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Dimming low power light bulbs

Discussion in 'Electronic Basics' started by Frederick Williams, Feb 27, 2013.

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  1. I know one can dim filament bulbs with triacs (or similar).
    I think I know that one used not to be able to dim fluorescent lamps by
    the same or similar means.
    But can one dim low power lamps _of some kind_ by _some means_?
    What is a low power lamp? Is it (at present) a fluorescent lamp?

    The questions are prompted by strip lights outside a brach of Sainsburys
    that are on all day even in bright sunlight. I would have thought that
    lamps could be installed the brightness of which could be controlled (in
    an inverse fashion) by the brightness of the incident sunshine. But
    would that require the strip lights to be replaced as well?

    Please not that my knowledge of things electrical is limited.
  2. Jamie

    Jamie Guest

    When you say strip lights, it leads me to think you are talking about
    LED strip lights? If that being the case, yes, they can be regulated but
    not with a conventional voltage control unit. You need to get at the
    string of LEDs and put a current limit device in there and maybe a photo
    cell with some electronics to automate it abit.

  3. Daniel Pitts

    Daniel Pitts Guest

    A common, but by all means not the only, approach to "dimming" LED
    lights is to use PWM. The wider the pulse width, the more fully "on"
    they are. This can be quite efficiently done.

    I don't know much about TRIACS, but from what I read on wikipedia, it
    looks like using one to dim an LED strip would be reasonable.
  4. operator jay

    operator jay Guest

    Pretty much any commonly used lighting technology (incandescent, fluorescent
    (T8, T12, T5, T5HO), compact fluorescent, metal halide, LED, high pressure
    sodium, etc.) has means to do dimming. The costliness varies. Sometimes
    special 'dimming ballasts' are needed wiht the fixtures, and very often,
    special dimmers are needed. And yes, lighting can be controlled based on
    daylight (search 'daylight harvesting'). While I do not know what
    Sainsburys is (and I am assuming that 'brach' is just a typo for 'branch'),
    in a scenario with outdoor fixtures mounted on a building exterior it would
    be typical to do less intelligent controls. At least it would be typical in
    much of north america. Either photocell control, or a timeclock, or a
    combination of photocell and timeclock, might be used. The lights would
    just be turned off and on in a more or less 'dusk til dawn' manner.
    Astrological timeclocks are available that can accommodate changing
    sunrise/sunset times with the seasons, and beyond that they can be
    programmed with routines for weekdays, weeknds, holidays, and all sorts of
    stuff. And they're not that expensive.

    'Low power' may not be a well defined term, maybe 'efficient' is a better
    term (depending on what you are actually asing, of course). Certain
    technologies are more efficient than others, but if you want lots and lots
    of light out of an efficient luminaire, you still need lots of power. All
    of the lighting technologies mentioned above are OK for efficiency, except
    for incandescent which is not good for efficiency. As rough numbers, I'd
    say you can get 70 lumens per Watt to 140 lumens per Watt out of the
    efficient technologies above. Fluorescent is probably around 100, and
    widely used in normal indoor commercial applications. High pressure sodium
    and metal halide are often used outdoors, with efficiencies between say 80
    Lumens/W and 140. Incandescent is probably 10-20 lumens per watt. LED
    lighting is changing fast. There is a ton of research money and effort
    going into LED and it may well be the future of lighting. I don't think it
    is king of efficiency yet for bulk lighting, generally speaking. Though for
    some people it is the go-to technology. And the marketing hyping it is at
    times perhaps a little ... zealous.

    There are other newsgroups where you might get a better response on a
    question like this. I'm a little rusty on them but
    alt.enegineering.electrical might be one, another. I'll
    crosspost them in this reply.

  5. No, fluorescent strip lamps. The things common in commercial
    premisses. Sorry for not being clearer.
  6. Yes, those.
    That is what I was wondering. Thank you.
  7. A popular beat combo m'lud. Oh, no, sorry: a supermarket chain well
    known in the UK.
    Thank you.
  8. Dimming fluorescent lamps is not all that easy.
    The following is probably more than you want to know,

    The easist way to 'dim' a bunch of fluorescents may be to just turn
    some off.

    George H.
  9. I think I heard that some years ago, hence my question and my wondering
    whether more recent dimmer technology (or, perhaps, lamp technology)
    allowed it or made it easier.
    I'll read it. Thank you.
    I may write a letter to the shop manager to that effect.
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