Incandescent light bulb granted a Hungarian patent (No. 34541) for a tungsten filament lamp that lasted longer and gave brighter light than the carbon filament. Tungsten filament lamps were first marketed by the Hungarian company Tungsram in 1904. This type is often called Tungsram-bulbs in many European countries. Filling a bulb with an inert gas such as argon or nitrogen slows down the evaporation of the tungsten filament compared to operating it in a vacuum. This allows for greater temperatures and therefore greater efficacy with less reduction in filament life. In 1906, William D. Coolidge developed a method of making "ductile tungsten" from
Phase-out of incandescent light bulbs source is similar in character to that from a Planckian "black body" in spectral distribution, that is, the bulb, as the filament heats up, produces light from wavelengths throughout the visible spectrum. Alternative light sources use phosphors or combinations of mono-chromatic LEDs (red, blue, green) to produce "white" light, giving significantly irregular spectral distributions which can result in color casts in photography and differences of color matching when compared to incandescent light or daylight. Halogen lamps are a type of incandescent lamp with improved efficiency over regular incandescent lamps. Though not as energy efficient as other alternatives, they are up