[...]... entrance, and must have needed a fairly reliable source of artificial light for both creation and viewing The light probably came from burning animal fat such as tallow, held in a bowl and drawn up a wick made from vegetable fibres Man-made light sources for religious rituals are mentioned in the Old Testament books of Exodus (chapters 25 and 37) and Numbers (chapters 4 and 8) The early history of candles... visible light as the same power supplied to a GLS lamp, or 600 times the light from a single candle There are two disadvantages: they need additional circuitry to get started; and they emit light at only a small number of discrete wavelengths Low-pressure sodium-vapour lamps create light very efficiently and so are often used for street lighting They emit light at only two wavelengths (589.0 and 589.6... art, religion and science Furthermore, our species has developed an impressive ability to create artificial light for its own purposes, both practical and recreational Other animals are able to create light, but we shall leave that topic until chapter 7, and concentrate our attention on humans Ancient artefacts indicate the importance of the natural cycles of light and darkness in the lives and thoughts... visible light but produce a range of visible wavelengths 13 LIGHT AND DARK Figure 1.5 Spectra from electrical discharges in mercury vapour At low pressure the light output is concentrated within a narrow wavelength band in the ultraviolet At higher pressure the emission shifts to a set of narrow bands within the ultraviolet and visible ranges, shown here by the broken line In contrast, an incandescent... be simply too dark; but light has also long been linked to leisure and cultural activities The simple contrast between light and dark fascinated a number of painters including Leonardo da Vinci (1452– 1519), Caravaggio (1573–1610), Georges de la Tour (1593–1652) and Rembrandt (1606–1669) There is a style of painting known as chiaroscuro, a term derived from the Italian adjectives chiaro (light, bright... By 1882 the lamps were being produced in substantial numbers, and lawyers were delighted by the prospect of costly legal disputes about patent rights However in Britain litigation gave way to a merger forming the Edison and Swan United Electric Light Company in 1883 9 LIGHT AND DARK The filament is a fine wire made of a refractory material and enclosed in an inert atmosphere in a glass bulb to protect... surface 1.2 Wonder and worship Some underground-dwelling creatures, such as earthworms and naked mole rats, have no functional eyes To them it is immaterial whether it is day or night, summer or winter In contrast, most other animals are strongly influenced by daily and annual variations in the amount of light Homo sapiens is affected and also intrigued by the patterns of light and dark, which feature... words, e 17 LIGHT AND DARK music and light without visible performers This art form retained its French name as it spread across Europe, being seen in Greenwich in 1957 and in Athens in 1959 Son-et-lumi`re later found its e way to other continents, being presented at the pyramids at Giza in 1961, in Philadelphia in 1962 and at the Red Fort in Delhi in 1965 The culmination of the use of artificial light in... efficiently For example, the illumination from two 11 LIGHT AND DARK Figure 1.4 Output from ordinary household electric light bulbs The data points correspond to tungsten filament bulbs widely available in shops and supermarkets The continuous line and the vertical axis on the left describe the brightness as perceived by an average human eye The broken line and the vertical axis on the right show how efficiently... the Sun and the Moon, either in characteristics or in grammar Arabs perceive the Sun to be feminine and the Moon to be masculine In French the Sun is le soleil and the Moon is la lune In German the genders are reversed, the Sun being die Sonne and the Moon der Mond 1.3 Artificial illumination 1.3.1 Light from combustion In both the practicalities of daily existence and the attempts to understand life’s . 70 LIGHT AND DARK 4.3 The start of the year 72 4.4 Lunar and other calendars 73 4.5 Time zones 77 4.6 The International Date Line 80 5 LIGHT AND THE ATMOSPHERE 84 5.1 Scattered light and twilight. in certain moving black -and- white patterns and has some ability to identify polar- ized light. Patterns of light and dark are not always natural phenomena to be observed and enjoyed. Human ingenuity. daily and annual varia- tions in the amount of light. Homo sapiens is affected and also in- trigued by the patterns of light and dark, which feature in human thoughts about art, religion and science.