Will incandescent light sources disappear?

[Stefano]

I have been thinking about this for a while. Since high (mains) voltage incandescent and halogen lightbulbs have been banned in most countries (and will be in all of them in the near future), and more and more people are switching (and must switch) to LEDs and energy-efficient lightbulbs, will tungsten-based light sources disappear completely in the near future?

 

If I understood correctly, low voltage (12 V) halogen lights are still legal in the EU. Also, some special lightbulbs, such as those made for ovens, must be incandescent, since you can not put an LED or a CFL bulb inside them (just the idea of a CFL in an oven is nasty for me). Car headlights and stop/position lights are still commonly halogen and incandescent respectively, but more and more people are switching to LEDs and HIDs, even though tungsten ones are still perfectly legal.

 

Will the demand for halogen lightbulbs drop so low that no company will be interested in manufacturing them? Will they disappear completely?

 

Yes, they are inefficient and they don’t last long. Everyone knows it. But they produce 100 CRI light, that is similar (to some extent) to natural sunlight. They are actual blackbodies, and pretty hot ones (tungsten can be pushed to more than 3400 ºC). They produce almost the same exact light a red giant produces (same temperature). Just add Fraunhofer lines, some broader absorption by something else, and you are done. They produce a continuous spectrum, from UV to IR, and no LED can do that at the moment. Low-voltage halogens have a compact filament and can be pushed to higher temperatures (I have 12 V ones that I run at 16-18 V. They will probably last only tens of hours if used this way, but it’s worth it). That’s why I like them.

 

I have 6 12 V 50 W downlights (4 with a vertical filament, 2 with a horizontal filament), 2 12 V 50 W capsules, a bunch of car headlights, a bunch of stoplights, some 6 V ones, 2 tiny 12 V 1.2 W capsules, a 230 V 25 W incandescent oven bulb, and some other stuff. I don’t lack tungsten sources. Their spectral bandwidth is still unmatched and, most of all, they are real blackbodies (as mentioned before). What do you think about this?

[Stefano]

I forgot a “?” in the title, I posted too early... I also forgot tags...

[Stefano]

Well, which tag should I put here?

[dabateman]

Easy bake ovens will definitely be bad in the future.

 

I have just started to see LEDs capable of being used in appliances. Our fridge has an led panel in side. Frezzer will get them and ovens will in time as well.

 

Might be the end, or the beginning of a new light.

[enricosavazzi]

Halogen bulbs are not really equivalent to incandescent bulbs, with respect to emission spectrum. The main difference is that halogen bulbs emit proportionally more VIS and less NIR, so they are a poorer choice as NIR sources than incandescent bulbs. The latter remain the cheapest and most convenient broadband NIR illumination sources for imaging.

 

Years ago I stocked up a dozen or so 60w incandescent floodlight bulbs, just in case incandescent bulbs disappear from stores. They haven't disappeared completely so far, but Sweden has an official policy of gradually phasing them out, starting with the higher powers (100 W are already gone I believe).

 

In the past 3-4 years or so, I replaced all illumination bulbs at home from incandescent to LED. One thing I can report is that the hype about durability of LED bulbs is just that - hype. I had at least a dozen LED bulbs burn out or develop other faults in the mean time, which is probably more than I would get with incandescent bulbs. Even though the LEDs themselves may be durable, their power supply electronics are built in China as cheaply as possible by companies that obviously cut as many corners as they can get away with.

[OlDoinyo]

Specialized bulbs such as heat lamps (for buffet tables and bathrooms) will continue to exist--they cannot be replaced with LEDs at present. Certain lamps made for reptile enclosures may also remain incandescent.

[Stefano]

I like tungsten sources for imaging, not for general purpose illumination. We too have all LEDs in our home. How will spectrometers work without halogen bulbs? Deuterium is good in deep UV, and xenon is peaky in the NIR. LEDs are good in VIS (what you really need is a smooth spectrum, not necessairly a continuous, flat one) but I don't know of any continuous NIR LED sources that can match a tungsten lamp (Thorlabs has a broadband LED which is quite good, but it lacks longer wavelengths). How about SWIR? SWIR LEDs are there, but they are very inefficient and weak (they have similar performances to those of UVC LEDs), and halogen sources emit tons of SWIR. Will someone keep producing them for special uses?

 

Edit: posted before reading OlDoinyo's post.

[Andrea B.]

Editor: how about using the "UV Lighting" tag? The tags are intended for broad application and are not too specific. Perhaps I should (whenever I get the time!!) change the name of the "UV Lighting" tag to "Lighting" or "Illumination".

[Stefano]

Done.

[Andy Perrin]

I certainly hope halogens remain for SWIR! My feeling is that incandescent lights will go the way of vacuum tubes (which were in fact direct descendants of incandescent lights via the Edison Effect). You can still get vacuum tubes for specialized uses but they have vanished from most equipment. The most common vacuum tube now is probably the magnetron in your microwave oven.

[Stefano]

You can find tungsten wire on ebay if you want to try some experiment. You have to remove oxygen, and that can be a bit tricky, and tungsten is also quite brittle, it can break. But surely a very fun metal to play with, you can heat it up almost as much as you want.

 

[Stefano]

Just tried an old 100 W 230 V incandescent lightbulb my dad found between stuff. It lights up a room quite well, and the light it produces is so delicate...

[Stefano]

How can you build a blackbody source hotter than ~3500 ºC (sublimation point of carbon)?

[Andy Perrin]

Why do you want one?

[Stefano]

It would be interesting to have it from a Physics point of view, it would simulate stars (such as our sun or even hotter stars) and it would have a broad visible and UV output. I never saw a blue-hot object except for some stars in the night sky or very specific phenomena like lightnings, although a blue-hot object would be so intense (small and bright) that it would be an eye-hazard to look at.

[Andy Perrin]

(Never mind, post erased)

[Stefano]

With tungsten or carbon you can’t even reach “real” white hot, you are still in the “yellow-hot” region. The sun is actually a bit bluer than how it appears, since the sky takes a bit of the blue away.

 

Yes, there is white-hot in between, there is this extra step.

[Andy Perrin]

I guess build a fusion reactor.

[Stefano]

Plasma could actually be an idea...?

[Bill De Jager]

How can you build a blackbody source hotter than ~3500 ºC (sublimation point of carbon)?

 

Use an arc welder to heat up tungsten to well beyond its melting point of 3400 C. The upper limit would be tungsten's boiling point of 5550 C, except you need a container to hold the melted tungsten. A hafnium carbide ceramic bowl won't melt until 3958 C. It might be expensive and hard to find, though. ;-)

 

I think the protective gear required would make it very cumbersome to do any photographic work, though. And the hard UV from the arc welder could really damage any plastics nearby.

[dabateman]

Use an arc welder to heat up tungsten to well beyond its melting point of 3400 C. The upper limit would be tungsten's boiling point of 5550 C, except you need a container to hold the melted tungsten. A hafnium carbide ceramic bowl won't melt until 3958 C. It might be expensive and hard to find, though. ;-)

 

I think the protective gear required would make it very cumbersome to do any photographic work, though. And the hard UV from the arc welder could really damage any plastics nearby.

 

These all sound like wonderful suggestions.

Please nobody try this.

 

[Editor's Note: Your eye-rolling editor bolded that request.]

[Stefano]

A 5500°C blackbody (if it is really black, so emissivity 1) irradiates a tremendous amount of light. It would require a lot of power to keep a very small object at that temperature.

[Bill De Jager]

These all sound like wonderful suggestions.

Please nobody try this.

 

Of course I was joking but it's best to assume that somebody just passing by this site might get the wrong idea. What I described would be very dangerous. Among other concerns, if the bowl breaks from thermal stress then you'd have molten metal not quite as hot as the surface of the sun splattering about. Don't do it!

[Stefano]

Are there alloys with a higher melting point than tungsten?

[Andy Perrin]

Are there alloys with a higher melting point than tungsten?

Typical alloys have phase diagrams like this (from wiki):

 

You can see that it's better to have pure metals. Otherwise you get metal slush ("L+alpha" or "L+beta") of one variety or another at a lower temperature.