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Conquering Electronic Display Reflection Measurement Irreproducibility

2. Need for Good Display Metrology. Level Playing Field

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Conquering Electronic Display Reflection Measurement Irreproducibility

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    1. Conquering Electronic Display Reflection Measurement Irreproducibility Kent State University Seminar April 11, 2001

    2. 2 Need for Good Display Metrology

    3. 3 Illuminance Meter — Cosine Corrected? For small source at q, illuminance goes as cosq. If illuminance meter is cosine corrected, E/cosq should be constant. Should know if it is not. Devices & Deployment

    4. 4 Luminance & Illuminance Meter Comparison Devices & Deployment, Cont.

    5. 5 Reflectance Factor, R: Ratio of the reflected flux from the material within a specified cone to the flux that would be reflected from a perfect (reflecting) diffuser (perfectly white Lambertian surface) under the same specified illumination: Special cases: Canonical Reflection Terminology

    6. 6 Reflectance, Diffuse Reflectance r : Ratio of the (entire, W = 2p) reflected flux to the incident flux: Luminance Factor b : Ratio of the luminance of the object to that of the luminance of a perfect reflecting diffuser (perfectly white Lambertian materiel) for identical illumination conditions:

    7. 7 Helmholtz Reciprocity “Law”: bd/q = rq/d

    8. 8 Oversimplified Models — Possible Ambiguity “Diffuse” (Lambertian) component assumption: Display surface measured as if it were matte paint. b = luminance factor, q = luminous coefficient, E = illuminance, L = observed luminance. Strictly speaking this equation is for a Lambertian material: “diffuse” means scattered out of specular direction and is not limited to Lambertian materials. Specular component assumption: Display surface treated as if it were a mirror. rs = specular reflectance, Ls = source luminance Reflection Measurements

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    10. 10 Specular, Lambertian (Matte or “Diffuse”), Haze Most think in terms of specular (mirror like) and diffuse (Lambertian-like) and lump haze in with either or both. Here we are separating out the three.

    11. 11 Specular, Lambertian, Haze

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    13. 13 Reflection Measurements, Cont.

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    15. 15 Reflection Measurements, Cont. Like the Lambertian component, the haze is proportional to the illuminance; but like the specular component, it follows the specular direction.

    16. 16 Reflection Measurements, Cont. Reflection of laser beam onto white card gives the BRDF projected onto a plane.

    17. 17 Reflection Measurements, Cont. Three components in BRDF often seen in CRTs

    18. 18 Reflection Measurements, Cont.

    19. 19 Reflection Measurements, Cont. Haze exhibits angular sensitivity to position of source. What contrast do we want???

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    21. 21 Reflection Measurements, Cont.

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    34. 34 White Reflectance Standard Possible to obtain types that can be refurbished in your lab (e.g., 220 to 240 grit water-proof emery paper using circular-linear combined motion under running water). Make sure it is sufficiently thick (some need to be 10 mm depth or more, whatever the manufacturer states is necessary). A 50 mm diameter disk may be required. Over 99% reflectance (e.g. r0/d ), quasi-Lambertian… BUT watch out!!! … What kind of reflectance is this 99% value???

    35. 35 Luminance Factor of White Standard Example Examples ONLY; don’t use these results for your own purposes!!! This shows that you cannot plop one of these in your apparatus, measure its luminance, assume a luminance factor of 0.99 and calculate the illuminance—it just isn’t that simple.

    36. 36 Luminance Factor of White Standard Example, Cont. Example ONLY; don’t use these results for your own purposes!!! Specular configuration bq/q has very different characteristics from bq/0 configuration.

    37. 37 Luminance Factor of White Standard Example, Cont. Example ONLY; don’t use these results for your own purposes!!! Source at normal b0/q

    38. 38 Luminance Factor of White Standard Example, Cont. Example ONLY; don’t use these results for your own purposes!!! Diffuse illumination bd/q

    39. 39 Luminance Factor of White Standard Example, Cont.

    40. 40 Black glass Useful for making measurements of source in specular reflection configuration. Note slight angle dependence of specular reflectance.

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