Candoluminescence is the term used to describe the light given off by certain materials which have been heated to incandescence and emit a larger proportion of short wavelength light than would be expected for a typical blackbody radiator. The phenomenon is noted in certain transition metal and rare earth metal oxide materials (ceramics) such as zinc oxide and cerium oxide or thorium dioxide, where some of the light from incandescence causes fluorescence of the material. Calcium oxide also has this effect which is called limelight. The cause may also be due to direct thermal excitation of metal ions in the material. Candoluminescence may also sometimes be used informally to describe any material heated to incandescence specifically by a flame. The most common examples of candoluminescence can be found in the glowing cerium/thorium (ratio of ~1:99) oxide mesh of a kerosene lamp mantle or gas mantle and in an old style Limelight.
It is not clear that a separate physical phenomenon called candoluminescence is required to explain the behavior of Welsbach mantles or limelight. Thorium oxide has very low emissivity in the near infrared and visible parts of the spectrum. Without cooling by infrared radiation, a mantle can get closer to the flame temperature than can a black body material. The higher temperature leads to higher emission levels in the visible portion of the spectrum. Cerium dioxide was made part of the mantle composition to enhance radiative cooling by the emission of visible light.