Perceived contrast ratio , guest-host

Fig. 6. Computed dependence of perceived contrast ratio on cell thickness for a reflective display with three different guest-host dyes having the indicated dichroic ratios R. Dye concentration adjusted to maintain an on-state brightness of 50%. Concentration of chiral dopant adjusted to maintain 3 turns of the cholesteric helix in the cell.

Fig. 7. Reflected display brightness versus perceived contrast ratio for three guest-host dyes having the indicated dichroic ratios. Increasing the concentration of the dye generally decreases the display brightness and increases the contrast ratio. Values used for this computation ng=1.76, nQ=1.50, d/p 3.0 and d=10.0 ym.

The Perceived Contrast Ratio between on and off states is defined by averaging the transmission with the function of the sensititivity of the human eye y ) and the spectral distribution of the illumination source H ) (4.59). The transmission of the guest-host display is written as... 

The theory developed in the last section can be applied to guest-host displays to obtain results which are of immediate practical interest. In this case the photometric brightness and contrast ratios will be determined because this is what the eye actually perceives. The perceived brightness of the display is given by the integral ... 

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