Liquid crystal display device

1. A liquid crystal display device comprising:

a backlight; and

a pixel portion including:

a first region comprising a first pixel and a second pixel;

a second region comprising a third pixel and a fourth pixel; and

a third region comprising a fifth pixel,

wherein the second pixel is located closer to the second region than the first pixel,

wherein the third pixel is located closer to the first region than the fourth pixel,

wherein each of the first pixel, the second pixel, the third pixel, the fourth pixel and the fifth pixel includes a liquid crystal element and a transistor being configured for controlling holding of a voltage supplied to the liquid crystal element,

wherein the backlight includes first light sources configured to emit a first hue, second light sources configured to emit a second hue, and third light sources configured to emit a third hue,

wherein each of the first region and the second region comprises a plurality of pixels each including a transparent pixel electrode and a reflective pixel electrode,

wherein, in a first case of expressing a color image in a frame period, one of the first light sources lights the first pixel in a first period, one of the second light sources lights the first pixel in a second period, one of the third light sources lights the first pixel in a third period, another one of the first light sources lights the second pixel in a fourth period, another one of the third light sources lights the third pixel in the first period, another one of the first light sources lights the third pixel in the second period, another one of the second light sources lights the third pixel in the third period, another one of the third light sources lights the fourth pixel in the fourth period, and another one of the second light sources lights the fifth pixel in the first period,

wherein the first period and the fourth period only partially overlap with each other,

wherein the second period and the fourth period only partially overlap with each other,

wherein the first period, the second period, and the third period do not overlap with each other,

wherein, in a second case of expressing a monochrome image, the first pixel, the second pixel, the third pixel and the fourth pixel are configured to express the monochrome image by external light reflected by the reflective pixel electrodes,

wherein, in the second case, none of the first light sources, the second light sources, and the third light sources emit light, and

wherein a period for the holding of a voltage is 10 seconds or more.

2. The liquid crystal display device according to claim 1 , wherein a channel formation region of the transistor includes an oxide semiconductor.

3. The liquid crystal display device according to claim 2 , wherein the oxide semiconductor is an In—Ga—Zn—O-based oxide semiconductor.

4. The liquid crystal display device according to claim 2 , wherein a hydrogen concentration of the oxide semiconductor is less than or equal to 5×10 19 /cm 3 .

5. The liquid crystal display device according to claim 1 ,

wherein the number of writings of first image signals to the pixel portion in a frame period is lower than that of second image signals to the pixel portion in the frame period,

wherein the first image signals are input for expressing the monochrome image, and

wherein the second image signals are input for expressing the color image.

6. A liquid crystal display device comprising;

a backlight;

a pixel portion including:

a first region comprising a first pixel and a second pixel;

a second region comprising a third pixel and a fourth pixel; and

a third region comprising a fifth pixel; and

a photometric circuit configured to measure a peripheral brightness,

wherein the second pixel is located closer to the second region than the first pixel,

wherein the third pixel is located closer to the first region than the fourth pixel,

wherein each of the first pixel, the second pixel, the third pixel, the fourth pixel and the fifth pixel includes a liquid crystal element and a transistor being configured for controlling holding of a voltage supplied to the liquid crystal element,

wherein the backlight includes first light sources configured to emit a first hue, second light sources configured to emit a second hue, and third light sources configured to emit a third hue,

wherein each of the first region and the second region comprises a plurality of pixels each including a transparent pixel electrode and a reflective pixel electrode,

wherein, in a first case of expressing a color image in a frame period, one of the first light sources lights the first pixel in a first period, one of the second light sources lights the first pixel in a second period, one of the third light sources lights the first pixel in a third period, another one of the first light sources lights the second pixel in a fourth period, another one of the third light sources lights the third pixel in the first period, another one of the first light sources lights the third pixel in the second period, another one of the second light sources lights the third pixel in the third period, another one of the third light sources lights the fourth pixel in the fourth period, and another one of the second light sources lights the fifth pixel in the first period,

wherein the first period and the fourth period only partially overlap with each other,

wherein the second period and the fourth period only partially overlap with each other,

wherein the first period, the second period, and the third period do not overlap with each other,

wherein, in a second case of expressing a monochrome image, the first pixel, the second pixel, the third pixel and the fourth pixel are configured to express the monochrome image by external light reflected by the reflective pixel electrodes,

wherein, in the second case, the first light sources, the second light sources, and the third light sources are configured to emit lights in accordance with the measurement results of the photometric circuit, and

wherein a period for the holding of a voltage is 10 seconds or more.

7. The liquid crystal display device according to claim 6 , wherein a channel formation region of the transistor includes an oxide semiconductor.

8. The liquid crystal display device according to claim 7 , wherein the oxide semiconductor is an In—Ga—Zn—O-based oxide semiconductor.

9. The liquid crystal display device according to claim 7 , wherein a hydrogen concentration of the oxide semiconductor is less than or equal to 5×10 19 /cm 3 .

10. The liquid crystal display device according to claim 6 ,

wherein the number of writings of first image signals to the pixel portion in a frame period is lower than that of second image signals to the pixel portion in the frame period,

wherein the first image signals are input for expressing the monochrome image, and

wherein the second image signals are input for expressing the color image.

11. The liquid crystal display device according to claim 4 , wherein an off-state current density of the transistor is less than or equal to 100 yA/μm.

12. The liquid crystal display device according to claim 9 , wherein an off-state current density of the transistor is less than or equal to 100 yA/μm.

13. An electronic device comprising the liquid crystal display device according to claim 1 .

14. An electronic device comprising the liquid crystal display device according to claim 6 .

15. The liquid crystal display device according to claim 1 ,

wherein, in the first case of expressing the color image in the frame period, another one of the second light sources lights the second pixel in a fifth period, another one of the first light sources lights the fourth pixel in the fifth period,

wherein the second period and the fifth period only partially overlap with each other, and

wherein the third period and the fifth period only partially overlap with each other.

16. The liquid crystal display device according to claim 6 ,

wherein, in the first case of expressing the color image in the frame period, another one of the second light sources lights the second pixel in a fifth period, another one of the first light sources lights the fourth pixel in the fifth period,

wherein the second period and the fifth period only partially overlap with each other, and

wherein the third period and the fifth period only partially overlap with each other.