This scientific paper by V.V. Kubarev investigates the physical mechanism behind "Drummond light," the dazzlingly bright white light emitted by calcium oxide (CaO) at high temperatures. Using optical emission spectroscopy and He-Ne laser backscattering, the study demonstrates that this phenomenon is a form of equilibrium thermal radiation, not luminescence as previously debated. The core finding is that calcium oxide undergoes a sharp, reversible transformation at a threshold temperature of approximately 2000 K. Below this temperature, it behaves like an ideal "white body" with very low emissivity (~0.1). Above this threshold, it transitions into an almost ideal "black body," with its emissivity increasing tenfold to nearly 1. This dramatic increase in emissivity is responsible for the sudden and intense light emission, providing a definitive physical explanation for a phenomenon known since the 19th century.
An Investigation into the Drummond Light of Calcium Oxide
The Phenomenon: Drummond light is the intense, bright white light produced when calcium oxide (CaO), or lime, is heated to very high temperatures. Its exact cause has been a subject of scientific debate for over a century.
Challenging Old Theories: The author initially investigated the light after observing it during experiments with a terahertz laser. After disproving hypotheses of optical discharge or simple fluorescence, the research focused on challenging the prevailing theory that CaO simply acts as a standard black body emitter at all high temperatures.
The Core Discovery: The paper's central conclusion is that the dazzling light is caused by a sudden change in the material's optical properties. At a critical threshold temperature of around 2000 K (approx. 1727°C or 3140°F), calcium oxide's ability to emit light (its emissivity) abruptly increases by a factor of about 10.
From White Body to Black Body: This change represents a transformation of the material's character.
Below 2000 K: CaO acts as a "white body," reflecting most radiation and emitting very little thermal light (emissivity of ~0.1).
Above 2000 K: It rapidly transforms into a near-perfect "black body," which is a highly efficient absorber and emitter of thermal radiation (emissivity approaches 1.0).
Experimental Proof: This conclusion was confirmed using two independent methods:
Emission Spectroscopy: By heating CaO with a laser and measuring the spectrum of the light it produced, researchers determined its temperature and calculated its relative emissivity, noting the sharp jump at the threshold.
Laser Backscattering: A low-power He-Ne laser was reflected off the CaO sample. As the sample was heated past 2000 K, the amount of reflected laser light dropped significantly, directly proving that the material was absorbing more and reflecting less, thus confirming the increase in emissivity.
Key Takeaway: The mystery of Drummond light is solved not by a special type of luminescence, but by a temperature-induced physical transition. This transition turns a poor thermal radiator (a white, reflective material) into an exceptionally efficient one, causing the sudden, brilliant glow.