Patented by Kenneth P. Swanson (1909–1987) of Long Island, the Wabash Appliance Company’s blackout bulbs were common household items during World War II.
Enforced nightly blackouts theoretically defended against aerial bombing. Eliminating all ground-based electrical light denied enemy aircraft a clear target area and concealed landmarks useful for navigation. The practice also protected ships from submarine attack that might otherwise have been silhouetted as a target against the bright glow of distant city lights.
Coated with opaque paint, the bulb’s shaped base concentrated the filament’s brightness downward greatly reducing the surface area illuminated by lamps and other household light fixtures. When used in conjunction with blackout curtains, civilians could go about their daily lives during blackouts.