Earlier this summer, a group of wellwishers assembled inside Livermore, California’s fire station #6 to sing “Happy Birthday” to a light bulb. While not the most expected recipient of well wishes, anything that’s survived for 125 years deserves a celebration. Unfortunately, the Centennial Light’s impressiveness is often overshadowed by a decades’ old conspiracy theory based on half-truths and a misunderstanding of physics.

Although light bulbs are everyday items today, they were once only available as handmade luxury items. Artisans working for 19th century manufacturers like Ohio’s Shelby Electric Company optimized their products to ensure the longest lifespans. Despite the care required to make them, the early incandescent light bulbs relied on pretty basic principles—a thin tungsten wire sealed inside an airproof glass encasement glows white-hot after receiving an electric current.

There’s an issue to this setup, however. Heat dictates an object’s brightness and its peak emission wavelength, which is seen as visible color by the human eye. To achieve a peak visible emission, tungsten needs to reach a temperature of around 5,700 degrees Celsius (10,292 degrees Fahrenheit). For reference, that’s about the temperature as the surface of the sun. The hurdle is even more insurmountable given tungsten’s melting point of about 6,192 degrees Fahrenheit. This means any filament’s peak emission must fall within the infrared spectrum, whose wavelengths are longer than visible light but shorter than microwaves.

Shorter wavelengths make whiter, brighter visible light, so only small temperature increases improve a light bulb’s overall efficiency. But the hotter the filament gets, the more its atoms evaporate as the metal deteriorates. Knowing this, early light bulbs were all about balancing brightness and efficiency with lifespan.

So how has the Centennial Light lasted for 125 years, and how did it get wrapped up in a conspiracy theory? To answer that, it’s best to understand the allegedly nefarious plot concocted by a group known as the Phoebus Cartel. In all fairness, the Phoebus Cartel was a very real entity formed by international companies including Phillips and General Electric in 1925 who aimed to control the rapidly expanding incandescent light market. The cartel managed to accomplish this through a mixture of price-fixing and famously establishing a standardized 1,000-hour lifespan across its light bulbs. Although the Phoebus Cartel disbanded about 14 years later amid the outset of World War II, its standardized lifespan remained a benchmark for decades.

Critics often cite the Centennial Light and its over one million hours of near-continuous illumination as an example of how sturdy and well-made light bulbs once were prior to the rise of “planned obsolescence” manufacturing–but it’s not that simple. The fire station’s antique is ostensibly a 60W bulb, but it actually only draws four watts of power—and even then, it’s dimmer than a usual 4W light thanks to its inefficiency. According to electronics and software blogger Maurycy, the likely explanation is that someone at Shelby Electric Company accidentally crafted a handmade bulb with a ridiculously high filament resistance, and subsequently sold it as a night light.

Instead of proving conspiracy theorists correct, the Centennial Light actually offers a case study of why manufacturers adopted certain standards that still influence today’s products. Classic incandescent light bulbs hypothetically could burn for a very long time, but they’d offer such a dim output that no one would want to buy them. Promising a 1,000-hour lifespan ensured everyone benefited from uniformly bright, similarly long-lasting bulbs that didn’t cost a fortune in electricity bills. In reality, the only reason the Centennial Light made it this far is because its glow is barely visible.

Meanwhile, technological progress also pokes holes in the conspiracy theory. Companies eventually moved away from incandescent lights to fluorescent and LED options, largely because those are even cheaper, longer lasting, and more reliable.

Have big businesses engaged in shady tactics to line their pockets throughout history? Absolutely. However, light bulbs simply aren’t the clearest example of planned obsolescence.