50 Fun Facts About Light Bulb

How does an incandescent light bulb produce light?

The filament sits in a bulb that is either evacuated or filled with inert gas to stop it oxidising.

Roughly what share of the energy consumed by an incandescent bulb becomes visible light?

The rest is released as heat, which is why they work as heat lamps for incubators and Easy-Bake Ovens.

What is the luminous efficacy of a 120-volt incandescent bulb?

A compact fluorescent manages about 60, which is why governments have banned the old bulbs to save energy.

In 1802 Humphry Davy made incandescent light by passing current through a strip of which high-melting metal?

He used a battery of 2,000 cells in the basement of the Royal Institution; it was too dim and short-lived to be practical.

What was the first practical electric light, invented by Davy in the first decade of the 1800s?

Arc lamps burned their carbon rods fast and gave out kilowatts of light, so they suited only large spaces.

Who was granted the first patent for an incandescent lamp, in 1841, using metal wires in a vacuum bulb?

De la Rue had enclosed a coiled filament of the same costly metal in a vacuum tube the year before, but the metal's cost made it impractical.

Which country holds that Henry Woodward and Mathew Evans invented the light bulb, with an 1874 patent sold to Edison?

Their lamp used carbon rods in a nitrogen-filled glass cylinder; Edison needed their claim for lamps wired in parallel.

Joseph Swan began experimenting in 1850 with filaments made from what, sealed in an evacuated bulb?

Better vacuum pumps in the 1870s let him return to the experiments, and his lamp was in daily use in London by 1881.

Which London playhouse became the first public building lit entirely by electricity in 1881?

Swan's own house, Underhill in Gateshead, was the first in the world lit by a light bulb.

The first street in the world lit by incandescent lamps, in 1880, was Mosley Street in which English city?

The city's Literary and Philosophical Society building had been the first public building lit by electricity the year before.

How long did Edison's first successful carbon-filament test lamp burn on 22 October 1879?

His team later found a carbonised Japanese bamboo filament could last more than 1,200 hours.

Which plant material did Edison's team discover made a filament lasting over 1,200 hours?

His 1879 patent had listed cotton, linen thread, wood splints and coiled paper among the possibilities.

What was the first commercial application of Edison's incandescent lamps, in 1880?

The Oregon Railroad and Navigation Company vessel was also the first ship to carry a dynamo.

Historians credit Edison's business success less to the bulb itself than to what?

Generators, mains, feeders and parallel distribution were as vital as the lamp, which is why rivals with equally good bulbs are forgotten.

Which Black American inventor patented an improved process for making carbon filaments in 1882?

His heat-treatment reduced breakage and let filaments be moulded into shapes like Maxim's characteristic "M".

The Edison and Swan companies merged in Britain to form a firm later known by what name?

Edison opposed the merger at first but was forced to cooperate, and eventually bought out Swan's interest.

In 1883 the US Patent Office ruled Edison's lamp patents invalid as based on whose prior art?

A judge finally upheld Edison's claim for "a filament of carbon of high resistance" in 1889.

What did 2007 research conclude about Heinrich Göbel's claimed 1854 bamboo-filament bulb?

Four courts had raised doubts, but Edison's patent expired before a final ruling.

Which two men were granted the first patent for a tungsten-filament lamp, in Hungary in 1904?

The Hungarian company Tungsram marketed them the same year, and Europeans still call them Tungsram bulbs.

Which General Electric scientist developed "ductile tungsten" in 1906?

GE began selling bulbs with the ductile tungsten wire in 1911.

Why is tungsten the ideal filament metal?

It melts at 3,422 °C, and its symbol W comes from the German name Wolfram.

In 1913 Irving Langmuir found that filling a bulb with what, instead of a vacuum, doubled its efficacy?

The gas slows the evaporation of the tungsten filament; Imre Bródy later used krypton.

Marvin Pipkin's 1925 patent solved which everyday problem?

The frosted finish diffuses the glare of the bare filament.

The Phoebus cartel of 1925–1939 is commonly cited as an early example of what?

Osram, Philips, GE and others fixed prices and standardised bulb life at 1,000 hours, a figure that outlived the cartel.

The Phoebus cartel was incorporated in which city in January 1925?

It was meant to last thirty years but folded in 1939 with the outbreak of the Second World War.

The Centennial Light, the world's longest-lasting bulb, has burned almost continuously since 1901 in a fire station in which California city?

Made by the Shelby Electric Company of Ohio, it began as a 60-watt bulb and now glows like a 4-watt nightlight.

Originally rated at 60 W, the Centennial Light has dimmed to roughly the output of what?

It has been turned off only a few brief times and has its own webcam.

In the Edison screw designation E27, what does the number stand for?

Edison patented the screw base in 1881; his one-inch, seven-thread version became the E26 used in North America.

A halogen lamp is a tungsten-filament bulb whose gas fill contains a small amount of which elements?

The halogen cycle redeposits evaporated tungsten on the filament, extending its life and keeping the envelope clear.

In which year did General Electric patent the first practical halogen lamp?

The concept of cyclic redeposition of tungsten had appeared in a patent back in 1933.

Inside a fluorescent tube, an electric current excites mercury vapour to produce what?

Fluorescent lamps went on public display at the 1939 New York World's Fair.

GE engineer Edward Hammer invented the spiral compact fluorescent lamp in 1976 in response to what?

Philips brought the first screw-in CFL, the SL*18, to market in 1980.

Which French engineer, "the Edison of France", demonstrated neon tube lighting at the 1910 Paris Motor Show?

His company Air Liquide produced neon as a by-product of liquefying air, and he held a near monopoly on the signs.

Low-pressure sodium lamps, long used for street lighting, give off light of what colour?

They are highly efficient but make colour vision impossible at night.

Henry Joseph Round discovered diode electroluminescence in 1906 at which company's labs?

He saw carborundum crystals emit yellow, green, orange or blue light; the Soviet inventor Oleg Losev built a silicon carbide LED in 1927.

The earliest practical LEDs of 1962 emitted what kind of light?

The first visible-light LEDs were dim and limited to red; infrared LEDs still drive most remote controls.

Which GE scientist predicted in a 1963 Reader's Digest that his LEDs would replace Edison's bulb?

He also invented the red-light laser diode used in CD and DVD players.

Shuji Nakamura shared the 2014 Nobel Prize in Physics with Akasaki and Amano for inventing what?

Blue light partly converted to yellow by a phosphor coating is the key to white LED lighting, in production since 1993.

Nakamura developed the high-brightness gallium nitride LED while working for which Japanese company?

He has been a professor at the University of California, Santa Barbara since 1999.

By 2025, the most efficient commercially available LED lamps exceeded what luminous efficacy?

They convert more than half their input power into light, versus a tiny fraction for an incandescent.

Which Caribbean country swapped every incandescent bulb for CFLs and banned their sale in 2006-07?

The EU began its own phase-out with frosted bulbs in September 2009.

The European Commission calculates that its incandescent ban saves how much electricity a year?

That is worth 5 to 10 billion euros and cuts CO2 by 15 million tonnes annually.

Nernst's 1897 lamp, twice as efficient as carbon filaments, needed no vacuum. What glowing element did it use?

The Nernst lamp was briefly popular until metal-filament bulbs overtook it.

Before electricity, William Murdoch pioneered lighting his Cornish home in 1797 with what?

He was the first to exploit the flammability of gas for practical lighting, and gaslight ruled cities for a century.

Edison's facility, considered the first industrial research lab, was where in New Jersey?

It earned him the nickname "The Wizard of Menlo Park".

In 1840, which British scientist enclosed a coiled platinum filament in a vacuum tube and ran current through it?

Platinum's high melting point made it a natural early filament choice, but it was far too costly for commercial use.

Which Russian inventor obtained an 1874 patent for an incandescent bulb and later sold tungsten-filament rights to GE?

His 1897 US patent described filaments made of rare metals, tungsten among them.

In 1930, Hungarian Imre Bródy filled lamps with which gas instead of argon?

Production of krypton-filled lamps began at Ajka, Hungary in 1937, in a factory co-designed by physicist Egon Orowan.

Who created the first double-coil bulb, with a coiled coil tungsten filament, in 1921 for a Toshiba predecessor?

Hakunetsusha only developed a way to mass-produce coiled coil filaments by 1936.

Why are bayonet-base bulbs frequently used in automotive lamps?

Larger lamps may use either a screw base or a bayonet base with one or more contacts.