Luminance and Contrast Versus Viewing Direction
Fig. 5 shows luminance and contrast versus viewing direction in a polar coordinate system. The left column shows the directional luminance distribution of the dark state of the display (here: IPS-LCD), the center column shows the bright state and the right column shows the (luminance) contrast (ratio) resulting from the preceding two luminance distributions. The value is coded by (pseudo) colors. The graphs below the polar coordinate systems each show a cross section in the horizontal plane and indicate the values for luminance and for the contrast.
Each borderline between two (shades of) colors represents a line of constant value, in the case of contrast an iso-contrast (contour) line. Note, that "iso" is used here in the sense of "equal", it does NOT establish a relation to the International Organisation for Standardisation, ISO.
This way of representing the variation of a quantity of a display with direction of observation originates from an optical technique called conoscopy. Conoscopy, originally proposed and used by Maugin for examination of the state of liquid crystal alignment in 1911 has been used in every LCD-laboratory in the late seventies and throughout the eighties for measurement and evaluation of the optical properties of LCDs and for estimation of LCD-contrast as a function of viewing direction. In the conoscopic mode of observation, in the old days often realized with a polarizing microscope, a directions image is generated in the rear focal plane of the objective lens. This directions image is based on the same coordinates as the representation in the polar coordinate system shown in figs. 4 and 5.
The first publication of the variation of the contrast of reflective LCDs measured with a motorized mechanically scanning gonioscopic apparatus and represented as a conoscopic directions figure was published in 1979.
Read more about this topic: Viewing Cone
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