Vintage advertising letter opener-celluloid. The Humphrey inverted light bulb. An early light bulb advertisement. The inverted part seems to refer to downward hanging fixtures holding this upside down bulb. Being celluloid I would guess this opener to be from the early 1900's. Old arc lamps from this period are rare and expensive. They were replaced by incandescent bulbs.
Humphry Davy, an English chemist, invented the first electric light in 1802. After experimenting with electricity, he invented an electric battery which, when he connected wires to the battery and a piece of carbon, made the carbon glow and produce light. His invention was known as the Electric Arc lamp. However, the light did not burn long at all, making it impractical for commercial use.
Celluloid: Also known as French Ivory. Inventor John Wesley Hyatt who—in spite of professional chemists' warnings of causing an explosion—blended camphor with nitrocellulose and produced a hard, moldable substance he dubbed "celluloid." Patented in 1869, Hyatt and his brother began producing celluloid in 1871, marketing it as a substitute for expensive natural materials like ivory and tortoiseshell. It was eventually replaced by the many variations of plastics that now fill every niche of the ecosystems including us. Better living through chemistry?