While many credit Edison as having “invented” the electric lamp, this is inaccurate. Sir Humphry Davy demonstrated illumination using electricity in 1809 but the glowing filament burned out within minutes. Joseph Swan experimented with various incandescent light ideas starting in 1850 but his major weakness was the lack of a perfect vacuum inside the glass envelop and his bulbs self-extinguished in a few hours.
Edison’s most significant contribution was the development of a long-burning filament material when placed in a near-perfect vacuum ensuring a bulb burned for hundreds of hours. Edison and his partners then designed the equipment and distribution infrastructure to generate electricity with water or steam power and to distribute that direct current power on a commercial scale. Edison’s electrical manufacturing operations provided wire, switches, sockets, and wiring hardware for use in residences and small businesses where his improved electric lamp could be used.
Ironically Edison’s earliest bulbs used a cotton sewing fiber strengthened by zinc chloride immersion prior to carbonization into a lamp filament. If cotton and zinc chloride sound familiar, it is because cotton rag paper immersed in zinc chloride become vulcanized fibre! Edison perfected a means to remove all of the air within the glass envelope which with his cotton, and later bamboo filaments, allowed the commercialization of electric lamps. Edison used carbonized sewing threads until 1880, after which he transitioned to Bristol board (a form of carbonized paper) resulting in lamps burning for 600 hours.
Electric lamps on vehicles started in 1898 with the Columbia Electric Car made by the Electric Vehicle Company in Hartford, CT. The main problem limiting adoption of carbon filament bulbs earlier than the 1910s was the fragile carbon filament. Heated to a near molten incandescence, filaments easily shattered when bounced about on rough dirt roads of the era. More reliable kerosene, carbide, and acetylene gas lighting systems remained the standard for automotive lighting until after 1912.
Cadillac introduced the electric starter motor requiring a generator and battery in 1912. As manufacturers had perfected more ruggedized carbon filament lamps to withstand the harsh impacts of normal driving, electric lighting quickly replaced the burning of petroleum products for automotive lighting represented by the 1913 Model 76 in the Marshall Collection. By the 1920s, auto manufacturers offered carbon-filament based electric lighting systems as standard equipment.
The C marking on the lamps indicate ‘candlepower’. The first lighting instruments were candles burning animal fats (tallow), beeswax, and similar materials. The British first established ‘candlepower’ as a unit of measure for illumination in 1860. One candlepower was defined as equivalent to the light output of a spermaceti candle made from the material found in the head cavity of sperm whales. When the kerosene lamp was designed, manufacturers needed a means to indicate how luminous the lamp was as compared to the candles in use at the time. Thus, it made sense to use of candlepower to indicate how many candles a given kerosene lamp might replace while providing an equivalent luminous intensity.
The classic railroad lantern with a flat wick (3/4”) produces about 10 candlepower (roughly a 7-watt nightlight bulb equivalent) of illumination. A round wick table lamp similar to a Rayo kerosene lamp generates approximately 80 candlepower (60-watt electric light bulb) of illumination while an Aladdin lamp with a gauze mantle that incandesces produces roughly 300 candlepower (250-watt electric light bulb). The use of ‘wattage’ with respect to light bulbs references the amount of power consumed and not the light intensity produced by the bulb.
Today the standard unit of measure replacing ‘candlepower’ is ‘candela’ both of which represent light intensity as perceived by the human eye. For scientific work both foot-candles (U.S. imperial system) and lux (European metric system) are defined as the amount of visible light that falls upon a flat plane or surface. A single foot-candle is equivalent to the amount of light that falls on a surface that is one foot away from a standard candle’s flame, and a lux is the amount of light that falls on a surface one meter away from a standard candle’s flame. For conversion, 1 foot-candle is the equivalent of 10.764 lux.
The lamp marked ‘32&31C’ indicates the bulb is a dual-filament headlight bulb producing 21 candlepower (15-watt electric light bulb equivalent) at low beam and 32 candlepower (25-watt electric light bulb equivalent) at high beam setting. The two smallest bulbs (parking, tail, or license plate lights) are 3-candlepower while the intermediate size bulb brake lamp bulb) is 15-candlepower.