Occasionally, when working with clients, they express surprise that one of the mainstays of infrared lamps is the classic “quartz tube” halogen bulb. It was invented in the 1950s, so it seems odd that such a relatively old design would still be preferred for modern infrared emitters. However, sometimes classic designs are still the best. Halogen bulbs have a remarkable longevity, and are unlikely to be surpassed any time soon, in terms of price vs. performance, for most industrial applications.
The Key to Halogen Bulbs’ Longevity
At heart, halogen infrared emitters are a variation on the classic incandescent light bulb which is still used around the world. Like incandescent bulbs, halogen bulbs utilize a filament made of tungsten which is super-heated to produce light, contained within an enclosure filled with inert gas.
The main differences involve the type of enclosure, and the gas within it.
Rather than glass, halogen bulbs utilize forms of quartz which are far stronger than glass – able to withstand significantly higher pressure and heat. This makes quartz casings reliable even in applications calling for several hundred degrees’ temperature.
The atmosphere within the bulb also varies. Traditional incandescent bulbs generally use a mixture of nitrogen and argon. This mixture is simply there to prevent oxidation. However, halogen bulbs use different gases like iodine or bromine, which are electronegative and held at significantly higher pressures than the gas within a traditional bulb.
This is what allows halogen infrared bulbs to often last for a thousand hours or more. When a traditional nitrogen/argon bulb burns, the tungsten filament is continuously vaporizing the outermost layers of molecules, which enter the gas and then are deposited on the inside of the glass. Therefore, when a bulb “burns out” the interior is blackened. It’s tungsten soot.
However, the gasses within a halogen bulb captures and collect these tungsten particles. Rather than depositing on the glass, they instead re-attach to the filament. In effect, the tungsten recycles itself, burning off and re-acquiring the same layers of metal repeatedly. This lengthens the lifespan of a halogen bulb by several times beyond that of a standard incandescent, while also allowing it to operate at a much higher temperature.