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Torch (flashlight) bulb voltage ratings

Discussion in 'Lighting' started by splin, Dec 4, 2003.

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  1. splin

    splin Guest

    I expect this question comes up from time to time, but can someone explain
    the voltage ratings of small bulbs?

    I want to build a voltage regulator for a cycle lamp to provide a reasonable
    compromise between output and lifetime (say 25 hours?). I understand the
    relationship between the light output and filament lifetime as the applied
    voltage varies above and below its rated value.
    However in the UK (at least) bulbs for 2 cell torches (flashlights) or cycle
    lamps are commonly available marked as 2.2, 2.3, 2.4 2.5, 2.7V and even
    2.8V. The most common seem to be 2.4 and 2.7V

    Since these are all intended for use with a nominal battery voltage of 3V
    (for new batteries), what are we to make of these ratings? Is there a
    'proper' standard for the voltage ratings or is this mostly historical and
    related to the size (and hence the internal resistance) of the zinc-chloride
    cells which used to power them before low impedance alkaline and
    rechargeable cells became commonly availabile?

    The 2.5V bulbs are .8A Philips halogen bulbs (GH-90 I think). What were they
    designed to be driven by? I'm guessing NI-Cd cells, but then they don't seem
    to be any brighter than 2.7V/.7A Krypton bulbs when also driven by 2 Ni-cd
    cells..

    Or are they all pretty much equivalent and will all have similar lifetimes
    when operated from the same type of batteries?

    Or are the bulbs designed and rated relative to the size of batteries they
    are typically used with - eg. the 2.2V prefocused bulbs seem to be typically
    used in lamps driven by 2 AA cells, which will have a rather higher internal
    resistance than a pair of D cells and thus will be exposed to a lower
    average voltage. My experience of the 2.2V bulbs is that they do have a
    rather short lifetime - a few hours at most - and thus probably are
    substantially overdriven.

    Searching on the Web it seems to rather hard to get proper lumen and
    lifetime specifications for these small bulbs. So without having to do a lot
    of experimentation/life-testing can anyone help me out? Incidentally I'm not
    restricted to using 2 cells but I am curious as to why so many different
    voltage bulbs are available.

    And finally, would a 6V/3W bulb be more or less efficient than a 2.4V/3W
    bulb (for the same lifetime)?

    Thanks in advance, splin
     
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