A Halo of Tungsten

"Are Halogen light bulbs better than the old incandescent bulbs?"

In many ways yes, it depends on what you consider by "better". They are fundamentally the same. Halogen bulbs are actually Halogen-Tungsten bulbs and work on the same premise as ordinary tungsten bulbs, a black body object. That basically means the hotter the filament of tungsten becomes, the faster the atoms move, the more light they kick out.  If you have not yet checked out No Love for Tungsten, it is explained in more detail.

"So what's the difference?" 

Simply put they are brighter and can last longer than a regular bulb. 

"Why?"

Think of it this way; imagine taking 20 kindergarten kids to a dinosaur museum with ONE supervisor. Very quickly, one by one, those little ones will be off running all over those exhibits, out of control with no way to get them back! That's a regular incandescent bulb. Now image the same 20 kids with 10 supervisors. As one pops out of the line to climb up the T-Rex's tail, there is a supervisor to get them back in line. The tour is more enjoyable, more efficient and will last much longer before you're kicked out of the museum. Well that is a halogen bulb; it has got some help to keep things running more efficient and longer. 

Instead of just having an inert gas in the bulb to prevent the filament from burning up they have a halogen vapour (supervisors) as well, iodine or bromine. Halogens are the 17th group on the periodic table (ahhhhh, high school chemistry flashbacks!). As the tungsten filament heats up, atoms of tungsten will pop off the filament one by one. In a regular incandescent bulb this will eventually weaken the filament causing it to burn out so they have to operate at a lower temperature to slow down this process. 

The halogen vapor creates a halogen-cycle. Essentially when the tungsten atoms pop off, the halogen causes a reaction that will cause the tungsten to redeposit and preserve the filament increasing it's life span, doubling it compared to incandescent bulbs. This allows the bulb to operate at a much higher temperature (the higher temperature facilitates the halogen-cycle in the first place). 

Now this not only extends the bulbs life BUT also creates a brighter, more SUN like light. This is what makes halogen-tungsten bulbs so appealing in use in photography, automobile headlamps, and kitchen lighting. As discussed in No Love for Tungsten, as the filament gets hotter, the faster the atoms oscillate and the brighter the light is produced. A halogen bulb has a more complete light spectrum (rainbow) of light than a regular incandescent bulb because it operates at such a high temperatures, above 2750 °C / 5000 °F. It creates a much brighter and whiter light (more blues and violets), more sun like, but that means its more sun like. These bulbs do produce some UV light, which can be damaging to fabrics and artwork and so they are encased in quartz and not regular glass to absorb the UV rays. They are then also enclosed behind a second piece of glass to protect against the high temperature of the quartz glass, which can cause a fire.

In the clip below, as the tungsten filament heats up the color shifts form a cooler, warm orange/yellow to a hotter brilliant white, enclosed behind the quartz glass. The external glass is simply for show and is far cooler than the internal quartz chamber.

This intense light is perfect for driving at night or when you need more natural or high quality light like in a kitchen for preparing food etc. Halogen-Tungsten bulbs are more efficient than incandescent bulbs and can be manufactured in very small sizes to produce very bright light form an extremely compact design. Because of their need to run at high temperatures to replenish the tungsten filament, using halogen bulbs with a dimmer switch will shorten their lifespan if run for extend periods at a lower setting.

Next week we will go spirally with CFL bulbs. Think of Kramer's levels, the key to efficiency. 

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