Why is 12V Xenon so much more common than 120V Xenon?

[fpbear]

While looking for a decent quality puck light, I noticed something peculiar. 12V Xenon fixtures and bulbs are much more common than the 120V versions. I find this very puzzling because the 12V Xenons require a transformer which costs the manufacturer more money to produce, and the transformer can burn out. So why would more companies want to produce the 12V rather than the 120V? Why would more people buy them? I tried to research this myself, and the best answer I could come up with is that the 12V might have a higher color temp as it burns hotter, and the filament is tougher to withstand vibrations. But is that it? Could that explain why people want to add a bulky and failure prone transformer to something that could otherwise be a simpler and more compact 120V device?

 

[Anders Hoveland]

Xenon gas adds more to efficiency at lower wattages. That is the reason why they never bothered filling household incandescent bulbs with krypton, though that is beginning to change in some instances.
Incandescent filaments designed to run on lower voltages typically last longer, so filling it with a xenon makes more sense here. A small improvement may not be worth the added cost if the bulb only lasts 750 hours.
Filaments designed to run on lower voltages last longer, because the filament must be thicker to maintain the same resistance for any given wattage. If the filament lasts longer, that means that the filament can be further designed to run at a slightly higher color temperature, resulting in whiter light (at least than it would otherwise have) and (moderately) higher efficiency. This is achieved by making the filament slightly a shorter, with an accompanying small decrease in width to maintain the same resistance value.
A thicker filament takes longer for the tungsten to evaporate off and form a defect. Once a tiny defect begins to form on the filament, it is a chain reaction, since the cross section becomes lower, and this becomes a choke point of the current passing through, further evaporating faster than the rest of the filament length. But you are right, a transformer is not ideal, typically there will be loses of 10-15%, though this is apparently outweighed by the benefits of running the bulb at a lower voltage. If you were wondering, the reason they do not use low voltage in electrical outlets is because of variable voltage drop in the long wires leading from the transformer to the outlets in your house. Lower wattage filaments tend to have a lower color temperature, which is why 12v xenon is used in these pucklights, to keep the light from being too orangish and dull.

 

[MichaelW]

Or to prevent electrocution hazard.

 

[fpbear]

That is an interesting explanation Anders! I noticed that the 120V xenon lights I'm trying out are a much warmer color temp compared to halogen. To my eyes the xenons seem more like 2500K, warmer than 2700K. So the 12V version must be closer to 2700K if it's a slightly higher color temp. I suspect the biggest motivation for manufacturers to produce more in the low voltage variety is to make the bulbs tougher with the thicker filament. They don't want customers to return the fixture because the bulb filament broke during shipping. I doubt that electrocution has much to do with it (although it's a minor plus for 12V), since there are so many 120V compact fluorescent bulbs and people are generally not afraid of Edison sockets. The warm color temp of the 120V xenon reminds me of the kind of light you'd get from a room completely filled with candles, so if one desires lighting with excellent color rendition plus the warmest color temp it looks like 120V xenon would be best for that.

 

[Anders Hoveland]

What is misleading is that they claim xenon has a "brilliantwhite light". Then consumers buy it and find the light a little dull. Xenon is whiter – just whiter than it would be if it did not have xenon. Xenon has an interesting effect, not only does it reduce heat conduction away from thefilament, but the high molecular weight of the xenon gas prevents the tungstenfrom evaporating, even more so than krypton or argon. So keeping the filamentdesign constant, the addition of xenon will both lead to a slightly higher colortemperature AND longer life.
Any time you have a 20 watt incandescent filament, the light is not exactly going to be "brilliant white". This is one of the disadvantagesof incandescent, and yet another reason why LED may be more advantageous forsmall lighting applications.
What I mean is that for lower wattage filaments, they typically design the filament to be a little longer than a higher wattagefilament so it can also be a little thicker. This also reduces the temperatureof the filament a little, since the heat resistance is being spread over alarger area, which further helps lengthen lifespan, compensating for thesmaller diameter filament.
It just makes sense to use xenon with puck lighting. Anotheradvantage of xenon is that, because of its lower heat conductivity, and thesmall bulb size, it helps keep the glass from becoming too hot, which couldotherwise become a safety hazard. Xenon is not some magical gas, however, it isjust better than krypton or argon, but also more expensive to use.

 

[N8N]

Lower voltage incans are more efficient in terms of lumens per watt than higher voltage ones (to a point; at very low voltages they can't make the filaments thick enough, this is why you never see a single cell incan flashlight.)

 

[fpbear]

Is there a difference in dimming performance between a 20W 120V xenon and 12V xenon? Suppose it is dimmed very low, at 10% for some candle light mood effect lighting and it is kept at that dimming position for a long time. How is the performance at these different voltage xenons at such a setting?

 

[idleprocess]

I have seen a lot of accent and track lighting with exposed conductors using 12V. In addition to safety, this makes for a certain design aesthetic. In a retail or restaurant environment, it's easily reconfigured for a new seasonal display or remodel. With a beefy enough transformer, adding more lights is easily done via connecting additional fixtures without needing to add more power or run more wiring.

 

[idleprocess]

Lower voltage incans are more efficient in terms of lumens per watt than higher voltage ones (to a point; at very low voltages they can't make the filaments thick enough, this is why you never see a single cell incan flashlight.)

Witness the glory that was the maglite solitaire ... managed both less brightness and runtime than a coin-cell LED light! In my experience, they even manged worse color rendition...