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CFL in ceiling fixture

Discussion in 'Lighting' started by Norris Smith, May 27, 2005.

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  1. Norris Smith

    Norris Smith Guest

    Am I likely to have heat problems in using 20W or 26W fluorescent bulbs
    in a ceiling fixture? The fixture is surface mounted 12" dia and 5"
    deep. The fixture uses two 75W incandescent bulbs and is made of metal
    and glass.

    Thanks, Norris
     
  2. I've put a 21W 2D fluorescent with separate electronic control
    gear inside a couple of fixtures that size. They are running on
    the max temperature for the control gear, so that would seem
    to be the limit. My fixtures, although designed for ceiling
    use, are actually on a wall though, which probably improves
    cooling. So I guess you might get away with one 26W CFL,
    but not two, and don't expect full quoted life at such elevated
    temperatures -- you may well get an early control gear failure.
     
  3. Probably, especially if you use two lamps and if the fixture is
    closed. But even with an open recessed fixture you would probably have
    problems.

    CFLs are life tested in free air at 25C. The general rule of thumb for
    electronics is that life is cut in half for each 10C rise in
    temperature. So, if you measure the ambient air temperature in your
    fixture with the lamps installed you can get an idea of how long they
    might last.

    On the other hand, I use a 15-watt Philips SLS lamp a desk lamp where
    the shade prevents air flow over the ballast compartment and I'm sure
    the ambient is over 25C and the SLS has lasted for at least two years
    of heavy use.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  4. Just a quick clarification (not a disagreement!)

    life is cut in half for every 10C rise OVER NOMINAL in temperature.

    and that life is actualy ballast life

    Jeff Waymouth


    {unless, of course, you want to start predicting life extensions over
    rating as the temperature runs cooler than nominal, too!)
     
  5. True, but I would not go to the extent of expecting only half the rated
    life at 35 C, 1/4 the rated life at 45 C, etc. I am under the impression
    that most failures at 25 C should be from the lamp wearing out rather than
    electronics. I expect life to decrease with increasing temperature to an
    extent less than halving per 10 degrees C until the temperature is high
    enough for failures to be mostly from the electronics.
    But once the temperature gets high enough for most failures to be from
    the electronics, I consider it reasonable for the life expectancy to half
    per 10 deggres C beyond that point.

    Meanwhile, don't underestimate how hot things get in a ceiling fixture,
    or even in any fixture enclosed at the top and sides, even if open at the
    bottom.
    I remember looking at the package of one of these, and it said that it
    was rated for use in recessed ceiling fixtures. Most CFLs don't say this.
    Last time I checked, Philips SLS being rated for use in recessed ceiling
    fixtures was only for models up to 20 watts.

    ALSO - CFLs produce more non-radiant heat than incandescents of the same
    wattage, although generally less than incandescents of the same light
    output. This is because incandescents produce plenty of IR - which
    escapes the fixture, although mostly becoming heat somewhere in the room.
    I recently got a "Raytek" remote thermometer that works by sensing
    thermal infrared, and found an 8 inch globe in mid-air to reach at its top
    (in ambient varying from 21 to 23 C):

    Incandescents:
    41 C with a 40 watt T10 (vacuum)
    59 C with a 40 watt A19 (gas filled)
    69 C with a 60 watt A19 (gas filled)
    82 C with a 100 watt A19 (gas filled)

    CFLs:
    50 C with a 20 watt spiral
    57 C with a 25 watt Philips SLS
    70 C with a 23 watt Sylvania Dulux EL (probably from having its top closer
    to the top of the globe)
    70 C with a 42 watt spiral, (presumably with the sides of the globe hotter
    than with the 23 watt Sylvania Dulux EL)

    - Don Klipstein ()
     
  6. Thanks Jeff, that is correct. And yes, I do expect that the life of
    the ballast would increase as the temperature is dropped. However, the
    life of the "wire lamp" portion of the system would stay constant.

    Vic
     

  7. A good point - and probably explains my experience with the SLS.
    I'm never sure what "rated for use in recessed ceiling fixtures"
    means. If the life is measured at 25C in free air, then it WILL be
    lower when installed in a recessed ceiling fixture. Since the life of
    many CFLs is 10,000 hours, some of these "rated for use in recessed
    fixture" CFLs have a life of 15,000 hours under standard test
    conditions and will be expected to have a life of at least 10,000
    hours in recessed fixtures.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  8. Oh dear, so I'm not the only one with a box of dismembered CFL bases.
    :)

    It's surprising that many of the CFL bases don't have even a basic form
    of ventilation. The spiral lamps do, but many don't. This may be to
    contain mini electro-explosions when things go wrong. I'm guessing it
    can't be to reduce the risk of stuff getting poked through the
    ventilation slots, since removing the lamp from it's socket reveals a
    much larger area of exposed live metalwork.

    I've got a spherical light fixture in the close where I live and drilled
    some holes in both the base of the plastic globe and the top of the
    fixture to allow air flow through the fixture. I reckon it will extend
    the life of the CFL installed in it.

    Talking about exposed live metalwork in lamp holders.... It's 2005.
    Isn't it time we started switching all lamp holders over to something
    shrouded like the GU10 base? The traditional lamp holders are very
    Victorian. There's not much else on the market that has huge chunks of
    live metal exposed for easy finger contact.
     
  9. Lampholders are the one exception allowed to violate IP2X when doing
    a PAT test of an electrical appliance.

    Whilst you can say "gosh, this must be dangerous", there simply aren't
    any significant incidents involving lampholders. If you try to put
    together a risk/cost assessment for changing to some other style, then
    you will just find it's all cost and no benefits. (Yea, I know that
    hasn't stopped our current government with the likes of Part P, etc.)
     
  10. I can tell you that when I was at GE the electrolytic caps were the
    most carefully chosen and carefully tested component in their CFLs. I
    can't describe the testing, but can say that the ratings provided by
    the manufacturers are practically worthless when you are designing a
    device to last 10,000 hours or more. All that matters are tests that
    are run to _your_ specifications.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  11. No, it is to eliminate the risk of some one poking a paper clip or
    similar device into a ventilation hole. The socket and base are
    "grandfathered". UL would not allow them if they did not already
    exist, but you cannot create any NEW hazards.
    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  12. Ooh! That sounds fun. Tell me more. :)
     
  13. David Lee

    David Lee Guest

    Clive Mitchell wrote...
    I have this bizarre mental picture of a European standard specifying the
    correct concentration of salts required for water intended for intentional
    self-electrocution.

    Actually - as EU directives go - that probably isn't so bizarre!

    David
     
  14. I didn't say that, and don't agree.
    I don't agree with this either. The data sheets from reputable
    manufacturers are usually correct, but obviously for the conditions
    under which the devices were tested. However, if your operating
    conditions are different then you will need to run your own tests. My
    specific comment was about the temperature rating of electrolytic
    capacitors, since there is often no definition of what that rating
    means - it is often not presented in the form of a specification. Data
    shown in the data sheets along with test conditions is usually
    reliable.
    Data sheets fill the full range from superficial to rather complete.
    If the data is not there it is obvious and I do applaud those
    companies that provide a more compete set of data. However, I read
    your earlier statement to mean that data that was supplied was not to
    be trusted, and I disagree with that, at least from any of the
    reputable manufacturers.
    Do you have any examples of these so-called "engineering" data sheets
    vs. the "normal" ones. And I again disagree with your assertion that
    the majority of data provided is dishonest. It is often incomplete,
    but that data that is provided is usually correct, as long as you
    understand the conditions under which the data was obtained.
    Ran tests on each production run.
    I believe that was included.
    Don't know. And I also do not know how the process works today. There
    may be a greater reliance on tests by the capacitor manufacturer
    rather then by GE.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
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