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Fascinating Old Lamp Tech - The Carbide Lamp and Nernst Lamp
Since my childhood, I have been fascinated by different types of electric light bulbs / lamps, especially street lights that turned different shades of colour was they warmed up.  While domestic lighting mostly consisted of incandescent light bulbs since the switch from gas lighting, there were two old lighting technologies that turned out be very unusual and interesting, which I’m sure most have never heard of.  The Calcium Carbide lamp for portable and off-grid domestic gas lighting and the Nernst Lamp, an electric lamp with a replaceable filament! 

Carbide Lamp

A carbide lamp operates by water dripping on calcium carbide to produce flammable acetylene gas.  This gas flows out a nozzle and burns with a bright white light, many times brighter than candlelight without a mantle.  A portable carbide lamp has a container which the user fills with calcium carbide and an upper section with water. To operate, the user opens a valve, which lets the water drip onto the calcium carbide at a controlled rate.  The resulting gas produced is lit using a flint igniter, usually mounted inside the front reflector.  These lamps were popular with cave explorers as they ran for many hours without carrying heavy batteries and have light output that rival many modern LED torches.  Carbide lamps were also used as bicycle lights and early car headlamps due to their intense light output. 

For rural domestic lighting, room lights would have gas piping installed in much the same as a home connected to a town gas network at the time.  The main gas supply would be connected to an outside bunker which would contain a large carbide container and water supply.  The dripping water would produce and supply acetylene gas through the gas pipework and the gas outlets would be lit in each room to provide light. 

The following video by “Our Own Devices” goes into great detail on how Carbide Lamps operate:

Nernst Lamp

Back in early days of electric lighting when light bulbs had carbon filaments, the Nernst lamp was invented as an improvement by delivering improved efficiency and longer life over the bamboo and cellulose based filaments used at the time.  Instead of a carbon or wire filament, a Nernst lamp has a ceramic glower that produces incandescent light.  The ceramic glower is an insulator at room temperature and must first be heated to start conducting electricity. 

The lamp has pair of heater tubes that heat the ceramic glower and lowers its resistance.  Once the resistance falls enough, it will conduct sufficient power to self heat and the heater tubes switch off.  A wire resister ballast limits the current through the ceramic glower to prevent a thermal runaway as the ceramic glower resistance would continue to drop, drawing more power the hotter it got. 

Unlike light bulbs that have a filament operating inside a vacuum or inert gas, the ceramic glower does not oxide when exposed to air and in turn did not require a sealed outer glass bulb.  This also meant the user could replace the ceramic glower when it fused without having to replace the lamp.  One other common failure mentioned is where the heater tube or its switch would fail.  Should this happen, a workaround was use to use a match to heat the ceramic glower until it would conduct electricity and light up. 

The following website goes into detail on how the Nernst Lamp operates:

The following video by Photonicinduction shows a Nernst Lamp in operation:

Gas Discharge lighting such as older street slights and special use lamps

For anyone interesting in older street lamps and other types of gas discharge lamps, I suggest checking the following website - 

Back in the early 2000’s when I had dial-up Internet that was charged by the minute, I used to download sections of the website to pass the time reading offline.  The website also has articles covering how the popular Low Pressure Sodium, High Pressure Sodium and Mercury Vapour lamps used in street lights evolved over the years since their invention, including lamp / bulb shapes and technical details such as their wattage, lumen output, colour rendering graphs, etc.

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