In the beginning the world was only lighted by the sun. During the day there was light, and at night there was darkness.
The history of night lighting goes back 10,000 years to the first records of fire-making, when light was created by the flame from cooking fires or flaming torches.
Wood, oil, kerosene and gas all came along as different fuels used for lighting, but the common thread in all was a flame that created light.
The electric powered incandescent light bulb arrived in the 1880’s and initially produced about 1.7 lumens per watt. Incandescent bulbs grew more efficient over the next 40 years, reaching nearly 15 lumens per watt by 1920
.
The ratio of light produced to electrical power consumed took on a specialized term:
Efficacy
. The word is used by the lighting industry to describe the energy efficiency of light sources, and it is seen as the measure of the lumens produced per watt (l/w or LPW).
Efficacy: A word taken from the Latin word
efficere
-for
efficient
, meaning - the having power to produce the desired result.
General Electric Company (GEC) in England developed a new light with high pressure, high temperature mercury discharges that produced a much whiter light. In 1932, GEC announced its new high pressure mercury discharge lamp, which exhibited an efficacy of 36 lumens/watt.
By 1934, GEC England had produced a prototype fluorescent lamp with an efficacy of 35 lumens/watt. This prompted a fluorescent lamp development project at General Electric in Cleveland. In April 1938, General Electric started production on the fluorescent, and early models were available that produced “warm” and “cool” light.
By 1960, the GE Research Laboratories had produced experimental lamps using sodium and thallium iodide with high efficacies and good light color properties. General Electric announced the metal-halide lamp in 1962, and used it at the 1964 World’s Fair in New York.
In 1957 General Electric, developed a new high temperature glass which was used to contain sodium plasma at high pressures. Using this new material as an arc tube, General Electric began selling High-Pressure Sodium (HPS) lamps in 1965.
In 1962, the first LED that could produce visible red light was invented at General Electric. Many more developments followed in white LED’s that created the increased efficacy seen today.
The Historical Efficacy Chart shown below of some different light sources and the improvements achieved over their lifespans. One can see from the trend of the graphs that the LED has yet to see its maximum potential of efficiency.
