Thomas Edison

Compute the power of Edison\'s DC distribution

Edison\'s 1882 Pearl Street Station in Manhattan supplied 110 V DC to about 400 light bulbs across 85 customers in lower Manhattan. To compute the system\'s power, current, and resistance, use the universal power calculator: enter 110 V and the load wattage (e.g. one of his 100 W bulbs draws 0.91 A and presents about 121 Ω resistance).

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The math behind Edison\'s incandescent lamp

Edison\'s breakthrough was a high-resistance, long-life filament that could be operated from a low-current distribution system. The physics is captured by Joule\'s law and Stefan\'s law of radiation.

Edison realised that to use a thin (efficient) filament you need it to have high resistance — so that for a given supply voltage the current stays low, the I²R loss in the supply wires is small, and one bulb does not draw enough current to dim the others on the same circuit. His carbonised-bamboo filament had a hot resistance of roughly 100 Ω, drawing about 1.1 A from the 110 V Pearl Street supply, giving 121 W per bulb. This was the design constraint that justified the entire Pearl Street system.

The radiation rises with the fourth power of temperature, so even small temperature increases vastly increase brightness. Edison\'s bamboo filaments operated near 2 600 K — high enough for usable visible light without melting (carbon sublimes near 3 800 K). Modern tungsten-filament incandescent bulbs operate near 2 800 K; LEDs achieve the same lumens with 10× less power.

Patents and authority

Edison held 1 093 US utility patents in his own name — a record at the time and not surpassed in the United States until Kia Silverbrook in the 2000s. Many of his patents are still cited; below are the most influential by impact:

• US Patent 223 898 — Electric Lamp (1880): the practical incandescent bulb with carbonised filament. The patent that established the modern lighting industry.
• US Patent 200 521 — Phonograph (1878): the first device to record and play back sound. Foundational patent for the entire recording industry.
• US Patent 369 280 — Electric Distribution System (1887): the three-wire DC distribution method that became the basis of the Pearl Street and subsequent municipal systems.
• US Patent 493 426 — Method of Manufacturing Filaments (1893): industrial-scale production of bamboo and later squirted-cellulose filaments.
• US Patent 678 722 — Storage Battery (1901): nickel-iron alkaline battery, later used in early electric vehicles and railway signalling.

Reference: Thomas Edison timeline

Edison\'s engineering method, step by step

1. Identify a real-world problem with commercial value. Edison did not invent for invention's sake. He targeted markets — telegraphy improvements, indoor lighting to replace gas lamps, recorded sound for office dictation. His patents (1 093 in his name) almost all addressed an identified market need.
2. Gather a research team and equip a laboratory. In 1876 Edison built the world's first industrial research lab at Menlo Park, New Jersey — staffed with chemists, machinists, and physicists. The "invention factory" model was itself one of his most consequential innovations: every modern corporate R&D centre traces back to Menlo Park.
3. Test exhaustively before publishing. For the incandescent light bulb (1879), Edison's team tested over 6 000 plant filaments before settling on carbonised bamboo as the most durable. The famous "I have not failed; I've just found 10 000 ways that won't work" attitude reflects systematic empirical screening, not blind trial-and-error.
4. Patent first, demonstrate publicly second. File before the public demonstration so competitors cannot copy. Edison filed US Patent 223 898 (incandescent lamp) on 4 November 1879; the public demonstration at Menlo Park was on New Year's Eve 1879. Order matters in patent priority.
5. Build the entire system, not just the device. A light bulb is useless without a generator, distribution wires, sockets, switches, meter, and billing system. Edison's 1882 Pearl Street Station in lower Manhattan delivered DC power to 85 customers from one centralised generating plant — the prototype of the modern electric utility.
6. Commercialise through your own company. Edison Electric Light Company (1878) became Edison General Electric (1890) and then merged with Thomson-Houston in 1892 to form General Electric — still one of the largest engineering companies in the world. Edison kept ownership and control, which is why the GE name dropped "Edison" but his methods stayed.

Worked example: Pearl Street Station economics

Pearl Street Station went online on 4 September 1882 with a 100 kW Jumbo dynamo (improved by Charles Brush) producing 110 V DC. It supplied 400 incandescent light bulbs across 85 customers in lower Manhattan within a 2 km radius. Compute the system load, current, and per-customer service.

The economics were brutal in 1882 — at $0.24/kWh (about $7/kWh in 2024 dollars) only the wealthiest commercial customers could afford continuous lighting. Within a decade, scale economies and competition with gas dropped the price by 80 %, and by 1900 electric lighting was affordable for middle-class urban homes. The lesson: a new technology has to demonstrate itself at any cost, then ride down the experience curve.