Fig.l Schematic diagram of a VHC cell.

ABSTRACT A very high contrast liquid crystal display ( VHC ) was developed. The VHC is based on 3 technologies; light shielding black mask, the positive mode twisted nematic configura­ tion and an inversed driving method.Maximum contrast ratio exceeds 1,000, and thus it realizes a "bleed-through" free dash­ board display. The VHC has some additional advantages, such as little temperature depend­ ence in ON-color, fast switching speed and so on.Typical usages of the VHC in the instrument panels are described. 1. The twisted nematic liquid crystal display (TN-LCD) has been used in automotive appli­ cations. The negative mode TN-LCD is a typical usage for instrument panels ,considering various conditions of ambient brightness. However, it has been one of the most important problems to minimize the background transmission ("bleed-through"), since the bleed- through is an inevitable property of the negative mode TN cell.The background transmission (Toff) is expressed by the Gooch-Tarry equation for perpen­ dicularly incident light. !Toff = sin2 (7rv"l + u2 )/ (1+u2 ) (1)here u = 2And/^ , Andoptical anisotropy of liquid crystalcell gapwavelengthIf the following condition is satisfied, the background becomes completely dark,/1+u2 = 2 N ( N = 1, 2, 3, - ) (2)However, the optimum condition is not always satisfied for the whole temperature range because of temperature dependence of And.The addition of dichroic dye into the liquid crystal material2 or the modulated TN ( MTN ) :i can be solutions for the bleed-through problem. However, contrast ratio is about 100 at most, and some transmission through the background has to be considered in design­ ing a dashboard display.The VHC was developed to realize bleed-through free displays.