Historical Context

The observation of a circadian or diurnal process in humans is mentioned in Chinese medical texts dated to around the 13th century.


Gwei-Djen Lu (2002). Mnemonic Rhyme to Aid in the Selection of Acu-points According to the Diurnal Cycle, the Day of the Month and the Season of the Year. London: Routledge. Page xx


History of the oldest light source: Candles

Although it is one of the oldest light sources, candle did not change much throughout the history. It is basically a mass of wax or some other fuel through which is embedded wick which, when lit, produces light. They are used for illumination and sometimes for heating. There is evidence that the earliest candles were made from whale fat in China during the Qin Dynasty, some 200 years B.C.

In India, about the same time, they were made from wax that was a residue of boiling cinnamon. After that many of the fuels and materials for wicks are tried. One of the most common materials people used for fuel is beeswax. It was used from 40BC in China until the discovery of synthetic materials. Those from 40BC China were made in paper molds with rice paper wicks. One of interesting variants of candle dates from 1st century and is made from a type of fish called eulachon which is nicknamed “candlefish”. During spawning, its body fat is so high that, if caught and dried, it can be lit and used as a candle.

Nomadic tribes were first to make candles in Europe during the late Roman era. Candles they made were made from tallow or animal fate because olive oil (that Romans used for lamps) was almost nonexistent in the northern regions of Europe. When Roman Empire fell, so did the amounts of olive oil that were available to the regions that were under it so the candles made from tallow spread across the Western Europe.

It was like this until the 18th century when whaling began. It was found that spermaceti, crystallized oil of sperm whale could replace tallow. It produces brighter light, it was available in great quantities and it did not produce bad smell, unlike tallow. After that, some other materials were found that didn’t include hunting of whales like: colza oil derived from turnip and oil made from rapeseed that also gave smokeless light. In 1850s, James Young refined paraffin wax by distilling coal. Paraffin wax is white wax that burns clearly, it does not have bad odor and it is cheap so it can be produced in great numbers. Because of that, it became common commodity in households.

Wick was also improved. It was made from paper, flax, hemp and cotton with different times of burning and with necessity to trim wicks to the braided cotton, wicks infused with chemicals that control speed of burning and wicks that coil when burn and with that trim themselves.

Except for lightning candles can be used as timers because they have relatively steady burning rate. Candle timers are marked on the outside with lines that represent hours (or in case really big ones - days). They can tell time if weights are imbedded at the marks. When candle burns to the mark, melted wax would release weight that would fall on a metal plate and mark the time interval with a sound.

Although not a major light source now, candles are still here as a decorative items and a light source in emergency situations. They are used for celebrations (birthdays, religious rituals), for making atmosphere (dinners and other occasions; plain, coloured and scented) and as a decor.


The first recorded observation of an endogenous circadian oscillation was by the French scientist Jean-Jacques d'Ortous de Mairan in 1729. He noted that 24-hour patterns in the movement of the leaves of the plant Mimosa pudica continued even when the plants were kept in constant darkness, in the first experiment to attempt to distinguish an endogenous clock from responses to daily stimuli.

(Endogenous substances and processes are those that originate from within an organism, tissue, or cell.)


Thomas Edison's invention of commercial lightbulbs

Historians agree that Thomas Edison was not the inventor of the electric light bulb, but he did produce the first commercially viable one. Earlier light bulbs were experimented with as far back as 1802; and there were 23 others who had invented light bulbs, some of whom were still working on them at the time of Edison’s work.

Three factors in combination are generally recognised as contributing to Edison’s success:

  1. A durable incandescent material
  2. Elimination of air from the bulb-a better vacuum
  3. A filament material of high resistance

Thomas Edison’s serious incandescent light bulb research began in 1878, filing his first patent later that year…”Improvement In Electric Lights” in October 1878. His experiments involved the fabrication and testing of many different metal filaments, including platinum. Platinum was very difficult to work with, and prone to being weakened by heating and oxygen attack.

In addition, platinum was expensive, and too low in resistance; which would require heavy copper conductors in Edison’s electric distribution system he was designing to supply commercial installations of his bulbs. This system would later become the model for our modern electric utility power distribution system of today.

By New Year’s he was demonstrating lamps using carbonized cardboard filaments to large crowds at the Menlo Park laboratory. It was not until several months after the patent was granted that Edison and his team discovered that a carbonized bamboo filament could last over 1200 hours. A year later, Edison began manufacturing commercial lamps using carbonized Japanese bamboo as filaments.

Throughout his career, Edison worked on many improvements to his signature invention, an invention that literally changed the way we live after dark. Prior to the light bulb, folks burned lamp oils or used manufactured natural gas for illumination, a rather dangerous way to provide illumination.

Electric lights became cheap, safe, and convenient to use and the public and commercial concerns installed them in rapidly increasing numbers. 




Mimosa pudica is well known for its rapid plant movement. Like a number of other plant species, it undergoes changes in leaf orientation termed "sleep" ornyctinastic movement. The foliage closes during darkness and reopens in light.

The leaves also close under various other stimuli, such as touching, warming, blowing, or shaking. These types of movements have been termed seismonastic movements. The stimulus is transmitted via action potentials to the pulvini of the plant, where contractile proteins and aquaporins induce the movement of water and electrolytes out of the cell.The movement occurs when specific regions of cells lose turgor pressure, which is the force that is applied onto the cell wall by water within the cell vacuoles and other cell contents. When the plant is disturbed, specific regions on the stems are stimulated to release chemicals, including potassium ions, which force water out of the cell vacuoles and the water diffuses out of the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole. This movement of folding inwards is energetically costly for the plant and also interferes with the process of photosynthesis.This characteristic is quite common within the Mimosoideae subfamily of the legume family, Fabaceae. The stimulus can also be transmitted to neighboring leaves. It is not known exactly why Mimosa pudica evolved this trait, but many scientists think that the plant uses its ability to shrink as a defense from herbivores. Animals may be afraid of a fast moving plant and would rather eat a less active one. Another possible explanation is that the sudden movement dislodges harmful insects.




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