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Some s/p ratio figures that I question

Discussion in 'Lighting' started by Don Klipstein, Feb 16, 2010.

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  1. I am aware of how s/p ratio is hyped. I seem to think it's
    often overhyped, but that is only my opinion based on my experience of my
    sensation of illumination achievement as a function of my light meter
    reading and s/p ratio.

    However, there is also the matter of some bad figures being published.
    When web-searching for s/p ratios of various light sources, I find many
    hits to be from those selling a particular lamp technology or two. In
    some of those cases, some of the figures for lamps of types they are
    competing against appear to me to be low.

    Then there are widely-repeated figures by Sam Berman, which I
    best-found so far in a 1995 paper of his
    (http://gaia.lbl.gov/btech/papers/42327.pdf),
    and his work there for the s/p ratio figures of various lamps appears
    to me to be in a 1992 paper of his
    (http://gaia.lbl.gov/btech/papers/30844.pdf).

    The one for "clear mercury" (.8) caught my attention as very unusual
    for its usual correlated color temperature. Also, my visual experience
    outdoors at night (where s/p ratio counts more due to lower illumination
    levels) suggested that .8 "sounds low".

    So, I wanted to try my own hand at it comong up with a determination or
    "determination" of s/p ratio of "clear mercury".

    I think I know spectral power distribution of a 175 watt clear mercury
    lamp well enough to do that at least fairly well. I come up with 1.26.

    With more web searching, I find that the Lighting Research Center at
    Rensellaer Polytechnic Institute somehow/somewhere came up with 1.33 for
    s/p ratio of 400 watt "clear mercury":

    http://www.lrc.rpi.edu/programs/solidstate/pdf/euroLED2008.pdf

    I did check many of Berman's other figures, and found them quite
    true, although LRC at RPI appears to me to confirm Berman's figure for
    an Na-Sc metal halide lamp best in the case of a phosphor-coated one
    more than in the case of clear ones (which LRC shows slightly higher).

    It appears to me that Berman achieved at least reasonably good
    determinations, with the exception of one lamp being subject to a
    computer mishandling something or something along those lines.

    However, when I web-searched for s/p ratio of mercury vapor lamps,
    mercury lamps, "clear mercury", etc. I ran into .8 dozens of times
    and 1.33 once.

    (Those selling lamps other than mercury vapor on basis of s/p ratio
    appear to me likely to have a motive to report .8 rather than 1.33
    for mercury vapor.)

    I have decided to publish s/p ratios of various light sources, ones
    that I "best-determined" to be true, whether calculation of knowable
    or measured spectral power distibution or cited by a "reasonably
    authoratative source" and "ringing true to me". And with citation to
    where they came from.

    http://members.misty.com/don/spratio.html

    A few of these are original work of mine, based on spectral power
    distributions obtained by a friend of mine with a spectrometer. 3 of
    the figures there from my original workings are for 2 different red
    LEDs plus 1 of those with either of two spectrally-similar specific red
    filters, trying for extreme low s/p ratio from practical light sources.

    Any comments?
     
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