The Term "Line" for the Burner Size

Before I describe the individual burner types, I would like to explain something important at this point, namely the so-called burner size specification "line".

Right from the start, different sized burners were developed to meet people's different lighting requirements. Where one needed more light, one just had to use a larger burner with a correspondingly large wick. With low light requirement, smaller burners could be used e.g. in children's rooms at night. Therefore, there was a growing desire to link the size of the burner with an indication of the size, and this already happened with the oil burners towards the end of the 18th century! The French definition of that time has survived to our day.

Following a tradition from early times, the size of a burner is indicated in the unit of measurement "line". The term "unit of measurement" probably raises expectations too high; because "line" was unfortunately never introduced worldwide in a uniform and binding way, but was only used in continental Europe (= Europe without Great Britain) transnationally.

The Parisian "Line"

A "line" (historically more correctly called a "Parisian line") is by definition the twelfth part of the old Parisian inch (= pouce in French). A Parisian inch (not to be confused with the English inch) is exactly 27.07 mm. The twelfth part of it is 2.256 mm. You notice right away: the metric system was not yet born at that time! The "metre" as a unit of measurement was first introduced in Paris in 1799, but it took quite a while for it to become generally accepted at least in continental Europe.

The Parisian line was used as a measure of length in Europe from the 17th century until the 19th century. Consequently, it was also used to indicate the wick width of a flat wick. The flat wick was already invented by the Frenchman Léger in 1773. With the burners that followed, the wick width was decisive for the size of the burner. The wider the wick used, the wider / larger the burner had to be. At that time, the size of a burner was simply indicated by the width of the wick used in Parisian lines. For example, if a burner had a wick whose width measured 5 Parisian lines (that is approx. 11.3 mm), the size of this burner was specified simply with 5 lines.

This size specification has also been retained for the oil burners based on Argand’s principle. But since these burners did not have a simple flat wick, but a tubular wick, one had to specify their size in line after one now measured the width of the flat compressed tubular wick. The line specification was therefore not based on the entire circumference of the wick, but on half of it. That sounds a bit strange, but it becomes a bit more understandable when you think about the fact that the “line” was introduced mainly as the "size indication" of the burner and not of the wick. The line size meant the optical size of a burner, i.e. its spatial dimensions, and not its flame efficiency. And with this it becomes clear why one went over to pressing the tubular wick into a flat structure in order to measure its width, since the size of Argand’s oil burner did not differ significantly from an old-fashioned burner with the simple flat wick, if the measured widths of the flat wick and compressed tubular wicks were roughly the same. With the trick of the tubular wick pressed flat together, the line again worked satisfactorily as a measure of the external dimensions of a burner, regardless of what type of burner it was and what type of wick was used in it. In addition, the size specification was very convenient by simply measuring the width of a flat wick. You just had to squeeze the tubular wick flat to get a kind of "flat wick" again, the width of which was measured. This also explains why with the duplex burner, which burns two flat wicks parallel to each other, only the width of one wick is used as a basis for size measurement, although this burner is by definition a flat burner; because here, too, the two wicks are arranged in such a way that their spatial extension comes close to a tubular wick.

This measuring method was later retained in the more modern round burners for kerosene/paraffin lamps, which instead of a tubular wick used a normal flat wick, which, however, was transformed into a round wick in the burner. Now the width of a once folded wick had been used as a measure of the line size. For example, if a Kosmos burner used a flat wick half the width of which was 10 Parisian lines, then the size of that burner was given as 10 lines. Line is abbreviated with 3 short quotation marks (’’’). 15’’’ therefore means 15 lines. Line means ligne in French, and Linie in German.

Measurement of the line size with different burners (Upper row: The wick - Lower row: Determination of the line size)
From left: Flat wick 22 mm for 11''' flat burner (calculated 9,8''') 
Tubular wick Ø 31 mm for 20''' Veritas burner (calculated 21,5''') 
Flat wick 62 mm for 14''' Kosmos burner (calculated 13,7''')

In the next photo, three different burners are shown that have approximately the same line size. With 11''' flat burner and 10''' Kosmos burner, the purely optical size is very similar; the duplex burner, on the other hand, is much larger in appearance.

Different burners with comparable line sizes but quite different wick widths 
From left: 11''' Flat burner by R. Ditmar (wick 25 mm; calculated 11''')
10''' Kosmos burner by BJB (wick 50 mm; calculated 11''')
Duplex burner by an unknown manufacturer (2 wicks 26 mm each; calculated 11.5''')

The Burner Size of British and American Burners

Since the British replaced the simple flat burners much earlier with their epoch-making duplex burners, which were almost always the same size of around 11-12 lines, they did not need this continental European unit of measurement. The conventional duplex burners each use 2 wicks, the width of which is often 1 English inch, i.e. 25.4 mm. If you now use the Parisian line as the unit of measurement, you get about 11 lines for the burner size; the more common, slightly wider wicks of approx. 27 mm result in 12 lines. However, this size specification for duplex burners is obsolete; it is not used. Americans have always had their own sizes for burners; they have simply classified the burners in 4 different sizes characterized with the numbers 0 to 3, but that does not mean that they have created great clarity and simplification. There are a lot of exceptions. The American burner sizes are not discussed here, but in the chapter American Lamps.

In continental Europe, where an unmanageable number of different types of burners in different sizes were developed, the line as a specification of burner size was of much greater importance. The very first kerosene/paraffin burners, i.e. the flat burners had relatively smaller sizes of 2 to 11 lines. The epoch-making Kosmos burners were marketed in sizes from 6 to 18 lines. The following flame disc burners had sizes from 10 to the enormous 60 (Meteor burner by R. Ditmar) lines.

If you now expect that the size of a burner specified by the manufacturer, which is expressed in lines, can actually be traced back to the width of the wick used, you will often find that this is not always the case. With the increasing evolution of kerosene/paraffin burners towards larger burners with a flame disc, the line as the burner size has increasingly been used for a loose and rough orientation of the burner size. While the line sizes in the flat and Kosmos burners still correlate to some extent with the wick width, in the large flame disc burners they are increasingly less deducible from the width of the wicks used, since with different burners that belong to the same line size, wicks of different widths used. For example, the most common 20-line flame disc burners of the Matador type have wick widths of 80 to 95 mm, the line size of which is calculated to be 18 to 21. In the following tables I have listed the common burners with their wick sizes and calculated line sizes.

Table A: Flat burners (formula = whole wick width divided by 2.256)

Table B: Round burners with flat wicks (formula = half wick width divided by 2.256)

*) Duplex burner is not a round burner, but the space required by its two flat wicks is similar to that of a correspondingly large round burner.

Table C: Round burners with tubular wicks
(Formula = half the diameter times 3.14 and the result divided by 2.256)

The Thread Size of Burners

Of course, the size of a burner also affects the size of the collar into which it is screwed. The burner thread must reasonably follow the size of the burner. As a result, collars are also equipped with internal threads of different sizes. If you compare these thread sizes, you will find that the burner producers have succeeded in introducing an early standardization. With the Kosmos burners in particular, the standard thread sizes have been kept very consistently. For example, all 10-line Kosmos burners have the same thread size, regardless of who produced the burner or the corresponding collar. This has the enormous advantage that such standardized burners can, at least in principle, be interchanged with one another as required. Another great advantage lies in the fact that a large number of medium-sized to large burners have the same thread size of 39.5 mm. For example, the 12-, 14- and 16-line Kosmos burners and the 15 to 22-line flame disc burners have this uniform thread size, so that it is even possible to change the type and size of the burner if necessary. The British duplex burners with thread instead of bayonet fitting also have this thread size.

On the other hand, the flat burners have unfortunately their own thread sizes that do not match the Kosmos burners. An exchange between these burner types is therefore only possible if the collar on the font is also exchanged accordingly.

Table D: Thread sizes for common burners

Most of the center-draft burners are missing from this table because they are not easily interchangeable with burners from other manufacturers. The thread sizes specified above are no guarantee that burners with the same thread size can be interchanged with one another at will. The standardization that is common today, sometimes with hundredths of a millimetre accuracy, could not be achieved at the end of the 19th century. Therefore it sometimes happens that e.g. a Kosmos burner with a 39.5 mm thread size does not fit into a correspondingly large collar. Minimal deviations in the thread teeth and thread pitches are responsible for this. There is also the German peculiarity that the threads of inexpensive burners are pressed, whereas those of higher quality burners are cut.

Light Intensity of Burners

When, in the last quarter of the 19th century, ever larger, ever more powerful burners were developed, with which it was hoped to gain more market share in the competition, there was naturally also a need to classify these burners not only in terms of their optical size, but also in terms of the intensity of their light. A physical method had to be developed to measure the light intensity of the burners under standardised, constant conditions.

In the mid-1880s, the German engineer Friedrich von Hefner-Alteneck succeeded in developing an apparatus named after him to measure the intensity of light photometrically, regardless of how it was produced. Consequently, the so-called "Hefnerkerze” (translated: Hefner candle) was introduced as the unit of measured luminous intensity. Whether 1 Hefnerkerze corresponded to the luminous intensity of a precisely defined candle flame (measured under specified conditions, of course) and was therefore allowed to bear the word "candle" in its name, I do not know. It reminds me of the horsepower HP, which was probably not necessarily defined by the strength of a horse either. Be that as it may, many German burner manufacturers indicated the luminous intensity of their newly developed burners with Hefnerkerze.

In Great Britain, an older measuring system had already been established based on the luminous intensity of a precisely defined candle made of spermaceti oil (a very high-quality whale oil). The unit introduced in Great Britain was then called "candlepower" (abbreviated CP), probably also in reference to horsepower.

After a certain time, both Hefnerkerze and candlepower were replaced by the new unit called “New Candle”, which has been officially called “candela” since 1948 (abbreviated to cd) and is an international unit in SI. A normal household candle has a light intensity of around 1 cd. Hence the name of the unit (candela = candle in Latin). 1 Hefnerkerze corresponds to 0.9 candela, 1 candlepower about 0.98 candela (source: Wikipedia). Roughly simplified, you should get as much light from a kerosene/paraffin burner of, for example, 30 Hefnerkerze as from approx. 27 ordinary candles combined. However, it is an open question whether the human eye would have felt or perceived this in the same way.