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Light dimmers vs CFLs

Discussion in 'Electrical Engineering' started by Jeff Strickland, Apr 6, 2008.

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  1. I have installed dimmer switches throughout my house. I installed them
    20-ish years ago for a couple of reasons -- I taught my kids that they don't
    need bathroom lights on full blast just to pee, and a light on dimly while
    watching TV is better than full bright or off.

    Now that CFLs have hit the scene, and they don't like dimmer switches, I am
    left to wonder if a light on dim uses less energy. Granted there is less
    light, but we use lights on dimly far more than lights on full. I just don't
    know if a dmmed light equals lower electricity consumption.

    Thanks,
     
  2. Yeah, and LEDs do not have the environmental overhead -- mercury content --
    of CFLs..

    I heard a guy on talk radio a few weeks ago talking about his LED lights. He
    admitted they are costly today, but over time and increasing demand, the
    prices should come down. An LED light source should be damn near a
    life-of-the-home kind of purchase, meaning it should never fail. This is
    exciting stuff in the world of lighting.



     
  3. Adrian C

    Adrian C Guest

    The media will be feeding the alarming headline "LEDs contain Arsenic"
    someday soon...
     
  4. Palindrome

    Palindrome Guest

    Let's start with an undimmed 100W incandescent lamp. It uses 1 unit
    every 10 hours.

    Now dim it to give the same light output as a 60W incandescent lamp. It
    won't be as efficient as a 60W lamp, so it will use 1 unit every 14 hours.

    Now replace the dimmed 100W incandescent lamp with a 60W incandescent
    lamp on full. It will use 1 unit every 16 hours.

    Now replace the 60 W incandescent lamp with a 60 W equivalent CFL. It
    will use 1 unit every 90 hours.


    So dimming incandescent lamps does save energy. But the savings are tiny
    in comparison with fitting the correct wattage CFL.
     
  5. Guest

    | Jeff Strickland wrote:
    |>
    |> Yeah, and LEDs do not have the environmental overhead -- mercury content
    |> -- of CFLs..
    |
    | The media will be feeding the alarming headline "LEDs contain Arsenic"
    | someday soon...

    Yep ... that's sure to happen. Just write a letter to the editor telling
    people that due to this arsenic danger they need to be careful and not break
    those LED bulbs when replacing them.
     
  6. Guest

    | Jeff Strickland wrote:
    |> I have installed dimmer switches throughout my house. I installed them
    |> 20-ish years ago for a couple of reasons -- I taught my kids that they
    |> don't need bathroom lights on full blast just to pee, and a light on
    |> dimly while watching TV is better than full bright or off.
    |>
    |> Now that CFLs have hit the scene, and they don't like dimmer switches, I
    |> am left to wonder if a light on dim uses less energy. Granted there is
    |> less light, but we use lights on dimly far more than lights on full. I
    |> just don't know if a dmmed light equals lower electricity consumption.
    |>
    |
    | Let's start with an undimmed 100W incandescent lamp. It uses 1 unit
    | every 10 hours.
    |
    | Now dim it to give the same light output as a 60W incandescent lamp. It
    | won't be as efficient as a 60W lamp, so it will use 1 unit every 14 hours.
    |
    | Now replace the dimmed 100W incandescent lamp with a 60W incandescent
    | lamp on full. It will use 1 unit every 16 hours.
    |
    | Now replace the 60 W incandescent lamp with a 60 W equivalent CFL. It
    | will use 1 unit every 90 hours.
    |
    |
    | So dimming incandescent lamps does save energy. But the savings are tiny
    | in comparison with fitting the correct wattage CFL.

    But does dimming a CFL (when the dimmer and CFL are compatible) save energy?
    I hear that dimmed CFLs don't live as long.
     
  7. I can't claim to know all CFL dimming technologies, but I can't
    think of one where dimming wouldn't save energy.

    You might find that dimmable CFL's are not as efficient in the
    first place, in some cases. One type of dimming CFL uses cold
    cathode tubes, and those are not as efficient as standard
    (thermionic) cathodes tubes, particularly in short length tubes
    used in CFLs. Thermionic cathode dimmable CFLs may require extra
    circuitry to provide power to heat the cathodes when the tube
    current drops, and of course use extra power to do this heating.
    The life of a fluorescent tube depends heavily on the control
    gear and on many cases, the number of times the tube is switched
    on. For CFLs, the control gear temperature also has a significant
    effect on the control gear life -- usually it outlasts the tube,
    but at high ambient temperatures, it can fail first.

    Simply dimming a standard thermionic cathode tube is likely to
    reduce tube life. The reduced current will result in electrodes
    cooling, which creates a higher cathode fall voltage, which will
    cause electrons and ions to be accelerated to higher energy
    levels before impact with the filament, which will sputter off
    more of the filament coating, resulting in shorter life.
    However, control gear designed for dimming may provide auxilliary
    power to the filaments to counteract this. That's easier in the
    case of control gear which is fully powered and has some type of
    dimming input signal. It's harder for control gear which is
    just seeing its own supply being dimmed. So I think the bottom
    line is that it's going to depend on the quality of the control
    gear.
     
  8. James Sweet

    James Sweet Guest


    Power consumption does drop as you dim an incandescent, but not nearly as
    fast as light output, so the savings are marginal, it does provide a nice
    mood though.

    You can get dimmable CFLs, they cost more and are harder to find, and they
    tend to flicker if used exclusively on a dimmer designed for incandescents.

    I use CFLs throughout most of my house, and have halogena bulbs I got on
    sale in a few lights that are on dimmers.
     
  9. Guest

    | Power consumption does drop as you dim an incandescent, but not nearly as
    | fast as light output, so the savings are marginal, it does provide a nice
    | mood though.

    At the lower temperature, much of the "light" shifts into the infra-red.
    The total output is the same as the input, but more of it is unusable as
    visual light. This is what I dislike of dimmers.
     
  10. Adrian C

    Adrian C Guest

    I've melted parts of an LED with a soldering iron and am still here and
    am feeling dsGF G..... <CARRIER LOST AT 11000KBPS>
     
  11. Does a halogen use less energy than a regular light bulb?

    I know they get very hot, and they make loads of light, but I was not
    thinking they would be cheaper to operate. I usppose if a halogen rated ar
    50W makes as much or more light than a standard bulb rated at 100W, then
    that alone would result in an energy saving ...
     
  12. What does that mean to mere mortals?

    You are waaaay over my head on that one.
     

  13. Does that mean that as a practical matter, the light output decreases faster
    than the energy consumption? For example, I reduce 75% of the light but only
    25% of the consumption?
     
  14. Palindrome

    Palindrome Guest

    You got it.
     
  15. Palindrome

    Palindrome Guest

    It means that as you dim a lamp, a higher percentage of the light that
    comes out from it isn't visible light. It's still there - but your eyes
    can't use it.
     
  16. Palindrome

    Palindrome Guest

    A 50W halogen lamp uses the same amount of electricity as a 50W regular
    light bulb.
    Unfortunately, it doesn't make "as much or more".
     
  17. James Sweet

    James Sweet Guest


    It depends. When you run a filament hotter, as a halogen lamp allows,
    efficiency improves. As I recall, the Halogena lamps are about the same in
    regards to lumens per watt, but they look nice and last about 3x as long.
    I've never actually had one burn out, though the lights I use them in are on
    relatively little. They have the halogen capsule inside a glass outer bulb
    so they don't get any hotter than a normal lamp. Normally they're a bit
    overpriced, but Home Depot had 3-packs for 99 cents a few years ago so I
    stocked up.
     
  18. charles

    charles Guest

    From use in our village hall, I consider that a 150w halogen gives as much
    light as a 250w tungsten, but this is without using a light meter
     
  19. James Sweet

    James Sweet Guest

    That's quite optimistic.

    It's possible though that the more compact halogen lamp and superior optics
    allows more of the light to be put where you want it, which is as good as
    making more light.
     
  20. Guest

    |
    | |> On Mon, 07 Apr 2008 03:38:05 GMT James Sweet <>
    |> wrote:
    |>
    |> | Power consumption does drop as you dim an incandescent, but not nearly
    |> as
    |> | fast as light output, so the savings are marginal, it does provide a
    |> nice
    |> | mood though.
    |>
    |> At the lower temperature, much of the "light" shifts into the infra-red.
    |> The total output is the same as the input, but more of it is unusable as
    |> visual light. This is what I dislike of dimmers.
    |>
    |
    |
    | Does that mean that as a practical matter, the light output decreases faster
    | than the energy consumption? For example, I reduce 75% of the light but only
    | 25% of the consumption?

    Yes. I don't know that the exact numbers you gave are even close. The
    real formula would be more complex as it needs to account for things like
    the temperature of the filament, its resistance change, how much of the
    spectrum is usable, etc.

    If you only need the light of a 25 watt bulb, a 25 watt bulb is the most
    efficient way to do it within the confines of incandescent technology.
    You can improve on it slightly by using low-voltage halogen bulbs running
    at a higher temperature, at the desired wattage. Other technologies give
    much better efficiency at any given light output target point.

    As for dimming, LEDs are probably the least wasteful at this, when using
    a pulse width modulation. Otherwise, the best way to dim any lighting is
    "diversity switching" (which means, turn on only enough lights to meet
    the desired illumination level and leave the rest all the way off).
     
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