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Running incandescent or halogen bulb with 2/3 or lower voltage possible?

Discussion in 'LEDs and Optoelectronics' started by Voltaic, May 25, 2015.

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  1. Voltaic

    Voltaic

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    May 6, 2015
    Can I drive a halogen or incandescent bulb with significantly lower voltage to achieve a lower colour temperature?

    I'm guessing I can with an incandescent but can I with a halogen, or will it not work properly?
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    A lower colour temperature?
    Do you mean 'Kelvin'?
    Surely, if you fit a dimmer and turn it down, the colour would change. I just tried mine and they went from bright white all the way down to a deep sunset red.
    You can buy bulbs that are 'cool white' or some diffusers do a similar job.
    DJ's do it all the time with different coloured transparent film over their par-cans.
    Can you elaborate a little more?
    Edit: forgot to say that YES, (most) incandescent and halogen bulbs can both be dimmed.
     
  3. Voltaic

    Voltaic

    82
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    May 6, 2015
    Thanks, Yes the question is if you imagine a spectrum for a halogen bulb going from infrared through visible to uv. I would like to shift the entire spectrum downwards by lowering the voltage by a fairly large amount.
    You can't really buy incandescent bulbs anymore here and I haven't had much experience with halogen but I just wanted to know if I lower the voltage with halogen to make it red like you said, it won't stop the bulb from working properly in any way?

    Putting a coloured film over would only change the visible colour, so I just want to move the whole spectrum by lowering the voltage (I don't have a halogen bulb to test yet) so I was just wondering if it would work fine.

    It sounds like it would. I read halogen bulbs have a reaction that recoats the filament, so would this still work if I turned it down until it is much lower colour temperature (ie. red)?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Halogen bulbs are pretty much the same as normal incandescent bulbs other than the halogen in the envelope allows he tungsten filament to be run at a higher temperature.

    A lower voltage to them should have the same effect as any other filament bulb.
     
  5. Voltaic

    Voltaic

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    May 6, 2015
    Ok thanks, so there's nothing that would stop the re coating reaction from working the same if I turned it down so much that it was red instead of white.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Even if it does, the halogen simply allows the filament to run hotter (where the tungsten "evaporates" faster). At a lower voltage this happens less so the halogen reaction is needed less.
     
  7. Martaine2005

    Martaine2005

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    May 12, 2015
    http://en.wikipedia.org/wiki/Halogen_lamp
    It looks like the halogen lamp would need a higher temperature for the chemical reaction to take place. So, it would work as you described. But, you would have to 'up' the voltage for the reversible effect to take place.
    Have a good read and test it..
     
  8. Voltaic

    Voltaic

    82
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    May 6, 2015
    Thanks

    So what will happen, will it just not last as long (ie. last about the same time as a non halogen bulb) or will it break very quickly?

    I ordered some cheap 12v halogen bulbs but maybe I needed standard incandescent ones.
     
    Last edited: May 25, 2015
  9. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    I have an overhead lamp fixture in my kitchen/dining area consisting of five incandescent lamps all connected to a nearby wall dimmer. At night we turn the dimmer down to minimum so as to provide a "night light" in the kitchen. Originally, this was fitted with five 40 watt, clear glass, incandescent lamps (the kind commonly found illuminating car dealer lots) and they lasted several years. Recently, replacement lamps have a halogen "capsule" inside the clear glass envelope and are made in China. The life of these lamps is very poor, lasting a few months at most. The failure mode is a broken filament, which can sometimes we "re-welded" for a short extension of life by gently shaking the fixture. I don't know what is causing the reduced life, poor quality control or increased evaporation rate of the tungsten filament caused by dimming and consequent lowering of the temperature below what is necessary to re-deposit evaporated tungsten back onto the filament. But I don't like it. Fortunately, my wife hates this particular fixture, so when I find my "round tuit" it will be replaced, probably with a dimmable LED fixture.
     

    Attached Files:

  10. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    Probably a thinner, shorter filament than is typical to save on tungsten.
     
  11. Voltaic

    Voltaic

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    May 6, 2015
    Thanks, I guess I shouldn't have ordered those halogen bulbs, oh well they were very cheap.

    It's hard to get incandescent bulbs here, shops can't sell them anymore except for a few specialty ones such as oven lights (which I am using for my salt lamp).

    I just want to create a low powered heat lamp with light (ie. 15w approx.) instead of 100w+ like the actual heat lamps sold.
     
  12. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    It just occurred to me that your 12V halogen lamps will probably work just fine as infrared heaters if you lower the voltage a LOT, which will lower both the filament temperature as well as the evaporation rate (as @(*steve*) said earlier). It's worth a try anyway. Now where to get a low-voltage, high-current source for your lamp(s)? Perhaps a salvaged microwave oven transformer, re-wound with a few turns of wire? You can experiment with the number of turns until you find the right voltage to dimly light your lamp(s).
    [​IMG]
    You do need to remove (hacksaw off) the original high-voltage secondary winding, which then leaves room to add a few turns of heavy-gauge insulated wire for your new low-voltage secondary. And make sure you "ground" the core to the power-line safety ground (NOT the Neutra!). Insert a fuse, and perhaps a switch, in series with the primary winding. There is plenty of information on the Internet on how to make the mod.
     
  13. Voltaic

    Voltaic

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    May 6, 2015
    Thanks, how much would you expect I should lower the voltage by?
    But if I lower it too much could I be in the region of eye danger, Ie. invisible infrared that can still damage your eye?
    I was hoping to just lower it until it glowed red like a heat lamp.

    I only want it as a very low powered light and heat source so I was just planning to connect the required number in series and parallel to get the right resistance with a plug pack type supply.
    10-15w total would be fine.
     
  14. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    Don't worry too much about eye damage. An incoherent source of relatively broad spectrum such as incandescent or halogen lamps will be too hot or bright in obvious ways before they're dangerous in unseen ways.

    Have you tried two 20W, 12V halogen lamps in series on a 12V supply for effect. By the way, if you want all the heat reflected forward from the lamp, you need to get the aluminum reflector type lamps or ones that mount in a metal reflector as many glass reflector lamps are dichroic, designed to project light out the front while allowing heat to pass through to the back.
     
    hevans1944 likes this.
  15. Voltaic

    Voltaic

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    May 6, 2015
    Thanks, I'll try that when the halogen light I ordered arrive in a few weeks.

    Yes I read about mirrors and the non heat reflective properties of standard mirrors.
    It will be difficult to make a reflector though, would plain aluminium foil be much too thin to work?
     
  16. BobK

    BobK

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    Jan 5, 2010
    Lowering the temperature of a filament will not produce more infrared at any frequency than the same filament as at a higher temperature. Have a look at this chart of the black body spectrum:

    [​IMG]

    You can see that lowering the temperature decreases the intensity of radiation at all frequencies. So if the halogen operated at normal voltage cannot damage your eyes, it certainly cannot damage your eyes by lowering the voltage and hence the temperature.


    Bob
     
    Merlin3189 and hevans1944 like this.
  17. Voltaic

    Voltaic

    82
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    May 6, 2015
    Thanks, you are right, however if I lowered it too much that it no longer produced much light your eyes wouldn't know if you are looking at higher than expected output including the ir.

    So I hope it works well glowing red because I wouldn't want to go any lower.
     
    Last edited: May 27, 2015
  18. BobK

    BobK

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    Jan 5, 2010
    Do you really think a halogen lamp glowing red would damage your eyes? Why don't we have millions of people with damaged eyes from halogen lamps that are glowing white and producing 1000s of times more IR than you glowing red one?

    I mean, it is good to be cautious, but you are being silly.

    Bob
     
  19. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Thin aluminum foil will probably absorb much of the infrared radiation and will become warm. A small fraction will be reflected. Astronomical telescope mirrors are often coated with a thin film of aluminum (because it is inexpensive), but astronomers don't generally worry about the infrared absorption. For infrared astronomical telescopes the mirror can be coated with a thin film of gold or another metal that does not absorb infrared as much as aluminum. The thickness of ordinary aluminum foil has no effect on the infrared absorbance.

    Your problem will not be aluminum foil... it should work just fine... but how to shape and support it behind the halogen lamps to act as a reflector. I would test one of your lamps first to find out if it does have a dichroic reflector. You should be able to feel the heat radiating from the back side if it does. If no heat radiating from the back at full brightness, then no dichroic reflector is present and you don't need the aluminum foil. OTOH, if there is a lot of heat radiating from the back side of the lamp, perhaps you could just form the aluminum foil around the back side (carefully avoiding the two filament terminals projecting from the back of the lamp) to act as a reflector. This may also help the halogen lamp maintain a higher internal temperature with reduced power input, which may make the halogen-tungsten re-deposition chemistry perform at reduced power input to the lamp. You will have to experiment to see what works for you.
     
  20. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    Ok thanks.

    I just wondered if it was glowing red + 80% infrared whether that could be bad.
    When during normal use (white) the infrared addition is a much much lower percentage as per the graph (ie. the white light + 10% infrared).
    I mean if I used several lamps running at a lower temperature rather than just one producing a total output of roughly the same as one running at full power white.
    Because your eyes can't detect and react to the ir.
    So the heating effect could be up to 80% more than your eyes automatically react to and expect, instead of just 10% more for example.

    I am being a bit overcautious maybe because I was a bit shocked realising how dangerous an ir led could be.


    Ok thanks, I didn't think foil would be sufficient, perhaps a metal bowl of some kind would be better.
     
    Last edited: May 27, 2015
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