You have been mislead about lightbulbs (Maurycy's blog)
You have been mislead about lightbulbs
2026-07-30
There's a story that goes something like this:
In 1925, lightbulb manufactures secretly colluded to standardized lifespans at 1,000 hours.<br>They would test each other's products to ensure compliance.
This is true.
At the time, many bulbs lasted longer than one thousand hours.
This is true.
Therefore, this was done so that people would always need to buy more light bulbs and increase their profits.
This is wrong, but it's the type of wrong that cites its sources and hides in the part you'd never think to fact check:
The assumption that a longer lasting lightbulb is a good product.
In truth, increasing the lifespan of a bulb makes it worse in every other way...<br>but people think they want a long lasting lightbulb:<br>the purpose of standardizing was to avoid a race to the bottom.
A old-school lightbulb is a rather simple device:
A thin tungsten wire (~20 μm) sealed inside a glass envelope to protect it from air.<br>When current is applied, the wire gets white hot and starts glowing.
The most important parameter of a lightbulb is how hot that wire gets:<br>this controls the peak emission wavelength (color) and brightness of the lamp.
Room temperature objects do emit light (this is how thermal cameras work),<br>but it's at the ~10 μm range instead of the 400 nm - 700 nm light that we can see.
In order to put the emission peak in the visible spectrum, the filament would need to run at ~5700 °C
... that is, the temperature of the sun .
No metal can survive these conditions:<br>Tungsten melts at "only" 3422 °C.
Filament materials:
Since it has the highest melting point of any metal, tungsten is the obvious choice for filaments.<br>However, the metal is quite brittle and drawing it into a wire isn't easy.
The first commercialized lamps used carbon filaments that were made by charring plant fibers.<br>However, the carbon would evaporate at fairly modest temperatures ~2000 °C.
Tantalum filaments were briefly produced during the 1900s, because the metal was easier to draw into a wire than tungsten.<br>This resulted in the first lightbulbs that could actually be left on at night, although these were quickly replaced with tungsten manufacturing improved.
There ware also some experiments using zirconium dioxide ceramics, which become conductive when heated.<br>These allowed lamps to operate in air (obviating the need for a vacuum pump or glass seals), but were limited by it's melting point of 2,700 °C.
Since any filament must run below it's melting point, the peak emission is always deep in the infrared.
This means that only the extreme high-energy edge of the spectrum is useful for illumination,<br>a small increase in temperature will make a lamp orders of magnitude more efficient.<br>Also, pushing the peak energy upwards allows the filament to produce shorter wavelengths:<br>resulting in something that resembles white light instead of a reddish-orange.
The snag is that when a metal is close to it's melting point, the atoms are barely holding together:
A hot tungsten filament slowly falls apart as the metal crystals slide past each other.<br>Additionally, atoms can evaporate from the surface until there's no wire left.
The rate of both of these processes increases with temperature,<br>so there's a fundamental trade off between color/efficiency and lifespan.
The lightbulb everyone always cites in the story is hanging in a California fire department.<br>It's been running nearly continuously for over 120 years and racked up over a million hours of operation.
Impressive right?
What almost no one talks about is that it's hardly even glowing!
Photo taken by Wikipedia user Rjaerial
Despite nominally being a 60 W lamp, it draws only 4 watts...<br>and is a lot dimmer than you'd expect from a 4 W lamp due to its poor efficiency.
There isn't any documentation, but in all likelihood, the bulb was made wrong and ended up with a very high filament resistance.<br>That's why it was sold for as a night light, because it wasn't usable for anything else.
Early bulbs (like that one) were handmade, and quite expensive.<br>Because of this, there were universally optimized for long lives.
This resulted in light isn't anywhere near white, and a an efficiency that was a tiny fraction of a modern incandescent lamp.<br>(which are also terrible by any objective standards)
Once the production process was automated,<br>new bulbs cost pennies, so it made sense to optimize them to actually work...<br>because long lasting bulbs cost more money to operate:
Going off modern day prices, electricity costs around 0.10 [$/kW*h], so a 60 W lamp will consume 6$ of electricity over a 1,000 hour lifespan.<br>Considering that such a lamp only costs around 3$, installing one that lasts longer but uses more power would be silly.
Case in point, despite the cartel only lasting for 14 years, non-halogen, incandescent light bulbs still last around 1,000 hours.<br>(usually...