The Hefner candle ( HK ) is an outdated unit of light intensity that was used in Austria, Germany and Scandinavia .
The Hefner candle is defined by the luminous flux that an amyl acetate lamp designed by the engineer Friedrich von Hefner-Alteneck , the Hefner lamp, emits in the horizontal direction with a flame height of 40 mm and a wick diameter of 8 mm.
The lighting unit was accepted by the Association of German Gas and Water Experts in 1890 as a Hefner unit and in 1897 by the Association of German Electrical Engineers under the name Hefner candle.
Until then, the light units customary in Germany were the old light unit (defined by an 83 g wax candle that burns with a flame height of 42 mm), the unit of the German Association for Gas and Water , DVGW (defined by a paraffin candle 20 mm in diameter at 50 mm flame height) and the Berlin light unit (defined by a Walrat candle with 44.5 mm flame height and a consumption of 7.77 g per hour).
The HK unit is still used today to denote gas and petroleum pressure lamps .