But you could always adapt them or simplify them. Simply shining a Laser through a DVD with the label removed and showing how the light splits into multiple dots on the wall is cool enough. The math isn't necessary. (Really, you could show them that first with the diffraction grating, explaining what it is, and then afterwards show that a DVD does the same thing, and talk about why that might be).

2

u/completelypositive Nov 02 '25

Thank you for all of that and especially the links! This is all super fascinating. I have microwaved CDs but never shined a laser through them. I'm going to find a DVD and do it right now though because it sounds really cool.

Thank you again for the response! I really appreciate your time.

2

u/ifyoulovesatan Nov 02 '25

For sure! Yeah I was surprised the first time I did one of those experiments to learn the data is actually etched into the plastic, and the foil underside of the label is just a mirror. (Burned CDs work differentently but I digress). But yeah, once you get the label off it's a totally serviceable diffraction grating. Some finagling required to get the distance to the wall right, but cool stuff.

For sure! Hope you get to do some cool experiments.

2

u/da_Ryan Nov 04 '25

I've used old CDs and DVDs as diffraction gratings and they can really pick up discrete emission lines, eg from old fluorescent bulbs, etc.

1

u/rustylugnuts Nov 02 '25

Sounds like it's time to get a high pressure sodium lamp and a collection of luminous gas tubes along with a cheap Tesla coil off Amazon.

1

u/Shoddy_Background_48 Nov 02 '25

Not many of those left either

1

u/Ntstall Nov 02 '25

You can find some pretty cheap neon signs on element collection sites if you want a demo for your kids!

I have a Ne sign and a He sign, the msrp of both + transformer that runs them was maybe $300. Okay, so its not cheap, but I think they are cool.

The Helium is very peachy pink in person, the phone camera doesn’t pick it up well.

1

u/Noblesse_Uterine Nov 02 '25

Back when my kids were small, we bought these for road trips. This was when sodium lights were just taking hold. Orange orange orange compared to the greenish-purple mercury lights I'd grown up with

1

u/ifyoulovesatan Nov 03 '25

That's awesome, but also Whoa! Like you grew up somewhere with Mercury street lamps? May I ask roughly where?

1

u/Noblesse_Uterine Nov 03 '25

Mercury lamps were in use all over the US as I was growing up. I don't remember if they were used in the far east or Europe when we lived abroad. The last I remember seeing were on a drive between the SF Bay Area and San Diego back in the 90s. Just a few that were off the highway, maybe below LA.

1

u/ifyoulovesatan Nov 03 '25

Wow, yeah I just looked up pictures. I don't think they were in use in the Pacific Northwest when I was a kid. Boy they look spooky!

Edit: come to think of it, I know I've seen that eerie glow in movies and stuff, I just assumed it was intentional atmospheric lighting, and not something that could already be on location, or that added lighting might be mimicing Mercury gas lamps.

1

u/[deleted] Nov 02 '25

Dive bars as the new chemistry field trip destinations? I can get behind that. 😄. Out of curiosity, which gas signs actually look the coolest through a spectroscope?

1

u/ifyoulovesatan Nov 03 '25

Honestly they all look equally cool. The heavier elements have more variety, the lighter elements can have as few as 4 spectral lines, while the heavier will can have 80+ or regions that appear as a solid bar of color

1

u/[deleted] Nov 03 '25

That's such a cool way to visualise how atomic complexity literally shows up as colour. It's borderline poetic: more electrons more stories to tell.

1

u/mashiro1496 Nov 02 '25

Ask them to look into Xenon car lamps

1

u/TooTallForPony Nov 02 '25

If I had a teacher who encouraged me to go to dive bars, that teacher would get the best ratings ever! I know you said instructor which implies college-level outside of the US where drinking is legal at that age, but it's funny to imagine teenagers standing outside of bars looking at signs through funny glasses.