Open Forum

Metamerism gauges in evaluating K5000/D50 lighting

  • 1.  Metamerism gauges in evaluating K5000/D50 lighting

    Posted 08-29-2018 04:04 PM
    I'm trying to get better lighting in key areas around our shop. In the process I've come across two gauges that supposedly indicate when a light source is correct. But both show different results when under the same source (LED and fluorescent tube), but are the same under daylight.
    The two gauges are the Metamerism gauge produced by Visual Color, marketed for GTI lighting
     metamerism
    The other is the D50 indicator in the back of the Pantone books, similar to the proof stickers they sell here
    Pantone Lighting Indicator Stickers D50

    Does any knowledgeable soul have an educated opinion on which gauge is accurate and should be used?

    Thanks

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    Harold Anderson
    AAA Printing & Graphics
    Bellevue WA
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  • 2.  RE: Metamerism gauges in evaluating K5000/D50 lighting

    Posted 08-30-2018 07:52 AM
    ​I think that your issue is that you are expecting these targets to be gauges.  They are not gauges but indicators - like the lights on your automobile dashboard.  If you do not seem them that is good if your seem them that is bad.  It is the same with the GTI, Pantone and UGRA (Swiss institute for Competence in Printing) D50 test patches.  If you see only 1 color that means you have a good D50 simulation.  If you see two colors then you need to buy different lamps.

    Since metamerism is a spectral based phenomenon, if you did not buy true D50 simulators, then you will see two colors.  This is because to minimize the metamerism between the two patches on the test target, your lamps must have a close match to D50 at all wavelengths.  Typical commercial fluorescent and LED lamps will not meet this criteria and the test strips are not really engineered to report which lamp might be closer to D50.  ISO 3664 describes the requirements and how to test for the quality of a D50 simulator.

    I applaud your work on improving the lighting of your work areas.  Unfortunately, it is not a simple task of just comparing the two colors on a D50 simulator indicator strip.

    ------------------------------
    Danny Rich
    Senior Color Physicist
    Sun Chemical Corporation
    Carlstadt NJ
    (201) 933-4500 x1144
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  • 3.  RE: Metamerism gauges in evaluating K5000/D50 lighting

    Posted 08-30-2018 09:12 AM
    Thank you for the information Dr. Rich but what is confounding me is that these indicators are showing different under the same lights. At our workstations we have Ottlite LCD desk lamps that the Pantone indicator showed as "near perfect" match between the two swatches, then I became aware of the metamerism indicator from Visual Color. That indicator under these same LCD bulbs shows a distinct difference between the two swatches. So, what am I to believe??

    I will now start trying to research ISO 3664 in order to gain some understanding of what's required and specifics about testing for quality. But I'm left wondering why "devices" that are stated to be used for the same outcome arrive at different results.

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    Harold Anderson
    AAA Printing & Graphics
    Bellevue WA
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  • 4.  RE: Metamerism gauges in evaluating K5000/D50 lighting

    Posted 08-30-2018 09:57 AM
    Dear Harold,
     
    Neither metameric pair is capable of verifying compliance to ISO 3664:2009.
      
    The reason you are getting different results from the two color pairs is because they were formulated to appear to match under different light sources (in GTI's case we used our Graphiclite D50 viewing system while in Pantone's case they used a different lighting system - I do not know which).  The light source that is used by the color matcher when formulating these metameric pairs has a significant affect on the appearance of a color match.  In both cases (GTI and Pantone) the two colors are different - they have different spectral reflectance curves thus will have different color appearance in most light sources.  When you create a metameric match - as we did with the card you have - you are trying to make two colors that are not the same appear the same under a specific light source.  Minor changes in the spectral power of the light source will result in a change in the appearance of a color match - thus the difficulty in getting two sets of metameric paris to behave the same when they are matched under different light sources. 
     
     
    The reason those cards exist is to demonstrate the the phenomenom of metamerism.  They are not accurate or precise enough to test and verify that the 5 key elements of the ISO Standard (Light quality, Light intensity, Uniformity of illumination, Geometry of illumination, Neutral gray surround) are being met.  I think that perhaps the capability of the metameric pair has been oversold throughout the years.
     
    The best tool to verify compliance to ISO 3664 is a spectroradiometer that can measure the spectrum of the light falling on your inspection tables.  These can be a bit expensive (in the neighborhood of $5,000).
     
    I have provided a link to a pdf summary of the ISO3664:2009 standard for your review.
     https://www.gtilite.com/wp-content/uploads/2014/03/What-is-the-Viewing-Standard-ISO-3664-2009.pdf

    It is worth the effort to bring your color viewing areas into compliance to the standard ... so keep up the effort.

    Sincerely,

    Bob McCurdy
     
     
    Robert McCurdy
    President
    GTI Graphic Technology, Inc.
    211 Dupont Avenue
    rmccurdy@...
    Tel: 845-562-7066
    Fax: 845-562-2543


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    Robert McCurdy
    GTI Graphic Technology, Inc.
    Newburgh NY
    (845) 562-7066
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  • 5.  RE: Metamerism gauges in evaluating K5000/D50 lighting

    Posted 09-06-2018 10:02 AM
    You could try BableColor CT&A with an i1io2 and get a better idea how close your viewing
    areas are to hitting ISO 3664.  It is not going to be as good as an expensive light meter.
    But if you already have the i1io2, the software isn't too expensive.
    its here BabelColor - Color Measurement and Analysis Software

    ------------------------------
    Bryan Irvine
    Digital Solutions Specialist
    The Advantage Group
    Caledonia MI
    (616) 558-1101
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  • 6.  RE: Metamerism gauges in evaluating K5000/D50 lighting

    Posted 09-10-2018 03:37 PM

    Thank you for replying Robert & Bryan,

    After input here and further research I feel that reaching ISO3664:2009 is a bit above the financial reach of this company at this time, considering it would not only mean investment in lighting, fixtures, software and hardware. I think the best approach for this shop is to choose one of the indicators and use it to achieve "consistent" lighting, thinking "even if it's "wrong" at least it's consistent". Which that will be a giant step considering the various conditions we have presently.

    Robert:
    I am going with the indicator in the back of the Pantone books. My reasons are these:
    "The reason you are getting different results from the two color pairs is because they were formulated to appear to match under different light sources (in GTI's case we used our Graphiclite D50..."
    Knowing that the Metamerism indicator is tested/created for analyzation under GTI lighting, which is priced above the possibilities of this shop currently. I'm hoping the Pantone's indicator might have somehow been more inclusive, or developed under less "controlled" D50 lighting.

    Bryan:
    Thanks! BabelColor's offerings seem affordable and would be valuable to have in this situation.

    Now to balance quality of lighting/color evaluation with the Owner's bottom line.



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    Harold Anderson
    AAA Printing & Graphics
    Bellevue WA
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  • 7.  RE: Metamerism gauges in evaluating K5000/D50 lighting

    Posted 09-11-2018 08:54 AM
    Harold,

    I completely understand the financial concerns you have regarding getting your lighting compliant with ISO3664.  We have done it here, so I know first hand the expense.
    But, may I advise you not to settle for "wrong but consistent lighting".  At the very least, purchase D50 bulbs from GTI for every location you plan on using for color viewing.  Yes, they are more expensive than say a daylight bulb from Home Depot, but they are ISO compliant.  That gets you halfway to compliance assuming the light booths are in proper working order.
    The verification process can be expensive due to the need of a spectroradiometer as someone else mentioned.  But, even if you forego the verification process altogether at this time, using the correct bulbs will pay dividends for you.

    Regards,

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    Patrick Hundley
    Color and Graphic Reproduction Manager
    Hammer Packaging Corporation
    West Henrietta NY
    (585) 350-0150
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