In a past post, we discussed calcium oxide (quicklime), a substance that has been used for different purposes throughout history. However, something that we didn’t touch upon was limelight, a popular way to illuminate theater stages in the Nineteenth Century.
Limelight was discovered in the early 1820s, when English inventor Goldsworthy Gurney developed a blowpipe that burned hydrogen and oxygen to produce a small, but extremely high temperature flame. When he directed this flame towards calcium oxide, it emitted an aggressive white light. Such a thing was possible due to the high melting point of quicklime at 2572°C. This allowed the substance to emit light from the rapid vibration of atoms that resulted from the rising heat without wearing away at its physical structure.
The first practical use of limelight was carried out by Thomas Drummond, who was such a major pioneer of the white light that it is sometimes referred to as “Drummond’s Light”. He used it as a means to see in the often dark and stormy mountainous peaks atop Ireland’s mountains, the location of his surveying project at the time. With a limelight at the top of a mountain, Drummond reported that he could see the illumination from as far as 68 miles away.
After this time, limelight became common in theaters, first appearing in 1837. Such a pronounced light was highly desirable in theaters prior to this time, since the main source of light generally came from dim gaslights that were abundant on stage for visibility, creating some profound fire hazards. With the more powerful white light, it took fewer limelights, each consisting of a blowpipe with a quicklime cylinder at the end of the flame, to light up the theater. Traditionally, there was one limelight for the main stage, while others were used for purposes specific to the show, such as simulating sunlight and moonlight.
However, limelight, while better than past methods of stage lighting, was not without its challenges. One major downside was that each light needed continuous monitoring, with a worker adjusting the block of lime as it burned. In addition, while the amount of limelights on and around the stage was limited, they each still contained an open flame, posing a fire risk during every show, especially for the worker who had to operate in close contact with the extremely hot flame.
Of course, none of this mattered after Thomas Edison produced the first practical light bulb in 1879. By the Twentieth Century, practically all limelights fell out of use in theaters throughout the world. Even though electric lighting became the standard in virtually all facets of society, people continued to use the expression “in the limelight”, referring to someone being the center of attention.
While it’s unnecessary to expose it to a flame for illumination today, quicklime does serve some practical industrial uses because of its high melting point. Specifically, it is used in iron and steelmaking, in which it is added to the furnaces to remove impurities from the produced metal. It is especially effective in removing phosphorus, sulfur, and silica, and, to a lesser extent, manganese.
As for the theater, electric luminaires provide the performance and entertainment industries with lighting far superior to that ever granted by burning a white cylinder, with the variety of lighting types granting sufficient illumination or effects. Standards for the efficient and safe use of these lights are written and published by the Entertainment Services and Technology Association (ESTA). These documents include: