Light's measure: A history of industrial photometry to 1909

The standardisation of light and photometry – A historical review

“…39,45 Harcourt then further changed the design to the 10 candle pentane argand lamp shown in Figure 4, which was finally adopted in 1898 as a legal British alternative (not replacement) for the Parliamentary Candle. 29,49 Dibdin 48 was not impressed;…”

“…28 One of the earliest recorded applications of photometry was in 1792 when Benjamin Thompson, Count Rumford, used his modification of Lambert's shadow photometer to compare lamps and fuels for a municipal workhouse in Munich. 29,30 While different fuels gave apparently comparable results, his photometric tests demonstrated clear differences. The new science of photometry was now becoming accepted as evidence for economic decisions, however until the 1830s it remained solely a choice between using Rumford's shadow photometer and Leslie's increasingly discredited thermal photometer.…”

“…13,15,33 Along with price controls, this introduced a standard gas illuminating intensity requirement (a 15 hole Argand burner with 7 inch chimney consuming 5 ft 3 /hour, to be equivalent to 12 standardised sperm candles), extended to the whole UK in 1871. 13,29,33,34 Intensity standards of 14, 16 and even 20 candles were later introduced in different regions. 35 The Metropolitan Board of Works was given the responsibility for London's supervision in the early 1860s, after which most cities in Britain that contracted for street lighting employed teams of 'Gas Examiners' under supervising 'Gas Referees' to monitor performance.…”

“…While French experts claimed good repeatability and retained it as a standard until 1948, Palaz 39 reported foreign scientists found repeating their results very difficult, being 'on a par with a candle'. 29,39 To improve the repeatability of the British standard candle, Augustus George Vernon Harcourt developed the 'Pentane Standard' burner in 1877, claiming a natural variation of just 2%. 39 This used petroleum derived pentane in a shielded burner with chimney, the pentane being vaporised before burning so no wick charring occurred.…”

“…America adopted competing standards, using the 10 candle Harcourt pentane burner for gas lighting and the Hefner lamp for electric lamps. 29,52 However the value they determined for the Hefner lamp was low at 0.88 of a British Candle and standardised in a set of incandescent lamps. [53][54][55] This resulted in an significant difference between the two American standards.…”