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Accredited Gemologists Association. Task Force on Lighting and Color-Grading Part I: Lighting And Its Effect on Color-Grading Colorless Diamonds Recap, Standards , Solutions, New Info February 3, 2010. Recap - Task Force Purpose.

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Accredited gemologists association

Accredited Gemologists Association

Task Force on Lighting and

Color-Grading

Part I: Lighting And Its Effect on

Color-Grading Colorless Diamonds

Recap, Standards, Solutions, New Info

February 3, 2010


Recap task force purpose

Recap - Task Force Purpose

~ To develop lighting standards for color grading diamonds to improve reliability and consistency of color grading results, globally ~


Recap task force scope of work

Recap - Task Force Scope of Work

  • Researched global historical teachings and practices

  • Researched established standards by GIA, IDC, CIBJO and PAS

  • Researched science of colorless diamonds including fluorescence

  • Performed scientific testwork of a sample of diamonds in lighting environments commonly used to color grade diamonds.

  • Based on results of testwork, developed standards for an artificial lighting environment which can be repeated globally.

Today – Recap Highlights and Recommend Solutions


The n3 photoluminscence spectra at 80 k

415.2 nm

Energy in

Wavelength (nm)

400375350

Energy in

Electron Volts (eV)

Fluorescence Emission

(Return of excited N3 Center to Ground)

Energy Absorption

(excitation of the N3 Center)

2.998 eV

The N3 Photoluminscence Spectra (at 80°K)

“N3 Photoluminescence Spectrum. Note the almost perfect symmetry of the N3 absorption and luminescence spectra.”

John Walker, Optical Absorption and Luminescence in Diamond

Rep. Prog. Phys., Vol. 42, 1979. Printed in Great Britain

Groupe de Physique des Solides de 1’Ecole Normale SupCrieure


Fluorescence intensity by excitation wavelength

Fluorescence Intensity by Excitation Wavelength

Sample of one 3.02ct VST Blue Fluorescent Diamond

Contributed by Thomas Hainshwang, DUG, FGA, GG, Experte SGG


Fluorescence intensity by excitation wavelength1

Fluorescence Intensity by Excitation Wavelength

Sample of one 3.02ct VST Blue Fluorescent Diamond

Data contributed by Thomas Hainshwang, DUG, FGA, GG, Experte SGG


Accredited gemologists association

Spectral Transmittance of Tavernier Diamond with and without Blue Fluorescence /Blue Fluorescence Intensity caused by UV from D65 Daylight Simulator

“A few colorless to light yellow diamonds have very strong fluorescence, which can change their appearance with light sources with and without a UV component” [15% of all blue fluorescent diamonds are ST or VST]

“The blue fluorescence can make a light yellow diamond appear less saturated (more colorless)”.

Color research and application, Volume 23, Number 5, Oct 1998

Contributed by: Martin Haske, GG (GIA), BS/MS (MIT)


Color grading a 25 sample diamond set in six separate grading environments

Color Grading a 25 Sample Diamond Set in Six Separate Grading Environments

Test Results

  • VST Blue – Up to 4.5 grade improvement from UV + Visible Violet,

    • with VV contributing 1 to 2 grade improvement

  • ST Blue – 2 grade improvement

  • MED Blue – 1 grade improvement

  • Faint/None Blue – No perceptable differences

  • Contributed by Michael Cowing, FGA, M.Sc


    Changes in distance understanding variation in unfiltered uv energy

    Changes in Distance - Understanding Variation in (unfiltered) UV Energy

    Degree of perceived color improvement over the true body color (color absent fluorescence) is proportional to both the diamond’s fluorescent strength and the strength of the [unfiltered] UV energy from the grading light source.

    Contributed Michael Cowing, FGA, M.Sc.


    Understanding cie indoor daylight illuminant d65

    Understanding CIE Indoor Daylight Illuminant D65

    • “Developed for industrial [textile] applications needing indoor daylight spectra for average colormetric work”

    • “Considers transmission of clear glass samples only”

    • “In practice, glass coatings become more important and must be considered by CIE in future”

    • “In future, CIE hopes to be able to recommend indoor daylight sources”

    • Appendix A – “Special glazing systems are capable of reducing energy consumption for heating in winter and cooling in summer, reducing glare from outside and minimizing UV fading of furnishings.

    Data from International Commission on Illumination (CIE); Indoor Daylight Illuminant D65


    Xenon daylight simulator cie illuminant d65

    Xenon Daylight Simulator – CIE Illuminant D65

    Color research and application, Volume 23, Number 5, Oct 1998

    Contributed by: Martin Haske, GG (GIA), BS/MS (MIT)


    White or uv fluorescent light bulb how it works

    White or UV Fluorescent Light Bulb – How It Works

    University of Technology, Applied Physics

    Eindhoven, Netherlands

    Leon Bakker


    Spectral power distribution and uv intensity 3 lighting technologies fluorescent incandescent led

    Spectral Power Distribution and UV Intensity3 Lighting Technologies – Fluorescent, Incandescent, LED

    Each measurement

    at 300fc


    Spectral power distribution and uv intensity 3 lighting technologies critical emission wavelengths

    Polycarbonate UV Filter (Lexan or Macrolon)

    Blocks all energy < 390nm

    Spectral Power Distribution and UV Intensity3 Lighting Technologies – Critical Emission Wavelengths

    “Visible Violet” N3

    Excitation Wavelengths


    Accredited gemologists association

    Lighting Standards for Color Grading Colorless Diamonds

    AGA Task Force on Lighting and Color Grading Colorless Diamonds

    AGA Conference, Tucson, AZ


    Accredited gemologists association

    Solutions for Lighting Standards Compliance

    Purchase 2 simple, commercially available meters to monitor and document your grading environment: 1) light meter, and 2) UV radiometer.

    Change your fluorescent bulbs once a year. Note manufacturer, model number.

    Before you use the fluorescent bulbs, burn them in for 160hrs to achieve color stability (leave on for 7 days).

    Buy a piece of lexan or makrolon polycarbonate and affix it to your grading equipment in order to filter UV energy emitted from the bulbs. If you choose to report both perceived color and true body color, make sure the filter can be readily removed.

    After bulb burn in, take and record UV energy and light intensity measurements at the distance you grade from the light source. Avoid varying this distance when making final color grade decisions.

    Independent certification of your grading environment by a qualified independent testing lab is suggested for gemologists involved with litigation.

    AGA Task Force on Lighting and Color Grading Colorless Diamonds

    AGA Conference, Tucson, AZ


    New info uv fluorescent bulbs

    New Info - UV Fluorescent Bulbs

    • UV fluorescent bulbs are not all created equally, just like white fluorescent bulbs

    • Function similar to white fluorescent bulbs but different phosphors and coatings to control energy emitted

    • Black Light bulb (BL) vs Black Light Blue (BLB)

    • Use Wood’s Glass=nickel-oxide-doped glass also known as Hoya U-325glass to block visible light above 400nm (VIS)

    • Long Wave UV Bulbs peak at 365nm

    • Short Wave UV Bulbs peak at 254nm


    New info short wave uv bulb 254nm

    New Info – Short Wave UV Bulb (254nm)


    New info long wave uv 365nm bl vs blb bulbs

    New Info – Long Wave UV (365nm) – BL vs BLB bulbs

    Black Light Blue bulb

    • BLB has a thin coating of a visible wavelength (VIS) filter generally applied to the inner wall of the bulb.

    • Color of the bulb appears “blacklight blue” or “BLB”.

      Black Light bulb

    • BL does not include the VIS filter coating. Visible spectrum observable when powered on.

    • Wood’s glass is used as a bandpass filter used in combination with a BL bulb. Expensive.

      Important Points

    • Different manufacturers use different phosphors, glass, and coatings for different purposes. Know your bulb !!!

    • The BL and BLB bulbs are not interchangeable without impacting your fluorescence grading.


    New info 6w long wave uv bulbs 365nm

    New Info – 6W Long Wave UV Bulbs (365nm)


    New info 6w long wave uv bulbs 365nm1

    New Info – 6W Long Wave UV Bulbs (365nm)


    New info 4w long wave uv bulbs 365nm

    New Info – 4W Long Wave UV Bulbs (365nm)


    Don t stress

    Don’t Stress !!!

    CERTIFY YOUR GRADING BOX!


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