When introducing Planck's switch to looking at black-body radiation, a number of sources -- like MinutePhysics, the Economist, random online encyclopaedias and even here on HSM.SE (plus many popular history accounts: 1, 2, 3, 4, etc.) -- propose motivations analogous to the following:

In 1894, Planck had been commissioned by electricity companies to discover how to generate the greatest luminosity from light bulbs with the minimum energy.

Depending on the source, it is a single company, a local company, a consortium, or the government. But I haven't traced any of these mentions to an actual historical reference or document. Nor have I seen mentions of particular companies.

The above story also rings several alarm bells:

  • Why commission a theoretical physicist for an engineering problem if there are several other well-qualified experimentalists (say Lummer or others at the Physikalisch-Technische Bundesanstalt) in Berlin that could be commissioned instead?
  • More reputable accounts (like Helge Kragh's (pdf)) do not mention light bulb companies but suggest that Planck was motivated by the universality of Kirchhoff's law of black body radiation. That law was introduced in 1859, before incandescent light-bulbs were important. This suggests that the motivation for studying black body radiation, in general, had little to do with light bulbs (although we can use those theories now to think about them).
  • Tying the previous two points together: Planck seems to have been much more concerned about universal, abstract, and foundational questions and doesn't seem like the kind of character that would take on a clearly practical chore like making light bulbs more energy efficient (even if they were all the rage at that time).


Did light bulbs directly motivate Planck? Was he provided funding in 1894-1900 by anybody related to light bulbs? Were researchers close to him (like Lummer, Rubens, or Wien) motivated by making incandescent light bulbs more efficient? Or even by measuring their efficiency?

Or is this simply one of the many myths made up after-the-fact by history textbooks? (If so, bonus question: who originated it?)


The most convincing story that I've found so far in this direction is on the wikipedia page for the Physikalisch-Technische Bundesanstalt:

The first outstanding scientific achievement at the PTR was also closely connected with Max Planck. To decide whether electricity or gas would be more economic for street lighting in Berlin, the PTR was to develop a more precise standard for luminous intensity. For this purpose, in 1895, Otto Lummer and Wilhelm Wien developed the first cavity radiator for the practical generation of thermal radiation.

But this is again stated without a reliable reference. Jorg Hollandt's article in this collection (pdf) might be able to corraborate the above story, but I cannot read German to verify.

  • $\begingroup$ Please accept one of the answers. $\endgroup$ – Martin Schröder Jul 10 '17 at 13:17

Sounds like we're all on the same page. But FWIW: In all my research for that Planck book (2015), I found no evidence that he was commissioned, contracted or paid by light bulb (or similar) companies in the 1890's for his theoretical work. Please note I'm not a proper historian, but I did, for instance, go through a number of German historical works on the topic (at embarrassingly glacial pace), including those of Dr. Dieter Hoffmann. Unless I missed something in those sources (always possible), Planck was simply working as a theoretical physicist exploiting ample state-of-the-art data arising in his own backyard. His switch in 1894, as far as I can tell, had more to do with wanting to explore something new, (after success in physical chemistry), especially after writing pieces to commemorate the recently departed titans Helmholtz and Hertz, (and especially after rereading Hertz's work on EM radiation). He opted for thermal radiation. In any case, I'm not sure light bulb companies would have cared much for Planck's work or really any pure theoretical work. Barely any physicists cared about his work at the time, from what I could tell. :-) He did later claim the obscurity of his 1890's work a godsend in that he had freedom and time without anyone competing or looking over his shoulder to make sense of it. Cheers.

  • 2
    $\begingroup$ Thank you for posting, we are in great need of expert contributions! Did you happen to see papers of Lummer, Pringsheim, Rubens, Paschen, and Kurlbaum from around 1894? I am curious if any of them worked on measuring filament emissions or at least cited incandescent bulbs as motivation. $\endgroup$ – Conifold Dec 7 '16 at 19:19

After looking into more reputable sources it seems that the "commissioned by electricity companies" is a confabulation, and the "commissioned by the German Bureau of Standards" is closer to the truth but still a huge stretch.

In Kuhn's Black-Body Theory and the Quantum Discontinuity, 1894-1912, which devotes two chapters to Planck's motivations, the light bulbs are mentioned only once:

But quantitatively it [Michelson's law] was not very satisfactory, a fact soon emphasized by H. F. Weber (1843-1912) of the Zurich Technische Hochschule, a physicist currently engaged in measuring the emission spectrum from carbon filament lamps. After criticizing the theoretical basis of Michelson's derivation (including its reliance on the Stefan-Boltzmann law), Weber proposed an alternate formula based on his own and other experiments. (...) When Wien, five years later, published the displacement law, his only reference to experiment was through Weber's law. (...) As a product of theory, the Wien distribution law had, of course, little authority until Planck rederived it by a very different route in 1899.

But Brown's Planck: Driven by Vision, Broken by War gives an earlier connection.

Beyond the University of Berlin physicists, the nearby Physikalisch-Technische Reichsanstalt hosted a number of experimenters busily studying thermal radiation. The PTR, or Reichsanstalt in more commonplace parlance essentially functioned as a bureau of standards like today's National Institute of Standards and Technology in America. The focus there was applied technology, so why on earth would their lab scientists look into obscure issues of thermal radiation? They simply hoped to design a better electric light. (...)

Berlin, and particularly the Reichsanstalt, happened to house the world's foremost experts in measuring thermal radiation. These were men such as Lummer, Pringsheim, Rubens, Paschen, and Kurlbaum. Although Planck was much more of a pencil and equation physicist than these colleagues, he shared a great deal with them.

If I had to guess the anecdote might have developed something like this: first Planck got "absorbed" by association into the Reichsanstalt crowd, which was perhaps motivated by improving light bulbs, then the Reichsanstalt was renamed into the better sounding German Bureau of Standards, which after all it essentially was, and finally somebody speculated that electric companies leaned on the Reichsanstalt concerning the bulbs (which may or may not be true), and decided to short-circuit it all the way back to Planck, for greater effect.

The reality is vaguer and messier. The interests of the Reichsanstalt experimenters regarding light bulbs apparently influenced Planck's choice of topic in 1894, although it also dovetailed nicely with his interest in thermodynamics, and Wien's law of 1893, which rederived by Planck in 1899 became one of the major stepping stones to his law, was in its turn motivated by Weber's study of light bulbs in 1888. So the light bulbs were somewhat in the mix, albeit indirectly, and we can at best credit the industrial revolution with creating a research environment that led to a major discovery in fundamental physics.

  • $\begingroup$ "They simply hoped to design a better electric light." Would you take that part of the quote as authoritative? I've been hoping to find some sort of "mission statement" for the PTR (since they published them) that confirms this but to no avail. I've read Dieter Hoffmann's "On the Experimental Context of Planck's Foundation of Quantum Theory" and it talks at length about PTR and other experimental work in quantum 'prehistory' but still no mentions of light bulbs just that in 1885/6 they aimed "to provide an absolute intensity standard" (which is a purely metrological concern). $\endgroup$ – Artem Kaznatcheev Dec 6 '16 at 7:40
  • $\begingroup$ @ArtemKaznatcheev No, there were too many "helpful" interpolations in this story, and this sounds like Brown's. Kuhn mentions Paschen among "a number of young experimentalists" who followed up on Weber's and Wien's work by improving instruments for emission measurements in 1893-96. I'd like to also check papers by other people Brown mentions but that will take some time. $\endgroup$ – Conifold Dec 6 '16 at 18:30

Other answers made it clear that “commissioned Max Planck” is likely a stretch although Siemens, owner of the oldest German light bulb factory (Siemens & Halske), did heavily fund Berlin physics (e.g. co-founded the Reichsanstalt and gave it land).

I wonder if the story could be rooted in conflation of Planck with his engineer brother Adalbert (Adelbert?) who did work for Siemens. (This might be checkable in the Siemens-Akten-Archiv.)


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