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lumens vs.watts?

Discussion in 'Electronic Design' started by [email protected], Aug 24, 2007.

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  1. Guest

    Is there a conversion or equivilant for a 12 volt,4 watt bulb that I
    cannot find? All the bulbs now seem to be rated in lumens (eg. 25
    lumens). I would like to find one that is the same brightness as the
    original 4 watt bulb. The 25 lumens about half as bright as the
    original but I cannot find any bulbs in this size with more lumens ! !
  2. Phil Allison

    Phil Allison Guest


    ** You need to identify the original bulb correctly, it may be a special

    For example, Halogen or QI bulbs are brighter than standard ones.

    Operating voltage has a big effect too - most so called 12 volt bulbs are
    rated for automotive use at 14 volts.

    Brightness and lifespan are interchangeable, if you apply more volts to a
    blub it will be brighter but for a shorter time.

    ........ Phil
  3. Nobody

    Nobody Guest

    The lumen is a measure of visible light output, weighted according to the
    sensitivity of the human eye, while the Watt is a measure of total power.

    The relationship between the two depends upon what proportion of the power
    is emitted as visible light, and which wavelengths. This depends upon the
    type of bulb and the voltage (e.g. a 110V, 100W tungsten filament bulb
    tends to produce more lumens than a similar 240V, 100W bulb).
  4. Phil Allison

    Phil Allison Guest

    "Nobrain & nobody TROLL "

    ** Irrelevant.

    ** So applying more voltage produces less light ???

    The simplest bot could do a better job of cribbing drivel like this from

    ......... Phil
  5. Bob Myers

    Bob Myers Guest

    The two units don't convert directly - "lumens"
    is a measure of the amount of light (specifically,
    the amount of luminous flux, which is a measure
    of the perceived power of the light source), while
    the "watt" measurement only gives the total power
    dissipated by the bulb (a great deal of which becomes
    heat, not visible light). You have to know the
    luminous efficacy of the bulb, or at least the typical
    efficacy for that technology, to even begin to get
    from watts to lumens. For instance, incandescent
    bulbs (which are among the poorest technologies
    in this regard - they're popular mostly because they're
    cheap and have a pretty decent color) are typically
    in the 5-18 lm/W range. A 25 lumen, 4W bulb is
    just a bit above 6 lm/W, not bad for a low-wattage
    incandescent but certainly not outstanding either.
    You could likely do far better, for instance, with an
    LED "bulb," if you can find one with a compatible

    Bob M.
  6. Nobody

    Nobody Guest

    When someone asks how to convert between lumens and Watts, the fact
    they're measuring different things is quite relevant.
    Remember that they're both rated at 100W at their specified voltage. This
    isn't a case of applying 240V to a 110V bulb.

    240V bulbs tend to have a lower filament temperature, hence slightly more
    of the power is emitted as infra-red and less as visible light.
  7. Gareth

    Gareth Guest

    Yes, because the higher voltage bulb has a higher resistance the
    filament has to be longer and/or thinner, it is therefore mechanically
    weaker and cannot be run as hot.

  8. Phil Allison

    Phil Allison Guest


    ** Was never asked for - fuckwit.

    ** YOU are an Gooogling IDIOT

    PISS OFF !~!!

    ........ Phil

  9. FWIW I was perusing light bulbs at the local Home Despot the other day
    & I noticed, sitting right next to each other, two bulbs, both
    incandescant, same wattage rating but different lumen ratings- by
    about 25-30% IIRC.


  10. If they are both standard incandescent lamps, the lower lumen one is
    a longer life bulb.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  11. Rich Grise

    Rich Grise Guest

    Was one of them "long-life" or "heavy duty?"

  12. Tam/WB2TT

    Tam/WB2TT Guest

    I recall high end photographic slide projectors used to have 24 V bulbs.


  13. Now that you mention it I do believe that was the case-

  14. Not quite, higher design voltage makes a filament longer and thinner and
    for a given wattage and life expectancy, the longer thinner filament is
    less efficient.

    - Don Klipstein ()
  15. This is rather common.

    1. One lamp may have a design life expectancy of 750 hours and the other
    may have a design life expectancy of 3500 or 5000 hours. This alone could
    make one have luminous efficacy about 15% more than the other.

    2. One lamp may be a 120V one with a coiled-coil filament with
    "visible overall length" about 25 mm, and the other may be a 120V one with
    a singly coiled filament with "visible overall length" maybe 40 mm and a
    smaller "overall diameter", along with multiple filament supports to
    improve resistance to mechanical shock and vibration. The filament with
    longer, thinner overall dimensions has a thinner "boundary layer" of hot
    gas between the filament and surrounding cooler gas, and the temperature
    gradient in the gas adjacent to the filament would be greater. This means
    more heat conduction from the filament to the surrounding gas.
    In addition, the filament supports will conduct a bit of heat from the
    These factors could mean a 10-15% difference in overall luminous
    efficacy, more in lamps of lowest current design to be able to be designed
    for better efficiency with a fill gas than with a vacuum (probably
    somewhere around .2 amp for most lamps designed for 12 volts or more).

    3. One lamp may be of higher quality than the other.

    All of these factors combined can make quite a difference. A 100 watt
    120V 750 hour lamp of a "Big 3" brand and with a coiled-coil filament is
    typically rated to produce 1710-1750 lumens.
    A 100 watt 120V 1000 hour off-brand one with a singly coiled
    multi-supported filament and made by a lower price
    "lower-than-Big-3-quality" Chinese manufacturer may be rated to produce
    1100 lumens.

    4. Lower design voltage for a given wattage and life expectancy means a
    shorter, thicker filament. The thicker filament can be operated at a
    slightly higher temperature for the same life expectancy. The thicker
    filament has less heat conduction loss per unit area by fill gas as
    explained in #2 above.
    Decreasing the design voltage increases luminous efficacy until the
    filament gets so short and thick that heat conduction through the ends of
    the filament becomes a really significant loss. Among 100 watt lamps,
    the design voltage that maximizes overall luminous efficacy tends to be
    a little over 12 volts (with a singly coiled filament).
    I look among "100A" (100 watt "medium screw base" "regular
    lightbulb shape and size" incandescent lamps in my "Philips catalog"
    ("SAG-100" printed 9/99), and the 12 volt version is rated to have an
    average life expectancy of 1,000 hours and to produce 2050 lumens.
    The 34 volt version is rated to produce 1940 lumens (1000 hours).
    The 230V version is rated to produce 1270 lumens (1000 hours).
    The 277 volt version is rated to produce 1070 lumens (1000 hours).

    Various 120-130 volt versions are rated to produce 1560-1730 lumens
    if designed to last 750 hours.

    5. Halogen version makes a little difference - the bulb of a halogen
    lamp is much more compact (since the halogen cycle allows a much more
    compact bulb by keeping it clean of condensed tungsten vapor) and the
    fill gas pressure is much higher because of a smaller sturdier bulb made
    of tougher material. This along with the halogen cycle achieves longer
    filament life and also a slight increase in filament temperature.
    The Philips "Halogena" 100 watt 120V version produces 1670 lumens while
    achieving a life expectancy of 3000 hours.

    The small size of the bulb used in a halogen lamp (and also
    longer life) reduces the economic penalty of using a premium main inert
    fill gas ingredient. Sylvania appears to me to use krypton rather than
    argon as the main inert fill gas ingredient in at least some of their
    "Capsylite" lamps, and their current 100 watt 120V version A19 medium
    screw base version of those is rated to last 3,000 hours and to produce
    1800 lumens. (Sylvania product number 18970, order abbreviation
    100A/HAL/F 120V)
    I remember an older version from the early 1990's claimed to produce
    1880 (give or take) lumens and to last 2250 (give or take) hours - I hope
    I remember correctly! I do remember a different bulb shape - not an "A"
    bulb shape, but with the wider region consisting of two butt-to-butt
    truncated cones.

    - Don Klipstein ()
  16. Phil Allison

    Phil Allison Guest

    "Don Klipstein"

    ** My Q was rhetorical - you fool.
  17. The lumens per watts measures the efficiency of the bulb.

    A typical incandescent is around 15 lumens per watt.

    Differences arise if a halogen cycle is used or if there are temperature
    versus lifetime tradeoffs. Or if shaped "effective lumens" rather than
    real ones are used in sort of an antenna pattern type of thingy.

    The latest of LED's are approaching 150 Lumens per watt.

    A perfect green bulb would be 700 Lumens per watt.
    A perfect white one would be half that.

    Older tutorial at

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  18. Where can I get one? I thought only laboratory prototypes got that
    efficient so far. The most efficient LEDs that I am aware of being in
    production and on the market achieve about 80 lumens/watt.
    683 by definition for 540 THz, approx. 555 nm.
    Depends on what you call white. If the "white light" is equal power per
    unit wavelength from 400 to 700 nm, then light source that is 100%
    efficient at producing such light and nothing outside the 400-700 nm
    range would achieve 243 lumens per watt.

    However, other forms of "white light" can get higher. A perfectly 100%
    efficient light source producing a mixture of 576 nm yellow and 450 nm
    blue to approximate the color of 3500K would achieve 495 lumens per watt.

    - Don Klipstein ()

  19. The LED trade journal is full of high efficiency leds.

    one of our banner advertisers is an industry insider with special
    efficiency expertise ...

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
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