The Hefner lamp, or in German Hefnerkerze, is a flame lamp used in photometry

Photometry (optics)

Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power; rather, in photometry, the radiant power at each wavelength is weighted by...

 that burns amyl acetate

Amyl acetate

Amyl acetate is an organic compound and an ester with the chemical formula CH3COO[CH2]4CH3 and the molecular weight 130.19 g/mol. It has a scent similar to bananas and apples which is not detectable by all people. The compound is the condensation product of acetic acid and 1-pentanol...

.

The lamp was invented by Friedrich von Hefner-Alteneck

Friedrich von Hefner-Alteneck

Friedrich Heinrich Philipp Franz von Hefner-Alteneck was a German electrical engineer and one of the closest aides of Werner von Siemens. He is largely remembered for the invention of the Hefner lamp, which provided the measure of luminous intensity used in Germany, Austria and Scandinavia from...

 in 1884 and he proposed its use as a standard flame for photometric purposes with a luminous intensity

Luminous intensity

In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye...

 unit of the Hefnerkerze (HK). The lamp was specified as having a 40 mm flame height and an 8 mm diameter wick.

The Hefner lamp provided the German, Austrian, and Scandinavian standard for luminosity during the late nineteenth and early twentieth centuries. The unit of light intensity was defined as that produced by the lamp burning amyl acetate with a 40 mm flame height. The light unit was adopted by the German gas industry in 1890 and known as the Hefnereinheit. In 1897 it was also adopted by the Association of German Electrical Engineers under the name Hefnerkerze (HK).

Germany moved to using the New Candle (NK) from 1 July 1942 and the candela

Candela

The candela is the SI base unit of luminous intensity; that is, power emitted by a light source in a particular direction, weighted by the luminosity function . A common candle emits light with a luminous intensity of roughly one candela...

 (cd) from 1948. The HK unit is still used as a measure of the intensity of kerosene pressure lamps in Germany.

1.128 Hefnerkerze = 1.019 candela.