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There is a definition of "full spectrum"?

Discussion in 'Lighting' started by Don Klipstein, Oct 28, 2008.

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  1. So far until tonight, I have thought that there was no official
    definition of "full spectrum".

    Now, I had a look at:

    My take is that this is a bit hyped, somewhat along the lines of hype
    that could get worse if there was an "official definition" of "full

    For one thing, that article does appear to me to overemphasize value of
    higher s/p ratio, which I sense has been "fashionable" to do nowadays.
    They say how higher s/p ratio makes a lamp better for outdoor
    illumination (which I think is fairly true), but they talk about s/p ratio
    until they say "Bring Daylight Indoors!"

    I surely like most of my indoor lighting to be "warmer". I have a very
    strong liking to about 3600-3800 K or so, 4100 K when I can practically
    achieve a kilolux or two, and 3400-3500 K looks good to me at 300-500 lux
    or so. At 100-200 lux, 3000-3200 K or so looks good to me!
    At 50-100 lux, I like 2700-2865 K. At 30-50 lux, I like 2700 K. When
    the illumination level needs to be less than 30 lux, I either like
    "utility high-s/p-ratio-daylight" if I want "maximum illumination power
    per watt" at expense of appearing "stark" and "dreary gray", or else I
    like flamelike lower color temp. incandescent (or good high-CRI
    equivalent) with color temp. close to 2500 K. And in a bedroom to enter
    along with a spouse (or girlfriend/boyfriend) while carrying full wine
    glasses and dressed skimpily, probably 1700-2000 K if the color is
    going to approach blackbody.

    One thing they did say:

    "The IESNA Lighting Handbook (3-26) defines full spectrum lighting as
    having spectral emission in all parts of the visible spectrum and in the
    the near UV, with a correlated color temperature of 5000K or more, and a
    CRI of 90 or more."

    Does any edition of the IESNA Lighting Handbook actually define "full
    spectrum" or "full spectrum lighting" as claimed above?

    Why should 7500 K qualify as "full spectrum" while 4800 is "disqualified
    from being full spectrum" when 5400 K is the CCT if "equal energy per unit
    wavelength"? Should not mid-4,000's or maybe even low-4,000's qualify for
    "full spectrum"?

    Does 9300 K or 10,000 K shade of "lighter sky blue" qualify as "full
    spectrum"? Does 20,000 K "deeper sky blue" qualify as "full spectrum"?
    If so, should not a carbon arc at 3800-3900 K qualify as "full spectrum"?

    Any and all comments please!

    - Don Klipstein ()
  2. I would prefer a definition of full spectrum not to be tied
    to any specific colour temperature, but to be that of a
    black body at the same colour temperature (or within some
    permitted deviation). i.e. it's a measure of a full
    spectrum verses discrete spectra, and nothing to do with
    actual colour temperature.
  3. Chris Carlen

    Chris Carlen Guest

    That is a desired consequence of a well designed definition.

    For example, HPX lamps satisfy
    What troubles me about this is that it's too physics oriented. What is
    the context for this definition, light sources for spectrophotometers,
    or light sources for visual illumination?

    If the latter, then I see no reason why a spectrum consisting of
    spectral lines shouldn't be considered as some measure of full spectrum,
    if the lines are spaced closely enough to give high visual rendering
    accuracy (CRI, if you will) for nearly all reflectance spectra of
    practical objects.

    Hence, the requirement #2 that you state above is too demanding, and
    doesn't allow for any continuum between full spectrum or not. Can't we
    devise a definition that gives a number which converges toward some
    value representing 100% continuous spectrum when the test spectrum is in
    fact continuous, and then approaches some other value such as zero when
    a single line spectrum is analyzed?

    To clarify, let's consider a densely populated line spectral
    distribution closely matching the energy vs. wavelength distribution of
    a blackbody. Since no practical visible object is likely to have a
    reflectance spectral distribution that manages to completely miss say,
    all the lines on the red end thereby rendering the color horribly
    distorted, this dense line spectrum of the light source may very well
    render the object as effectively as a black body source of equivalent
    color temp. Thus, why shouldn't this line source be characterized
    somewhere in the range of say 95% full spectrum?

    If however, we were going to use it as a source in a spectrophotometer,
    then we'd have big problems. So in that context, your original
    definition is more suitable, albeit still somewhat problematic since
    what spectral line is actually not differentiable? Every line has a
    finite as opposed to infinitesimal linewidth and thus is differentiable, no?
    Well, it's certainly some good thought as always.

    Good day!


    NOTE, delete texts: "REMOVETHIS" and
    "BOGUS" from email address to reply.
  4. I would counter the disqualification-on-basis-of-differentiality
    ("differentiable" means that "1st derivative exists") on basis that no
    emission "lines"/"bands" have "infinitely steep slopes". If an "emission
    line" has its steepest edges going from 90% of that spectral feature's
    peak to 10% of same in .01 nm or .001 nm or .0001 nm or .000001 nm,
    the spectral power distribution remains a differentiable and continuous
    function of wavelength.

    - Don Klipstein ()
  5. TKM

    TKM Guest

    I checked the 9th edition handbook and actually found the paragraph
    where they take the wording from. From what I can tell, they are
    lifting the statements out of context and using it for their marketing
    purposes. The full paragraph actually reads as follows:

    "While the spectral content of an illuminant might be expected to be
    important for any task where the spectral content changes an important
    aspect of the stimuli the task presents to the visual system, there is
    little evidence that it is important for all tasks. This has not
    stopped claims being made for whatt are called full-spectrum lamps.
    These lamps, which have no widely accepted definition, are typically
    fluorescent lamps with spectral emission in all parts of visible
    spectrum and in the near UV, with a correlated color temperature of
    5000K or more and a CIE General Color Rendering Index of 90 or more.
    Claims have been made that use of such lamps benefit task performance,
    human health, and happiness. These claims have little merit in most

    They (the IES handbook) footnotes the paragraph with a study from the
    National Research Council Canda. 1994. Full-Spectrum lighting
    effects on performance, mood, and healh, edited by Jennifer A. Veitch,
    Insitute for Research in Construction Report no. 659. Ottawa:
    National Research Council Canada.

    You can find the reports at the following link.

    (One of the comment papers in the index was written by Terry McGowan -
    perhaps he can chime in on your question too)

    The NRC report brings back memories -- mainly of the passion surrounding the
    claims made for so-called "full spectrum" lamps. As we've discussed
    numerous times in this forum, however, full spectrum is and remains a
    marketing term and I question whether it deserves anything more

    Since the NRC report was published, we've learned that lamp
    spectrum, by itself, is just one of many factors involving light that might
    have non-visual effects on people. So, maybe we need some sort of
    comprehensive "healthy lighting" index instead with the spectral component
    factored in.

    But, if a technical definition is needed, why not use use the definition
    proposed in the LRC "Lighting Answers"? See:
    The relative cumulative SPD calculation which the LRC calls Full-Spectrum
    Index (FSI) seems to do a good job of capturing the SPD variations and the
    FSI easily answers what I think is the main question: How does lamp "X"
    compare to outdoor daylight, incandescent light or any other sources that
    claims to be full spectrum.

    Terry McGowan
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