Front lighting system for liquid crystal display

#The invention relates generally to liquid crystal displays (LCDs) and particularly to a front lighting system for a liquid crystal display.

#Liquid crystal displays (LCDs) are used in portable computers and other electronic devices to display information. LCDs modulate light to create images using selectively transmissive and opaque portions of the display, the selection being controlled by passing electric current through the liquid crystal material. LCDs are available in transmissive, reflective and transflective versions. A transmissive LCD is illuminated by an artificial backlight positioned behind the LCD glass to provide the contrast between the light transmissive and opaque portions of the display. The transmissive LCD can be adequately viewed only when the backlight is illuminated. When the backlight is illuminated, this type of LCD is very readable in low to medium light, with a typical contrast ratio of 18:1 for the very best LCDs. Under strong lighting conditions, however, the contrast ratio is significantly lower, making the LCD more difficult to read. Another drawback to transmissive LCDs is that the backlight consumes a significant amount of power making them somewhat undesirable for use with portable devices, in which power conservation is a concern.

#A reflective LCD has a rear reflective surface and is illuminated from the front of the display, typically by ambient light similar to LCD watches, to provide the contrast necessary for readability. Reflective LCDs provide a fairly high contrast in medium to strong light, but are difficult, if not impossible to read in low or nonexistent light. On the positive side, however, because a backlight is not used, reflective LCDs consume considerably less power than their transmissive counterparts.

#FIG. 1 is a perspective view of a portable computer with a liquid crystal display front-lighting system incorporating features of the present invention;

#FIGS. 2A and 2B are enlarged, cross-sectional views of the front lighting system taken along line 2--2 of FIG. 1 showing alternate positions of the retractable light source;

#FIG. 3 is a schematic view taken along line 3--3 of FIG. 1;

#In FIG. 1, the reference numeral 10 designates a portable computer system incorporating the features of the present invention. The system 10 includes a base 12 and a display system 14. The display system 14 includes a lid 16, a reflective LCD 18, and light sources 20.

#As best shown in FIGS. 2A and 2B, each light source 20 includes a switch 22, a fluorescent tube or bulb 24A and 24B, and a housing 26 having a cover 28 and a lens 30. The bulb is secured within the housing 26, and the housing 26 is pivotally connected to the display housing 16 by a spring hinge 32. The housing 26 is rotatable between a closed position (FIG. 2A) and an open position (FIG. 2B), with the spring hinge 32 urging the housing 26 toward the open position. In the closed position, the housing 26 contacts the switch 22 to keep the bulb 24A or 24B turned off, and in the open position the housing 26 is removed from contact with the switch 22 to turn the bulb 24A or 24B on. A spring loaded latch 34 is disposed in the lid 16, so that the spring 36 urges the latch 34 toward the housing 26. When the housing 26 is in the closed position (FIG. 2A), the latch 34 mates with a notch 38 in the housing 26 to retain the housing 26 in the closed position. The latch 34 may be manually moved away from the housing 26 so that the latch 34 clears the notch 38, permitting the spring hinge 32 to move the housing 26 to the open position.

#As shown in FIG. 3, a grazing incidence reflecting film 40 made of a transparent polymer is applied to the front surface of the LCD 18. The film 40 has a microreplicated surface designed to increase optical transmission at glancing angles and to direct the light toward the LCD 18. The micro replicated surface is designed to provide a plurality of transparent, multifaceted microstructures 42 which are disposed along the front surface of the film 40 for directing light toward the LCD 18 and collimating the light as the light passes through the film 40 toward the LCD, as will be described.