Although light bulbs are everyday items today, they were once only available as handmade luxury items. 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. So how has the Centennial Light lasted for 125 years, and how did it get wrapped up in a conspiracy theory? 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.