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Light dimmers vs CFLs

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

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  1. Guest

    |
    | |>
    |>
    |> |>>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,
    |>>
    |>>
    |>
    |>
    |> 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.
    |>
    |
    | Does a halogen use less energy than a regular light bulb?

    A 60-watt bulb uses less energy than a 75-watt bulb when both are on
    for the same period of time.

    A 60-watt bulb left on for 4 minutes uses less energy than a 60-watt
    bulb left on for 5 minutes.

    What a halogen bulb does is run hotter. It uses a halogen gas mixture to
    reduce the effect of the hotter temperature on the filament. This works
    better when using low voltage. This means the filament is thicker and is
    thus better able to last a reasonable period of time at an even higher
    temperature.

    At the higher temperature, more of the emitted spectrum is within the
    range of visible light. So you can run a slightly smaller wattage to
    get the same level of visible light. So in this way it gives you the
    opportunity to use less energy.

    Halogen bulbs depend on the higher temperature to maintain the gas cycling
    within the bulb. At a lower temperature, this gas cycling quits, and the
    filament does not get evaporation return at the proper rate. You end up
    with metal depositing on the inside of the bulb (which reduces light level)
    and a shorter filament life.

    The best way to "dim" halogens, or just about any other light, is to use
    "diversity switching". That is, use multiple smaller bulbs and switch on
    only as many as needed to achieve the desired light output.
     
  2. Guest

    |
    | |> In article <[email protected]>,
    |>
    |>> 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,
    |>
    |> As you dim incandescent lamps, the conversion efficiency drops very
    |> rapidly. There is the Boltzman stating that emission goes as the fourth
    |> power of the absolute temperature. Moreover, the low proportion of
    |> visible radiation compared to total radiation gets diminished further.
    |> This is a consequence of the black body radiation spectrum with
    |> tempertature.
    |>
    |> Bill
    |
    | What does that mean to mere mortals?
    |
    | You are waaaay over my head on that one.

    The light output from an incandescent filament is based on thermal emission
    of a "black body" radiation source. This kind of emission is a very broad
    spectrum that includes infra-red (lots of it for a common incandescent bulb)
    and ultraviolet, as well as the visible light we seek.

    The black body emission spectrum is broad, but is centered on a specific
    wavelength based on the temperature. If the temperature goes lower, the
    center (and largest portion) of emission shifts to a longer wavelength.

    A 75-watt bulb using 75-watts of power is emitting 75-watts of power in its
    radiation and convective heat. The problem is _most_ of that radiation is
    in the form of infra-red. The center is already in the infra-red region
    even at normal operation. The light portion is just on the edge of the
    shorter wavelength portion being emitted.

    If you dim that 75-watt bulb, the center wavelength shifts even more into
    the infra-red, as well as reducing the total power level. So while that
    bulb may now be using only 50 watts of power and emitting 50 watts of
    power, a smaller proportion of the now lower total emission power is in
    the light spectrum.

    I'll guess at some figures to illustrate my point. That 75-watt bulb could
    be emitting 15 watts of power in the visible light portion of the spectrum.
    When it is reduced to 2/3 power, you might think that now you are getting
    10 watts of power in the visible spectrum. But due to that wavelength shift
    it's really more like 7 watts of power. Virtually all of the remainder is
    infra-red and waste heat.

    In contrast to this, halogen bulbs run at a higher temperature that shifts
    the spectrum to more of the visible range. It's still emitting more heat
    than light, but at least the balance is a better ratio of light to heat
    than in a conventional incandescent bulb. One factor to consider in this
    is that shift also means more ultraviolet. Given the need to use quartz
    for the halogen bulb due to the operating temperature, you also lose the
    filtering of UV that the glass previously performed. This is dealt with
    by having a glass cover over the bulb (but enough away from it to avoid
    the higher temperature), or in some cases an integrated bulb with glass
    outside and quartz inside. NEVER operate a halogen bulb without the glass
    covering.

    Stuff to read:

    http://en.wikipedia.org/wiki/Halogen_lamp
    http://en.wikipedia.org/wiki/Thermal_radiation
    http://en.wikipedia.org/wiki/Black_body
    http://en.wikipedia.org/wiki/Stefan-Boltzmann_law
     
  3. Guest

    | In article <[email protected]>,
    |
    |> > As you dim incandescent lamps, the conversion efficiency drops very
    |> > rapidly. There is the Boltzman stating that emission goes as the fourth
    |> > power of the absolute temperature. Moreover, the low proportion of
    |> > visible radiation compared to total radiation gets diminished further.
    |> > This is a consequence of the black body radiation spectrum with
    |> > tempertature.
    |> >
    |> > Bill
    |>
    |> What does that mean to mere mortals?
    |>
    |
    | Sorry about that, but we have to start somewhere. I am not going to try
    | hard to educate you.
    |
    | Consider a heater such as a cone heater or a toaster, Run it at low
    | voltage. It can still get hot (do not touch it). It uses up power
    | without providing any light. Get it hotter, and it will emit some
    | visible light.

    I did a fun little experiment once. I blocked out all the light going
    into my kitchen. I then turned on one stovetop burner and adjusted it to
    the hottest level where I could not quite see the low red glow from it.
    Then I photographed it widely bracketed on 2 different black & white films
    plus infra-red film (also the B&W type). The kitchen was entirely dark
    when the photos were taken (on tripod, no flash). The burner barely showed
    up on the regular B&W films on the longer exposures, and was bright on the
    IR film at the longer exposures. All were developed with 2 stop push.
     
  4. The halogen cycle *also* keeps the quartz bulb clear, by scavenging
    tungsten that gets evaporated onto it. So the lamp's initial light
    output is maintained until it dies entirely. With conventional
    incandescents, tungsten evaporates from the filament, deposits on the
    inside of the bulb, and stays there - where it slowly reduces light
    output during the life of the bulb.

    Dave
     
  5. James Sweet

    James Sweet Guest

    Yeah the lack of darkening is also a significant advantage.

    Wow, I just realized how awful my spelling was on my last reply, yikes,
    monday morning fingers.
     
  6. charles

    charles Guest

    just remember, if you're old enough, how much brighter halogen car
    headlamps are than the old tungsten ones.
     
  7. Guest

    This raises a question. Is there a CFL or LED equivelent of the
    3-level incandescent bulbs? The ones I'm thinking of generally
    have 2 filaments and the lamp base switch can turn on each individually
    or both. They come in various configurations, like 25-50-75, 50-100-150,
    30-60-90. Seems like a natural for a CFL equivelent, but I have not
    seen any.

    Bill Ranck
    Blacksburg, Va.
     
  8. Guest

    On Mon, 7 Apr 2008 20:12:07 +0000 (UTC) wrote:

    | wrote:
    |
    |> 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).
    |
    | This raises a question. Is there a CFL or LED equivelent of the
    | 3-level incandescent bulbs? The ones I'm thinking of generally
    | have 2 filaments and the lamp base switch can turn on each individually
    | or both. They come in various configurations, like 25-50-75, 50-100-150,
    | 30-60-90. Seems like a natural for a CFL equivelent, but I have not
    | seen any.

    I have seen one. It was a couple years ago. It had a warning on it
    "for use only in 3-way lamps". I don't remember the wattage levels.
    Given the warning, I wonder if it somehow using a common ballast circuit
    for both bulbs.
     
  9. Guest

    I would assume it was more to do with the contact arrangement. I'm pretty
    sure the incandescents versions say the same thing. If the 2 contacts on
    the bottom both connect it only just lights up both filaments, and I'm
    assuming a CFL version would have 2 tubes.

    Bill Ranck
    Blacksburg, Va.
     
  10. James Sweet

    James Sweet Guest



    3-way CFL and circline fluorescents are readily available, they tend to be
    rather bulky though.
     
  11. James Sweet

    James Sweet Guest


    Base shell is common, button on the bottom is for the high wattage filament
    and the extra ring is for low wattage filament.

    CFLs of two designs are available, one has a large tube and a small tube,
    the more common type has just one tube and a 3 level ballast.
     
  12. I just pulled numbers out of my ass to try and illustrate the point. I
    understand that the real numbers are likely to be far different.

    The problem is, I need 25W or less when the TV is on, but to read the paper
    I need the full wattage of the bulb. A light bulb is designed for a single
    use in mind, but the real world is that there are multiple uses. I am using
    a dimmer to try and fit into the real world.

    I was hoping that a dimmer would provide energy savings, but it seems that
    there is no real saving to be realized from this method. I get a wider range
    of light intensity, and that meets my demand. I don't get any significant
    energy savings though. Oh well ...
     
  13. James Sweet

    James Sweet Guest


    There *are* savings, it just isn't as much as one might assume. The cost to
    run one light isn't much anyway, and in the winter, the heat is useful. If
    you really want to save energy, use multiple lights. A low wattage lamp for
    your subdued light TV watching and higher wattage CFL for general
    illumination when you need it. When you want dimmed warm light, nothing out
    there yet beats some form of incandescent light. You can dim fluorescent
    lamps with special ballasts, but the color tends to shift towards yucky
    while incandescent shifts toward pleasing fire light.
     
  14. Guest

    |> On Mon, 7 Apr 2008 20:12:07 +0000 (UTC) wrote:
    |
    |> | This raises a question. Is there a CFL or LED equivelent of the
    |> | 3-level incandescent bulbs? The ones I'm thinking of generally
    |
    |> I have seen one. It was a couple years ago. It had a warning on it
    |> "for use only in 3-way lamps". I don't remember the wattage levels.
    |> Given the warning, I wonder if it somehow using a common ballast circuit
    |> for both bulbs.
    |
    | I would assume it was more to do with the contact arrangement. I'm pretty
    | sure the incandescents versions say the same thing. If the 2 contacts on
    | the bottom both connect it only just lights up both filaments, and I'm
    | assuming a CFL version would have 2 tubes.

    The incandescent versions do not say such a thing. Some say intended for
    use in a 3-way lamp. The CFL version seemed to imply there was a hazard
    in using it in a non-3-way lamp. I have used a 3-way bulb in a non-3-way
    lamp with no problem. Only one filament lit up. Still, this makes no
    sense since a non-3-way lamp will only appear to the bulb or CFL as a
    3-way one with the extra connection in the off state.

    OTOH, if the extra contact were to connect to the base in a non-3-way
    lamp, instead of the center, it may be doing something to the circuitry
    inside that could cause a problem. If the TWO ballast circuits are
    sharing something such that it is back-energizing the extra contact when
    only the main contact is turned on, then that contacted shorted to the
    base may effectively short out the CFL and cause a problem (anywhere
    from mis-operation, to device failure, to extended hazards such as a
    short circuit to the electric supply or a catastrophic device failure).

    Maybe someone who has disassembled these before and knows how to recognize
    the circuitry can get one of the 3-way ones and take it apart to see what
    it is really doing.

    There were 3 identical tubes of the long-upside-down-U shape at 120 degree
    angles (the kind I'm afraid to screw in for fear of shearing them off).
    I presume 1 was used for low, other 2 for medium, and all 3 for high. It
    could have been, for example, a 50/100/150 watt-equivalent one.
     
  15. Guest

    | Base shell is common, button on the bottom is for the high wattage filament
    | and the extra ring is for low wattage filament.
    |
    | CFLs of two designs are available, one has a large tube and a small tube,
    | the more common type has just one tube and a 3 level ballast.

    So what if it is a 3-level ballast type, and the extra ring contacts the
    base in a non-3-way socket? Would that cause a problem? I cannot envision
    (yet) how a 3-level ballast would be wired. Would it merely not operate in
    such a condition, or would there be a failure? Catastrophic failure?
     
  16. Guest

    | In article <>,
    | wrote:
    |
    |> I did a fun little experiment once. I blocked out all the light going
    |> into my kitchen. I then turned on one stovetop burner and adjusted it to
    |> the hottest level where I could not quite see the low red glow from it.
    |> Then I photographed it widely bracketed on 2 different black & white films
    |> plus infra-red film (also the B&W type). The kitchen was entirely dark
    |> when the photos were taken (on tripod, no flash). The burner barely showed
    |> up on the regular B&W films on the longer exposures, and was bright on the
    |> IR film at the longer exposures. All were developed with 2 stop push.
    |
    | Interesting. The flame is not a black body radiator. It would be
    | interesting to know if the infrared radiation from the flame was
    | primarily black body radiation as opposed to emission molecular emission
    | from the reaction products.

    It was an electric stove with the thick spiral burner elements.


    | Infrared film as well as green and red sensitive film) is made by adding
    | dyes that absorb the wavelengths in question. Astronomers used to go
    | through heroic measures to get sensitivity out to 1.4?m. With
    | semiconductor cameras, all that is much easier.

    And there are not so many good dyes available for the IR range. So they
    have to do with what few there are. IR film is more expensive and has a
    low sensitivity to treat it as (but not exactly a light equivalent). I
    have gotten good photos using a special push developer that gave me 2 stops
    of push with reduced contrast. It's been a couple decades and I have
    forgotten the name of it. It involved a special two-step procedure to
    pre-soak the film in bath A, which is only part of the developer. Then
    in bath B, the second chemical completes the process of making a developer
    work. But at this point the amount of chemical A is limited to what is in
    the film. It will deplete faster in more exposed areas, and continue to
    be there in less exposed areas to develop them even more. This has the
    effect of reducing contrast, which otherwise makes push processing a bad
    thing to do. In another experiment I managed to to push Tri-X film FIVE
    stops to about ASA 6400, and got usable pictures out of it (Kodak has
    since produced an even faster B&W film that I never got a chance to try
    with this developer). The IR film just went too grainy after about 3
    stops pushing. But that developer otherwise did quite well with IR film
    and I used it on most of the 20 rolls I played with. I need to get the
    camera back out and try again sometime.

    Electronic cameras these days do have a filter over the CCD surface that
    blocks IR. There are a couple small business that will for a price do a
    replacement of that filter for you on certain major cameras (the Canon
    one I am considering is one of them, but I won't do that one on the first
    one I get since it impacts the color on everything you shoot with it.
     
  17. Don Kelly

    Don Kelly Guest

    ----------------------------
    I don't think that he was talking about a flame-but an electric stove
    element.
     
  18. Guest

    | In article <>,
    | wrote:
    |
    |> I'll guess at some figures to illustrate my point. That 75-watt bulb could
    |> be emitting 15 watts of power in the visible light portion of the spectrum.
    |> When it is reduced to 2/3 power, you might think that now you are getting
    |> 10 watts of power in the visible spectrum. But due to that wavelength shift
    |> it's really more like 7 watts of power. Virtually all of the remainder is
    |> infra-red and waste heat.
    |
    | All in all, I liked your explanation.
    |
    | Your talking point guess, however, is way off of actuality. I just
    | looked at a package of 23W CFL's. It claims the same light output as
    | that of a 100W incandescent lamp--1600 lumens. IIRC it really should be
    | a bit more,maybe 1800 lumens. At peak eye sensitivity in the green, one
    | watt is about 650 lumens. Thus 1800 lumens would be about 2.8W. It then
    | is clear that most of the radiation will beat wavelengths that are much
    | less visible.

    Wow! It's way worse than I guessed.
     
  19. Guest

    | wrote:
    |
    |> Electronic cameras these days do have a filter over the CCD surface that
    |> blocks IR. There are a couple small business that will for a price do a
    |> replacement of that filter for you on certain major cameras (the Canon
    |> one I am considering is one of them, but I won't do that one on the first
    |> one I get since it impacts the color on everything you shoot with it.
    |
    | I assume you could put an IR absorbing filter over the lens to fix that.

    You could. I have not seen any such filters in camera lens mounts.


    | I've worked with IR films, but mainly just for special visual effects.
    | I did a lot of color work, from the early Dufaycolor through Ectacrome,
    | using films from 4X5 to 35mm. I still have a Canon A1 and a Speed
    | Graphic, but haven't even used them lately. A color printer sure beats
    | the half dozen solutions I used to make color prints.

    The only color processing I ever did was Cibachrome. And some of the high
    end professional printers can now do just as well as that (in the many
    thousands of dollars price range).
     
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