Starting after the filament
By the early 1900s the basic electric bulb existed, and the question changed from whether a lamp could work to how efficiently it could work. A bulb that turns most of its power into heat wastes electricity, and customers pay for that. Over the next century the efforts to save energy came from lamp makers, from engineers in large buildings and, in the end, from governments.
Metal filaments
The first big step was replacing carbon with metal. Makers tried osmium and tantalum around the start of the 1900s, and tungsten followed. Tungsten melts at a much higher temperature than carbon, so a tungsten filament can run hotter and give more light per unit of electricity. The difficulty was that tungsten was brittle. William Coolidge of General Electric is generally credited with developing a ductile form of tungsten that could be drawn into thin wire through wire drawing dies around 1910. Tungsten lamps became standard within a few years and were noticeably more efficient than the carbon lamps they displaced.
Further improvements came in the 1910s, when Irving Langmuir and colleagues at General Electric showed that filling the bulb with an inert gas, such as argon with some nitrogen, slowed the evaporation of the filament. A coiled filament helped as well. These changes allowed hotter, brighter lamps with longer life.
Halogen lamps
Halogen lamps, developed at General Electric in the late 1950s, added a small amount of a halogen gas such as iodine or bromine, elements from the same group of the periodic table, to a compact bulb. The halogen cycle returns evaporated tungsten to the filament, so the bulb can run hotter and last longer than an ordinary one of the same size. Halogen lamps give a bright white light and are common in the headlamps of motor cars, spotlights and projectors. They improved on the plain tungsten bulb, but they still convert most of their energy to heat.
Fluorescent lighting
Fluorescent lamps, which came into commercial use in the late 1930s, offered a more fundamental improvement. By using an electrical discharge in mercury vapor and a phosphor coating, they produced several times as much light per watt as an incandescent lamp. Their rollout was interrupted by the war years, but afterward they spread in offices, schools, stores and factories, where long hours of use made the savings clear.
Home use was slower. Tubes were long and needed special fixtures, and many people disliked the color of the light. Over time, improved phosphors offered warmer tones.
Compact fluorescent lamps
The compact fluorescent lamp (CFL) folded the tube into a spiral or set of tubes and added a built-in ballast, so it could screw into a normal socket. An engineer at General Electric, Edward Hammer, is generally credited with making a spiral prototype in the mid-1970s, though it was not produced widely at that time because of the cost of tooling. Commercial CFLs appeared in the 1980s and gradually became cheaper.
CFLs used roughly a quarter to a third of the electricity of an equivalent incandescent bulb, according to typical manufacturer comparisons, and lasted several times as long. They had drawbacks as well: a delay before reaching full brightness in some models, limited use with dimmers, and a small amount of mercury, so used lamps needed recycling rather than ordinary disposal. Many users also complained about early light quality. Opinions on CFLs differed, and results depended heavily on the model.
Efficiency standards
For most of the twentieth century, choosing a bulb was the customer’s decision. From the 2000s, governments in many countries began setting minimum efficiency requirements, motivated by electricity demand and climate concerns. In the European Union, a staged phase-out of ordinary incandescent bulbs began in 2009. In the United States, the Energy Independence and Security Act of 2007 set efficiency standards that were phased in from about 2012. Other countries, including Australia and Brazil, adopted similar measures in the same period. The details differ by country and bulb type, and some specialist lamps were exempt.
These rules did not ban light bulbs as such. They set a minimum amount of light per watt, which ordinary incandescent lamps could not meet. Halogen designs of a more efficient type filled part of the gap, CFLs filled more, and as prices dropped, LEDs filled most of the rest. Some people opposed the rules, arguing for consumer choice, and debates continued about the cost of replacing bulbs and the disposal of mercury-containing lamps.
What the standards achieved
Replacing old bulbs with efficient ones reduced the electricity needed for lighting in the countries concerned, though the size of the saving depends on how much lighting each household used and on what the lamps were replaced with. Efficient lamps also suit off-grid lighting powered by solar panels. The rules also pushed makers to improve LED products, which in turn made the next step, LED adoption, faster than it might have been. The path from the bright carbon lamp to the efficient modern bulb is a good example of a mature technology being improved gradually and then pushed by policy toward a different one.