Incandescent bulbs in teaching

[Orodruin]

This thread got me thinking. Incandescent light bulbs were soft banned (as in, cannot be sold anymore) in the EU in 2016 and - if my google-fu is to be trusted - last year in the US. If you go to any store selling bulbs, all of them are LED, which makes sense both from many perspectives.* We are soon going to face a generation of students who have never in their life seen an incandescent bulb. Meanwhile, they are typically used as examples in many physics classrooms.

A couple of discussion points:
How should teachers deal with this in the coming years?
Do we need to start introductory classes by explaining what an incandescent bulb is?
What happens with the laboratory experience when physics student labs run out of bulbs (they tend to break) and cannot obtain more?
Should we simply phase out the incandescent bulbs from the curriculum?


* Anecdotally, we were visiting my in-laws in Spain recently with temperatures soaring towards 40 °C. Their second home is sparingly used and therefore was still all incandescent bulbs. It felt slightly absurd to be in Spain in summer, inside with the window blinders shut in almost complete darkness as turning the lights on would heat the house too much. Took a day or two to change all the lights in the house for LEDs.

 

[vela]

Apparently, there are still some specialty bulbs that haven't been banned in the US.

https://www.cnn.com/2023/08/01/business/incandescent-light-bulb-ban/index.html

 

[Orodruin]

Apparently, there are still some specialty bulbs that haven't been banned in the US.

https://www.cnn.com/2023/08/01/business/incandescent-light-bulb-ban/index.html

That doesn’t really address the questions in point though, ie, that students will generally be unfamiliar with the incandescent bulb.

 

[DaveE]

That doesn’t really address the questions in point though, ie, that students will generally be unfamiliar with the incandescent bulb.

Just like they were 10, 20, or 30 years ago. If you want to teach about incandescent bulbs, you will still be able to buy specialty bulbs for quite a while. Lots of equipment (microscopes, etc.) still need them. Afterall, I can still find nixie tubes on eBay. They just want to make it harder for homeowners shopping at the hardware store. OTOH, if you expect students to come to class with any knowledge of how the light in their bedroom is made, you may be disappointed, regardless of the technology. They'll tell you it's from switching a switch on the wall by the door.

 

[Orodruin]

30 years ago

That was probably around the time I started learning and I think myself and my classmates had at least some basic understanding about the filament glowing hot because of the energy dissipated in it.

Even if it still works as a demonstation tool, the connection to how light is produced in homes is lost. I feel that to at least some extent that will diminish the pedagogy. You can’t say ”this is how we make light at home”. That process of course will involve diodes which is not really your typical introduction to circuits.

 

[DaveE]

That was probably around the time I started learning and I think myself and my classmates had at least some basic understanding about the filament glowing hot because of the energy dissipated in it.

Even if it still works as a demonstation tool, the connection to how light is produced in homes is lost. I feel that to at least some extent that will diminish the pedagogy. You can’t say ”this is how we make light at home”. That process of course will involve diodes which is not really your typical introduction to circuits.

That is the nature of technology advances. Yes, I had to learn about vacuum diodes and triodes as an undergrad, but I always thought of them as if they were a strange version of MOSFET. All of these devices are complex enough that study is required regardless. I found the I-V characteristics of incandescents a bit confusing even later in my career; a complex non-linear thermo-electric device.

My big complaint is that all of the very basic circuit questions that use "light blubs" as if they are resistors. I guess they think it's easier because students had light blubs at home? But in reality, those are very complex circuits. Invariably the "correct" answers are actually wrong.

 

[kuruman]

How should teachers deal with this in the coming years?

I think that the "this" that teachers have to deal in the coming years goes beyond light bulbs and how they work. Clockwise and counterclockwise are becoming meaningless as are traditional clocks.

Also anecdotally, I was recently in a waiting room when a twenty-something asked me if I know what time it is. I was not wearing my watch so I point to the large (analog) clock on the wall above the receptionist's desk saying "There is a clock over there." He looks at me exasperated, moves his knapsack from the seat next to him to the floor, unzips a pocket, pulls out his cellphone, looks at it and nods his head without another look in my direction. I was impressed.

 

[Orodruin]

Clockwise and counterclockwise

I did not consider this for the simple reason that we do not say that in Swedish. We say essentially with-Sun and counter-Sun. The Sun is difficult to ignore unless young people stop going outside oh wait!

 

[berkeman]

Clockwise and counterclockwise are becoming meaningless as are traditional clocks.

Also anecdotally, I was recently in a waiting room when a twenty-something asked me if I know what time it is. I was not wearing my watch so I point to the large (analog) clock on the wall above the receptionist's desk saying "There is a clock over there." He looks at me exasperated, moves his knapsack from the seat next to him to the floor, unzips a pocket, pulls out his cellphone, looks at it and nods his head without another look in my direction. I was impressed.

I was shooting basketball hoops at a local park recently when a teen came up to me and asked me what time it was. I said that I leave my watch on the sidelines with my towel when I'm shooting, but he was welcome to go over and check the time. He replied that he did not know how to read an analog watch (which surprised me!), and I said "Don't worry, it's a digital watch."

He walked over and looked at my watch, and asked "What time is 1315?" (I forgot that I use military time on all of my clocks and watches...)

 

[kuruman]

He walked over and looked at my watch, and asked "What time is 1315?" (I forgot that I use military time on all of my clocks and watches...)

I can imagine the continuation of this.
You (seizing the teaching moment): Just subtract 1200 from 1315.
He: Can I borrow your calculator?

 

[gmax137]

Should we simply phase out the incandescent bulbs from the curriculum?

This is an interesting issue. When many of us here were in school, lightbulbs were ubiquitous and I remember many "electricity" lessons using "lantern" batteries, bell wire, knife switches, and flashlight bulbs.

Apparently the lantern batteries are still available, but at close to twenty bucks!

I do remember a bunch of these home experiment setups started with "get an ordinary buzz coil, and bla bla bla..." Well those things* were common garage detritus in the 1950s but now? I bet even the high school science teachers don't know what they are. I'm sure nobody designs lessons around them.

* https://en.wikipedia.org/wiki/Trembler_coil

 

[MidgetDwarf]

Stock up!!!

 

[jtbell]

I do remember a bunch of these home experiment setups started with "get an ordinary buzz coil, and bla bla bla..." Well those things* were common garage detritus in the 1950s but now?

I was a kid in the 1960s. I don't remember ever hearing about them! I had to do a Google search, and came up with your link.

 

[Orodruin]

Stock up!!!

This is actually a bad idea unless you have a particular reason. While a single LED bulb may be more expensive than a corresponding incandescent one, they have a much longer lifetime and cost less to use. An incandescent bulb is essentially a very inefficient heater with light as a side effect in terms of where the power goes. I do not remember the last time I changed a LED bulb because it broke.

 

[Nik_2213]

Before those chunky 6-Volt lantern batteries, remember the 'grid bias' variety with a row of sockets ??

Been a life-time, but I'd build simple logic and oscillator circuits using long-legged OC71 germaniums for the 'logic', and their modestly brawnier kin, OC72, to drive small relays --With snubbing diodes !!-- and/or 'bicycle bulb' micro-lamps and/or heat-sink warded 2N3055 (?) .
S-Decs rule, okay ??
Two invertor stages for a flip-flop, three flip-flap-flop, four twin flip-flops, but five, as four plus runt-pulse...
By 'ringing the changes' between related bi-, mono- and astable varieties and timings, not forgetting their Schmitt cousin and OC72 mini-power stages etc, good fun was had.
Sadly, though I wanted to do electronics / electronic engineering, my calculus was not good enough...

 

[Vanadium 50]

A few comments on LEDs.

• My house has virtually no incansescents. Hasn't since 1997. "Virtually" means I think one outdoor light might still be old school.
• "LED last a long time" is a myth. Sometimes they do, sometimes they don't. The failure mode seems to be the base. El-cheapo bulbs from China seem to be worst in that respect.
• "People smarter than you have decided for you that this is not a good choice and therefore you can be jailed for it" has generated a lot of backlash, and has raised the profile of some rather unsavory characters. By the time incandescents were banned in the US, they were already well on the way out, so this really was unnecessary from a policy perspective.

Now, you can still buy incandescants in the US. The loophole is "specialty bulbs". This includes things like heat bulbs, darkroom safelight (also on their way out, for different reasons) and the biggest one "decorative" bulbs - which includes bulbs where the filament is visible. So you should have little trouble in finding them: all the big online retailers have them. It's been a year or two since I've been to a "Mn. Bricolage" in France, but they had a few even then.

That said, I am not sure of the pedagogy. I doubt very much that the student is familiar with how a light bulb works coming in. As a a visual example of a resistor, they are not very good resistors.

 

[berkeman]

Just remember, without incandescent light bulbs, there likely would have been no Hewlett Packard, and no Disney Fantasia.

https://www.hewlettpackardhistory.com/item/a-deal-with-disney/

 

[kuruman]

Just remember, without incandescent light bulbs, there likely would have been no Hewlett Packard, and no Disney Fantasia.

https://www.hewlettpackardhistory.com/item/a-deal-with-disney/

And no "How many (human subgroup) does it take to screw on a lightbulb?" jokes either.

 

[DaveE]

"LED last a long time" is a myth. Sometimes they do, sometimes they don't. The failure mode seems to be the base. El-cheapo bulbs from China seem to be worst in that respect.

Yep. The stuff in a typical incandescent bulb can get really hot and still work for a long time. They're also resistant to thermal cycles (even though that's the big culprit in their reliability). This isn't true of semiconductors, including the control circuits. So LED bulbs are more efficient, but they are much worse at dealing with thermal stress. The big heat sinks often required are an issue. Of course this can all be solved, but there's a lot of opportunity to create a cheap design in both senses of that word.

My complaint is that I don't really know how to choose the good ones. I've had relatively early failures from some big name brands. These were in backwards compatible Edison screw base bulbs, which somewhat ties the hands of the manufacturers; some older fixtures will cook the LEDs.

 

[kuruman]

Seriously, though, going back to the title of this thread I have found that lightbulbs in circuits are useful in qualitative questions of the conceptual variety. Their glow is a measure of the power they dissipate, something that cannot be deduced by looking at regular resistors.

For example, I give the circuit on the right and ask,

• Rank the three bulbs from brightest to dimmest. Explain.
• If bulb H is unscrewed, which of the remaining bulbs is brighter than the other? Explain.
• If bulb H is unscrewed, does bulb F glow dimmer, brighter or the same as before? Explain.
• If bulb H is unscrewed, does bulb G glow dimmer, brighter or the same as before? Explain.

 

[Vanadium 50]

My complaint is that I don't really know how to choose the good ones. I've had relatively early failures from some big name brands.

Me too, but it has been better for the big name brand than "Yang's Bait, Tackle and Bulbs". The failure mode seems to be base gets hot, electronics don't like it and get even hotter, and then the bulb stops working.

The solution is to standardize on a connector so you have the electronics screw into a regular Edison screw and the bulb proper screws into that. I suspect this will not be economical.

Their glow is a measure of the power they dissipate, something that cannot be deduced by looking at regular resistors.

So, what is the purpose of this? Why do students need to know something specific to a kind of light bulb taht no longer is in regular use?

 

[DaveE]

View attachment 349735Seriously, though, going back to the title of this thread I have found that lightbulbs in circuits are useful in qualitative questions of the conceptual variety. Their glow is a measure of the power they dissipate, something that cannot be deduced by looking at regular resistors.

For example, I give the circuit on the right and ask,

• Rank the three bulbs from brightest to dimmest. Explain.
• If bulb H is unscrewed, which of the remaining bulbs is brighter than the other? Explain.
• If bulb H is unscrewed, does bulb F glow dimmer, brighter or the same as before? Explain.
• If bulb H is unscrewed, does bulb G glow dimmer, brighter or the same as before? Explain.

Like an electronics for poets class, I guess?
I'd skip right to KCL & KVL with simple networks and have them calculate those things. Then they could measure it with a $10 DMM. Because that's what they'll really do later if they ever need to know about this stuff.

 

[kuruman]

Like an electronics for poets class, I guess?

More like introductory physics for engineers. I was amazed at how students who had already seen KVL in high school got tripped up by this. There were always a few who said that removing bulb H meant replacing it with a "straight wire" thereby shorting bulb G.

 

[DaveE]

The solution is to standardize on a connector so you have the electronics screw into a regular Edison screw and the bulb proper screws into that. I suspect this will not be economical.

I think one issue is that they want to use the socket as part of the heat dissipation path. They've inherited a difficult thermal problem; work in any sort of Edison fixture. Of course that all depends on the design details.

 

[DaveE]

I was amazed at how students who had already seen KVL in high school got tripped up by this.

Then they didn't really know Kirchhoff and need a refresher, IMO. Sorry, I think engineers need to be able to learn intro physics and EE in the way they'll have to actually know and use it. I just don't see how light bulbs are better than resistors for this sort of lesson. Again, you can buy a DMM for $10. Bonus: they get to learn a tiny bit about using measuring instruments and processing the data they give.

 

[kuruman]

Then they didn't really know Kirchhoff and need a refresher, IMO.

Exactly my point for asking questions like this. To bring forth faulty understanding.

Sorry, I think engineers need to be able to learn intro physics and EE in the way they'll have to actually know and use it.

Here we disagree. I believe that engineers need to learn intro physics from physicists and calculus from mathematicians. They can then take engineering courses to see how "all that theoretical stuff" can be brought together and applied to engineering tasks.

An engineering student asked me once, "why do you spend so much lecture time doing all these derivations? Just give us the equations to plug in." I said, "when the time comes for you to design something innovative, there will be no equations to plug in. You will have to know how to derive them yourself and you need to see how to put together the reasoning that goes into them."

 

[DaveE]

Sorry, I think engineers need to be able to learn intro physics and EE in the way they'll have to actually know and use it.

An engineering student asked me once, "why do you spend so much lecture time doing all these derivations? Just give us the equations to plug in."

I don't think we do disagree, that sounds like the right way. The way I learned and practiced EE, understanding was required. I maybe out of touch with many engineering programs, but "just give an equation" wasn't ever the way it was done at my schools. When I was hiring analog EEs, you wouldn't ever get past my interview if you didn't understand what you were actually doing; and, honestly, most didn't, even for pretty basic questions.

 

[Orodruin]

bulbs where the filament is visible

There are LED bulbs with ”filaments” too for this very purpose.

El-cheapo bulbs from China seem to be worst in that respect.

You get what you pay for - as always. I still don’t remember the last time I changed a LED bulb*. I do remember the feeling of annoyance when an incandescent bulb gives in when you flip the switch and having to keep a supply of bulbs at home just in case.

* I do remember the last time I saw a LED bulb break … it was not the bulb’s fault.

Why do students need to know something specific to a kind of light bulb taht no longer is in regular use?

It is not about learning about the bulb, it is about the visual representation of power dissipation.

 

[pinball1970]

We have them in our light boxes but the the newest of those is seven years old.

 

[Vanadium 50]

can buy a DMM for $10.

$4.59 at Harbor Freight. ("Tools to last a lunchtime.")

Mine is a Fluke 77. I got a deal, but it did not costv$4.59.