Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1999-04-27
2003-04-29
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S065000, C349S057000
Reexamination Certificate
active
06556258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a display device using ambient light and a lighting panel.
Display devices having a non light-emitting type display element, such as a liquid crystal display element, in which light projected from the outside is used and the transmission of the light is controlled for display, are classified into transmission type display devices using transmitted light and reflection type display devices, using reflected light.
The transmission type display device is a device in which a backlight is arranged at the back of the above-mentioned display element and illuminating light from the backlight is used to perform display. The illuminating light from the backlight is emitted toward the display element and then the light is emitted ahead of the display element to perform the display. In this transmission type display device, a large electric power is consumed to turn on the backlight.
The reflection type display device is a device in which ambient light (outer light), which is light in the use environment of the display device, is used for display. The ambient light incident from the front of the display element is reflected toward the display element on a reflector arranged at the back of the display element and then the light is emitted ahead of the display element to perform the display. In this reflection type display device, reflection light having an intensity according to the outer light incident from the front of the display element can be obtained. Therefore, if the device is in the environment wherein enough outer light is present, display can be observed with sufficient brightness. Any backlight is unnecessary so that a little electric power is consumed.
However, in the reflection type display device, the intensity of the reflected light that is emitted ahead of the display element greatly depends on the intensity of the outer light incident from the front of the display element. Consequently, in the environment of a high illumination over 100000 luxes, for example, in the environment under the direct rays of the sun in summer, the screen is too dazzling so that its display is hard to watch. Moreover, in dark environments, such as the open air at night, such a screen brightness in which display can be recognized cannot be obtained. Thus, the device cannot be used in the dark environments.
On the other hand, hitherto reflection type display devices having an auxiliary,light source have been proposed in order that their display can be observed in dark environments such as the open air at night.
This reflection type display device having an auxiliary light source is a device in which a semi-transmission reflector is arranged at the back of a display element and the auxiliary light source is arranged at the back of the semi-transmission reflector. As the semi-transmission reflector, a reflector having a high reflectivity and a low transmissivity is used in order to ensure a sufficiently high reflectivity of the display device (the ratio of the intensity of emitted light which is reflected on the reflector and emitted ahead of the display element to that of ambient light incident from the front of the display element).
However, in this reflection type display device having the auxiliary light source, the transmissivity of the semi-transmission reflector is very small, and the luminous brightness of the auxiliary light source cannot be made extremely high to make its consumed electric power small. Therefore, when the auxiliary light source is turned on, the brightness of the illuminating light which is transmitted through the semi-transmission reflector and projected into the display element is weak.
For this reason, in the reflection type display device having the auxiliary light source, its screen brightness is low when the auxiliary light source is turned on in dark environments. Furthermore, in the environment of an intense illumination, such as the environment under direct rays of the sun in summer, its screen is too dazzling so that its display is hard to watch.
BRIEF SUMMARY OF THE INVENTION
An object of this invention is to provide a liquid crystal display element making it possible to obtain a display having a suitable screen brightness in various environments from a bright environment to a dark environment.
Another object of this invention is to provide a display device using illuminating light based on ambient light (outer light) and illuminating light based on a turned-on light source to perform display having a suitable screen brightness according to the environmental illumination in the surroundings.
In order to attain the objects, a first aspect of this invention is a display device comprising:
a non light-emitting type display element for controlling the transmission of incident light to display an image,
a light radiating unit arranged at the back of the display element for emitting illuminating light toward the display element and reflecting ambient light incident from the front of the display element at a given reflectivity toward the display element, and
an illumination brightness controller for controlling the intensity of the illuminating light so that the screen brightness of the display element comprising the total of reflected light of the ambient light reflected on the light radiating unit and transmitted light of the illuminating light is set up into a predetermined brightness range according to the reflectivity of the light radiating unit and the environmental illumination of the ambient light incident from the front of the display element.
In such a display device of the first aspect, it is possible to emit both of the reflected light of the ambient light and the transmitted light of the illuminating light ahead from the screen of the display element. At bright environmental illuminations, by adjusting the intensity of the illuminating light in accordance with the illumination of the ambient light, consumed electric power by the environmental illuminating light can be reduced, and the ambient light can be used to obtain a bright screen. At dark environmental illuminations, the screen having a sufficient brightness can be obtained by the reflected light of the ambient light and emission of the transmitted light of the illuminating light from the screen of the display element.
In the display device of the first aspect, the illumination brightness controller controls the screen brightness, according to the environmental illumination, to the brightness corresponding to curves represented by quadratic functions satisfying the following ranges:
a screen brightness of 20-200 nits at an environmental illumination of 50 luxes,
a screen brightness of 30-300 nits at an environmental illumination of 1000 luxes, and
a screen brightness of 400-4000 nits at an environmental illumination of 30000 luxes.
Desirably, the illumination brightness controller controls the screen brightness, according to the environmental illumination, to the brightness corresponding to curves represented by quadratic functions satisfying the following ranges:
a screen brightness of 20-60 nits at an environmental illumination of 50 luxes,
a screen brightness of 60-200 nits at an environmental illumination of 1000 luxes, and
a screen brightness of 1000-3000 nits at an environmental illumination of 30000 luxes.
In the display element wherein its screen brightness is controlled in such a way, even at dark environmental illuminations less than 50 luxes, a screen brightness suitable for observation can be obtained. Even at an environmental illumination of 1000 luxes, which is close to the illumination inside a room, a screen brightness suitable for observation can be obtained. Even at an environmental illumination of 30000 luxes, which is close to the illumination in the open air in the daytime, a screen brightness suitable for observation can be obtained.
In the display device of the first aspect, the illumination brightness controller controls the screen brightness, according to the environmental illumination, to satisfy:
−2×1
Aoki Hisashi
Higuchi Masaru
Muto Tetsuo
Yoshida Tetsushi
Casio Computer Co. Ltd.
Duong Tai
Frishauf Holtz Goodman & Chick P.C.
Kim Robert H.
LandOfFree
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