Right now, a pack of six standard 60 watt incandescent light bulbs will cost you about $15 on Amazon. If you want something a bit more special (say bulbs connected to Thomas Edison) it’s going to cost you—a lot.

On Dec. 3, 2016, a set of five light bulbs (two designed by Edison) and one socket sold at auction for $30,000 in Dallas. On their website, Heritage Auctions (the auctioneer) states the collection was used in patent infringement lawsuits filed by the Edison Electric Light Co. in the late 19th century.

Contrary to popular belief, Thomas Edison did not invent the incandescent light. However, he did make various improvements to the design, which made the invention practical for commercial use and was a granted a patent for them on Jan. 27, 1880. In the succeeding years, various companies producing and selling bulbs created under other patents began multiple lawsuits against Edison, attempting to void the inventor’s patent.

In an interview with Radio-Canada, Heritage Auction’s consignment director Don Ackerman explained why the bulbs fetched such a high price.

“The light bulbs, by themselves, if they weren't associated with the lawsuits, they probably wouldn't have much value," Ackerman said.

Ackerman explained that the original Edison bulbs from 1880 are very rare and are potentially worth $40,000. However, the bulbs and the socket in this collection date from around the time of the trial—1893.

“The Edison bulb here that we had, just the Edison bulb by itself, if it didn't have the court label on it, it's probably about a $500 U.S. item. That's where the value was — that value wasn't so much in the light bulbs but in the little pieces of paper that were attached to the light bulbs!”                                                     

Another lot related to the 1893 lawsuits—Heinrich Goebel’s patent case archive—was sold for $23,750. The Heritage Auctions’ website states that the items were used as part of the “Goebel Defense.” Goebel, who claimed to have designed the first practical light bulb in 1854, was a key witness for lawyers trying to invalidate Edison’s 1880 patent.  

The lot includes one of Goebel’s light bulbs, a cabinet card circa 1893 depicting Goebel's storefront in Manhattan, a four-page typed report from 1882 titled "The Goebel Incandescent Light" and a 36-page manuscript biography of Edison, undated and unsigned, but written during Edison's lifetime, of a laudatory nature.

Heritage Auctions also sold a collection of keys to Edison’s Menlo Park laboratory for $10,625. Matted and framed, the collection includes six keys—five with tags labeled: “of Motor Shed Menlo Park, N.J.” (two keys), “Shop Menlo,” “Laboratory Menlo Park N.J.,” and “small building containing motor and car. Menlo Park N.J.”—and a circular metal seal of the “Edison Machine Works Incorporated 1886.”

All of these items came to the consignor through the estate of his great aunt Anna Knudsen who was married to John C. Rowe, a patent attorney for Eaton, Lewis and Rowe, the law firm that represented Edison in various patent infringement cases.

A final Edison-related item from another consignor, the inventor’s hat, sold for $10,937.50.