Microfading Tester International Discussion Group

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  • 1.  Xe lamp and water filter for Whitmore MFT?

    Posted 05-28-2026 11:46

    I have a few questions regarding the standard Whitmore design MFT system that we have at Winterthur.

    1) What type of Xe lamp have people selected for MFT using the Whitmore design: standard or ozone free? The latter generates less UV, but unless one is interested in UV induced fading or optical brighteners visible light (400-700 nm) should suffice.

    2) Has anyone used a 100 W Xe arc lamp instead of the 75 W lamp that seems to be the standard choice?

    3) Our Whitmore MFT system at Winterthur also has a water filter installed on the Xe arc lamp housing, but the filter is empty and infrared radiation is instead removed by a glass optical filter. Have MFT users with similar systems removed the water filters since they are no longer needed (and generally require some type of temperature stabilized water circulation to use)?  

    Thanks in advance for any advice you can share!

    Best regards,

    Mike Crawford



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    Michael Crawford
    SRAL Volunteer
    Winterthur Museum, Garden & Library
    Glen Mills
    United States
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  • 2.  RE: Xe lamp and water filter for Whitmore MFT?

    Posted 06-05-2026 11:36
    Hi Mike,
    We had the standard xenon-arc lamp (#6251NS, Newport), but we've recently changed to the ozone-free xenon-arc lamp (#6263, Newport). The reason we changed to the ozone-free lamp is occupant health, as it reduces ozone generation from UV below 260nm. Above 260nm, the irradiance of the #6251NS and #6263 lamps appears similar, so we apply a UV filter and a hot mirror to block UV.
    Regarding power, we use 75W lamps. We operate our Whitmore system at around ~800 mlm, and 75W was enough to reach the light level. Also, we feel like we don't need to expose our samples to a higher light dose. However, when a light bulb deteriorates, we increase our wattage slightly higher with a digital controller. 
    Our Whitmore system also has a water filter; however, we don't use it due to the complication of connecting to the DI water. We spoke to Newport, and they suggested removing it if we don't use it, since it can reduce the light output. We use a hot mirror to cut the IR, and it seems sufficient.
    I hope my answers are helpful, and I am happy to discuss more if you have any follow-up questions.


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    Jenny Kim
    Assistant Scientist
    Getty Conservation Institute
    Los Angeles
    United States
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  • 3.  RE: Xe lamp and water filter for Whitmore MFT?

    Posted 06-06-2026 21:55
    Hi Jenny,
    Thank you very much for your answers to my questions, they are very helpful.
    We also are considering the ozone free Xe-arc lamp to eliminate the need for an elephant trunk over the lamp to remove ozone. 
    A few more questions:
    1) How does Blue Wool fading behavior compare using standard vs ozone free Xe-arc lamps? 
    2) Based on Newport's recommendation, did you remove the water filter? If you did remove it, by how much did the luminous flux increase?
    3) How do you measure the focal spot diameter for your MFT system? What is a typical diameter?
    4) As the Xe-arc lamp ages, does the MFT data become noisier? Based on your experience, how long does a Xe-arc lamp last? Approximately 400 hours, the lifetime given by Newport?
    Thanks again for your help!
    Best regards,
    MIke



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  • 4.  RE: Xe lamp and water filter for Whitmore MFT?

    Posted 19 days ago
    Dear Mike

    On question (3) How do you measure the focal spot diameter for your MFT system? What is a typical diameter?

    There are a number of ways of measuring spot diameter. For a handy survey see Swit et al, 'Beam characterization of a microfading tester: evaluation of several methods', Heritage Science (2021) 9:78 (https://doi.org/10.1186/s40494-021-00556-7). 

    I generally use a camera method - focus the spot at very low intensity on a bare webcam CCD with known pixel dimensions. The trick here is getting the spot intensity low enough that the 8-bit dynamic range of the webcam CCD sensor is not saturated. With Whitmore systems this usually requires an ND2 and an ND3 filter stacked after your hot mirror. This will (typically) give you a max value on your CCD of <250. 

    The motivation for ensuring that your sensor is not saturated is to determine whether the beam profile is flat-topped or Gaussian (xenon sources tend to be more Gaussian, LED sources tend to be more flat-topped).

    Once you have a picture of your spot that is not saturated, and you know the  pixel dimensions of the CCD sensor, you can use ImageJ (or Fiji) to draw profile lines through your spot get the spot profile, and then take an appropriate measure of the spot diameter (quite often, people use the full width half maximum). 

    I will typically focus and take an image, calculate the FWHM, and repeat this  process five times to get an average, and determine the standard deviation of the sample to ensure that we're converging on a single value. 

    It is possible to buy camera beam profilers if you don't want to take a webcam apart for a bare CCD.  However, these are quite expensive. 

    You can sanity check your result with a photo-active paper (Vincent can probably sepak more to this).

    Happy to talk more about this if you have questions...

    JP

    JP Brown (he/his)
    Senior Conservator
    Vice-Chair MFT-IDG

    Field Museum
    1400 S. DuSable Lake Shore Dr.
    Chicago, IL 60605



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