Halogen versus LED (Part 2: The Halogen Process)

In the introduction to our discussion on the differences, features and benefits offered by halogen and LED technologies, we noticed a few advantages LED might offer over conventional halogen systems. To better understand the strengths and weaknesses of each system, we will look at the way each technology operates.

Tungsten Halogen Process

Halogen lamps produce a crisp white light that renders colors very accurately, and offers the longest life cycle within the incandescent lamp family. Traditional incandescent lamps are short lived due to the fact that the heat generated in the filament of the lamp causes the filament to evaporate. Halogens lamps operate on the tungsten halogen regenerative principle shown in Figure 1, which eliminates filament evaporation, and bulb blackening which holds the initial lumens and color temperature constant through the life of the lamp. The halogen process utilizes a tungsten filament that emits photons or visible light when heated to high temperatures. The filament is protected in a silica envelope filled with compressed gas, usually argon, krypton or xenon, along with a small amount of halogen compound, usually bromine or iodine.

Tungsten Halogen Regeneration Process
When power is applied to the lamp, tungsten particles evaporate from the filament and attach to the wall of the bulb. Halogen, at the same time, is decomposed and becomes atomic halogen.   
Atomic halogen is diffused on the bulb wall and combines with free tungsten particles, stripping the halogen from the bulb wall, and forming a transparent tungsten halide molecule.
As the temperature rises to over 500 degrees Fahrenheit on the bulb wall, tungsten halide is volatilized and circulates back to the filament.
The tungsten halide is decomposed around the filament at a high temperature, the halogen gas is released, and made available to combine with another halogen molecule, and the tungsten is re-deposited on the filament, thereby starting the process over again.

Lamp life is dependent upon the evaporation rate of the filament. The regenerative process of halogen process renews the filament when the operating temperature within the glass envelope is maintained. A slight decrease in the rated input volts, provided to the lamp, will significantly impact the tungsten halogen process. The input voltage can be affected by improper installation resulted in excess voltage drop in the feed lines, or by dimming. Dimming, resulting in operation below 60 percent of the rated operational input voltage, will result in the lamp blackening, and significantly reducing the lamp life as shown below.

Lamp life is directly proportional to the cost of operation for a lighting system, so it is even more important than the cost of the system itself. When a lamp burns out, you either have to pay someone to service the system, or you have to go to the store, buy the lamp, go back home, and replace it. This process takes about 30-40 minutes, depending on how close you are to the nearest home improvement store. If you figure your normal hourly rate, you may be paying quite a bit for that little lamp. When you add electricity to the cost of operation for your system, that little $7 dollar lamp may cost you close to $100. Opportunity cost or real cost; that's for you to decide!