Image sticking measurement method for liquid crystal display device

• US 20020067325A1
• Filed: 10/17/2001
• Published: 06/06/2002
• Est. Priority Date: 10/19/2000
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Philips LCD Company Limited (LG Display Co., Ltd.)
• Inventors: Choi, Hyoung Rack
• Granted Patent: US 6,791,520 B2
• Time in Patent Office: Days
• US Class Current: 345/89
• CPC Class Codes: G09G 2320/0257 Reduction of after-image effects
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A method for measuring an image-sticking defect in a liquid crystal display device includes steps of irradiating light from a backlight to the liquid crystal display device, displaying a first full white state on a liquid crystal display screen of the liquid crystal display device to which the light is irradiated, measuring first luminance values of a plurality of designated points on the liquid crystal display screen, calculating an average luminance value of the first full white state using the first luminance values, displaying a full black state on the liquid crystal display screen, measuring second luminance values of the plurality of designated points on the liquid crystal display screen, calculating an average luminance value of the full black state using the second luminance values, forming a gray scale using the average luminance value of the first full white states and the average luminance value of the full black state, displaying a second full white state on the liquid crystal display screen, and measuring a luminance change of the second full white state with time at the plurality of designated points using the gray scale.

Claims

1. A method for measuring an image-sticking defect in a liquid crystal display device, comprising:

irradiating light from a backlight to the liquid crystal display device;

displaying a first full white state on a liquid crystal display screen of the liquid crystal display device to which the light is irradiated;

measuring first luminance values of a plurality of designated points on the liquid crystal display screen;

calculating an average luminance value of the first full white state using the first luminance values;

displaying a full black state on the liquid crystal display screen;

measuring second luminance values of the plurality of designated points on the liquid crystal display screen;

calculating an average luminance value of the fall black state using the second luminance values;

forming a gray scale using the average luminance value of the first full white state and the average luminance value of the full black state;

displaying a second full white state on the liquid crystal display screen; and

measuring a luminance change of the second full white state with time at the plurality of designated points using the gray scale.

2. The method according to claim 1, wherein a number of the plurality of designated points is 13.

3. The method according to claim 1, further comprising:

measuring a luminance value of the backlight while displaying the first full white state on the liquid crystal display;

measuring a luminance value of the backlight while displaying the full black state on the liquid crystal display; and

obtaining an inherent luminance value of the backlight.

4. The method according to claim 3, wherein the step of obtaining an inherent luminance value of the backlight includes comparing the luminance value of the backlight of the first full white state to the luminance value of the backlight of the full black state.

5. The method according to claim 4, further comprising:

calculating a transmission percentage ratio of the average luminance value of the first full white state to the inherent luminance value of the backlight.

6. The method of claim 5, further comprising:

obtaining a luminance change percentage ratio by calculating a ratio of a brightest luminance value to a darkest luminance value of the second full white state at the plurality of designated points; and

measuring the image-sticking defect using a difference between the transmission and the luminance change percentrage ratio.

7. The method according to claim 1, wherein a voltage applied to the liquid crystal display device during the step of displaying a first full white state is equal to a voltage applied to the liquid crystal display device during the step of displaying a second full white state.

8. A method for quantifying an image-sticking defect of a liquid crystal display device, comprising:

displaying a first full white state on a liquid crystal display screen of the liquid crystal display device via a backlight source;

calculating an average luminance value of the first full white state using luminance measurement values of a plurality of designated points on the liquid crystal display screen;

measuring a first luminance value of the backlight source;

displaying a full black state on the liquid crystal display screen;

calculating an average luminance value of the full black state using luminance measurement values of the plurality of designated points on the liquid crystal display screen;

measuring a second luminance of the backlight source;

generating a gray scale with the average luminance values of the first full white and full black states, the gray scale having 64 levels;

displaying a second full white state on the liquid crystal display screen;

measuring a brightest luminance value and a darkest luminance value;

calculating a luminance change ratio using the brightest luminance value and the darkest luminance value;

calculating a transmission ratio using the average luminance value of the first full white state and the first luminance value of the backlight source; and

quantifying the image-sticking defect using the luminance change ratio and the transmission ratio.

9. The method according to claim 8, wherein the step of displaying a first full white state occurs for a first time period of at least about 30 minutes.

10. The method according to claim 9, wherein the first time period is approximately 2 hours.

11. The method according to claim 8, wherein a number of the plurality of designated points is 13.

12. The method according to claim 8, wherein the step of displaying a full black state occurs for a second time period of about two hours.

13. The method according to claim 8, wherein the luminance change ratio is calculated using the following expression:

14. The method according to claim 8, wherein the transmission ratio is calculated using the follow equation:

16. The method according to claim 15, wherein the gray scale includes 64 levels.

17. The method according to claim 16, wherein a 0-level of the gray scale corresponds to the full black state and a 63rd-level corresponds to the full white state.

15. A method for generating a gray scale of a liquid crystal display device, comprising:

displaying a full white state on a liquid crystal display screen of the liquid crystal display device;

calculating an average luminance value of the full white state using luminance measurement values of a plurality of designated points on the liquid crystal display screen;

displaying a full black state on the liquid crystal display screen;

calculating an average luminance value of the full black state using luminance measurement values of the plurality of designated points on the liquid crystal display screen; and

generating a gray scale with the average luminance values of the full white and black states.

18. A method for measuring a luminance change ratio of a liquid crystal display device, comprising:

displaying a first full white state on a liquid crystal display screen of the liquid crystal display device;

calculating an average luminance value of the full white state;

displaying a full black state on the liquid crystal display screen;

calculating an average luminance value of the full black state;

generating a gray scale with the average luminance values of the full white and black states;

displaying a second full white state on the liquid crystal display screen;

measuring brightest and darkest luminance values; and

calculating the luminance change ratio using the brightest and darkest luminance values.