Short answers, pulled from the story.
An electric light, lamp, or light bulb is an electrical device that produces light from electricity, and it is the most common form of artificial lighting. The three main categories are incandescent lamps, which heat a filament white-hot, gas-discharge lamps, which drive an electric arc through a gas, and LED lamps, which move electrons across a band gap in a semiconductor.
In 1840, Warren de la Rue enclosed a platinum coil in a vacuum tube and passed current through it, creating one of the world's first electric light bulbs. The platinum design worked well but was too costly for commercial use. In the late 1870s and 1880s, Joseph Swan in the United Kingdom and Thomas Edison in the United States independently developed functional incandescent lamps.
The first practical LED arrived in 1962 and could only display deep red. The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994, which led to the first white LED using a phosphor coating. In 2009, Philips introduced the first lamps designed to replace standard 60-watt Edison screw fixture bulbs.
Incandescent bulbs are highly inefficient, emitting just 2 to 5 percent of their energy as usable light and losing the remaining 95 percent as heat. A worldwide phase-out occurred in the first decades of the twenty-first century, driven by government regulation and consumer preference for higher efficiency and longer life. The European Commission estimated in 2012 that a complete ban would add 5 to 10 billion euros to the economy and save 15 billion metric tonnes of carbon dioxide emissions.
Fluorescent lamps use a glass tube containing mercury vapour or argon at low pressure, where electricity makes the gases give off ultraviolet energy that strikes phosphors coating the tube to produce visible light. They typically use about one-quarter to one-third the power of an incandescent for the same light. Their luminous efficacy runs 50 to 100 lumens per watt, and because they contain mercury, many are classified as hazardous waste.
The most efficient source of electric light is the low-pressure sodium lamp. It produces an almost monochromatic orange-yellow light, so it is generally reserved for outdoor public lighting. Astronomers favour it because the light pollution it generates can be easily filtered, unlike broadband or continuous spectra.