Lamp Current vs Voltage

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Joseph
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Re: Lamp Current vs Voltage

Post by Joseph » Thu Nov 11, 2004 10:54 am

I used to play with carbon rods from old carbon-zinc batteries when I was a kid. They sure do arc brightly.

hansensw
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Re: Lamp Current vs Voltage

Post by hansensw » Thu Nov 11, 2004 3:03 pm

Hi,<p>You guys are beyond my technical level skill, but I can follow most of it, due to 20+ years as an electrical contractor, and a certificate in electronics repair technology.<p>Currently, I'm designing a new landscape lighting fixture, and would greatly appreciate any thoughts, ideas, advice, suggestions, etc.<p>One of the biggest criteria for the light source, is lifespan of the light bulb. And that's what led me to this forum.<p>I've explored using LEDs (this is a high-end landscape light fixture, so the price of the LEDs could be justified) but that didn't work out. For example, while the LEDs themselves last 100,000 hrs., the transformers and regulators have much shorter lifespans, and are very specialized, thus making replacement much more difficult than replacing ordinary light bulbs. And there are other problems/obstacles which make it undesirable for this project too.<p>Fluorescent is physically too big.<p>The best option I've come across so far, is either an MR-16 or PAR36 halogen bulb (both of which are pretty common in good-quality landscape lighting anyway). But, the lifespan of those bulbs is less than I'd like (rated at about 2,000-4,000 hrs.).<p>So, now I'm exploring the idea of extending the lifespan of halogen bulbs by lowering the voltage. But after many hours of surfing the internet, I still don't have any solid conclusions on whether that can be done.<p>For example:<p>While many writers have stated that lowering the voltage extends the life of incandescent, some say it doesn't work for halogen (but I thought that halogen *is* incandescent -- doesn't "incandescent" refer to the heating up of the filament, to white-hot "incandescence"? And isn't that what happens in a halogen bulb too?)<p>Some writers have stated that dimmers which pulse the full 120v. in order to dim the bulbs, actually end up reducing bulb life. And to the best of my knowledge, that is the kind of dimmer that needs to be used on the 120v. side of a transformer. But then again, I wonder if the voltage would be smoothed out, after passing through the transformer.<p>I've seen "diode rectifiers" mentioned several times (and I am familiar with what those are) but again, they said it wasn't for halogen.<p>Bottom line, is it possible to extend the life of 12vac halogen bulbs?<p>Thanks,
LL

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Re: Lamp Current vs Voltage

Post by rshayes » Fri Nov 12, 2004 12:16 am

Another term for halogen lamps is quartz-iodine lamps. These are basically incandescent lamps designed to work at a higher filament temperature. This shifts the spectrum of the lamp to give more output in the visible region of the spectrum and increases the efficiency.<p>Conventional lamps can also be designed to run at these temperatures, but the life is short. An example is the old photoflood lamps once used for photography. Life was in the tens of hours, if that. Projection lamps also had a short life.<p>The short lifetime was due to evaporation of tungsten from the filament. This had two effects. First, it blackened the bulb and reduced the light output even if the filament did not fail. Second, the removal of tungsten from the filament would eventually cause the filament to burn out anyway.<p>Both of these problems were alleviated by using a halogen gas (usually iodine) to fill the lamp and operating the bulb at a higher temperature, hence the quartz envelope instead of glass. The high bulb temperature causes the tungsten to react with the iodine to form tungsten iodide. This evaporates and travels to the region of the filament, removing the tungsten from the bulb. This avoids blackening the bulb. When the tungsten iodide reaches the filament, the filament temperature is high enough to decompose the tungsten iodide and deposit the tungsten back on the filament. This counteracts the evaporation of tungsten from the filament and extends its life. Both processes require certain temperatures to work properly. Running a halogen bulb at a lower temperature would probably not increase the life of the bulb, since it would disrupt this regeneration process.<p>Your best bet is probably the LEDs but with the drive circuits designed for lower stress rather than low cost. Both transformers and semiconductors should be capable of tens of thousands of hours of lifetime if they are properly built and used.

hansensw
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Re: Lamp Current vs Voltage

Post by hansensw » Fri Nov 12, 2004 5:56 am

Thank you very much. That's fascinating, interesting, and very helpful.<p>Best,
LL

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Re: Lamp Current vs Voltage

Post by hansensw » Fri Nov 12, 2004 6:53 am

New info. just in...<p>Found the following from G.E. Lighting:<p>http://www.gelighting.com/na/specoem/hicalc.html<p>At the bottom of the page is a link for some (very old) software for calculating "how differences in voltage affect life, light output, and color of Halogen and Incandescent lamps." And the implication from how the software operates, is that dimming halogen has the same effect on bulb life as dimming incandescent.<p>But, I wonder if it matters *how* it's dimmed (i.e., pulsed voltage, or actually reduced voltage).<p>I've written to G.E., but can't get past the folks who cut-and-paste FAQs.

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Re: Lamp Current vs Voltage

Post by hansensw » Fri Nov 12, 2004 7:57 am

Ah, now it looks like I did get through to an engineer at GE. And it confirms what you wrote, Stephen, in contrast to what that (very old) software implicated. Here's what he wrote:<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>The type of dimmer will not matter.
Low Voltage lamps may be dimmed by reducing voltage. However, this may cause the bulbs to blacken. Note that the nature of low voltage lighting systems requires the use of fluorescent-
type dimmers. Lamp can be operated on AC or DC currents.<hr></blockquote>

John Brown
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Re: Lamp Current vs Voltage

Post by John Brown » Fri Nov 12, 2004 9:17 am

I think I remember reading somewhere, that for 12V halogen lamps, 10% overvoltage reduces lamp life by 50%, and 10% undervoltage reduces light output by 50%.
On the other hand, I could have just dreamt it (not that my having dreamt it would automatically make it false).

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Chris Smith
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Re: Lamp Current vs Voltage

Post by Chris Smith » Fri Nov 12, 2004 9:32 am

Get rid of the bulky transformer and use a cap to drop your voltage. Then Rectify it and use a resistor to balance out the current requirements of the leds. The cap is almost a “no loss” dropping device unlike transformers, and high quality caps should last a very long time.

hansensw
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Re: Lamp Current vs Voltage

Post by hansensw » Fri Nov 12, 2004 11:21 am

John Brown: according to that software I downloaded from G.E.:<p>10% overvoltage produces:
138% light output
119% efficiency
29% lamp life (!)
116% watts
104% color temperature.<p>And a 10% undervoltage produces:
70% light output
82% efficiency
400% lamp life (!)
85% watts
96% color temperature.<p>But again, that doesn't take into account the blackening that happens with halogen when it isn't operated at its rated voltage, as Stephen explained so well.<p>Chris Smith: according to Stephen, sounds like it might be possible to get "tens of thousands of hours" out of the supporting electronics. But for marketing purposes, I don't think that even that would be enough. The added cost of going with LEDs (probably around $300 for one fixture in this case) will need to have some heafty benefits to go along with it. 100,000 hour lamp life would be a big selling point. But if the associated components have to be replaced, say 3-5 times during the life of the bulb, then that ruins it. Most folks would rather change commonly available light bulbs (e.g., an MR-16 bulb) than trying to find someone who understands LED circuits to replace circuit boards.

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Chris Smith
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Re: Lamp Current vs Voltage

Post by Chris Smith » Fri Nov 12, 2004 12:36 pm

Design your own proprietary bulb holding sockets, and that way they take minutes or seconds to replace and cost pennies to make,... with thousands of percent mark up in pricing and profit for you. <p>Every one is happy because they can change a burnt out bulb, while the guts can be interchanged in seconds or minutes also. <p>The cap and diode circuit can be made for less than a buck. Then modular-ize it and package it. <p> Do the same for the other related circuitry, make them simple, make them modular, make them cheap for you,..... and well priced to move off the showroom floor.

hansensw
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Re: Lamp Current vs Voltage

Post by hansensw » Tue Nov 16, 2004 9:24 am

O.k., well, given that it's so cheap to make it, is it possible to design a circuit with redundancy, such that if one component fails, then another one takes its place? Or even just three complete units, with some sort of a sensor which would 'decide' which one to feed electricity to, and which to draw off of.

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