Electrophoretic device with ambient light sensor and adaptive whiteness restoring and color balancing frontlight

Patent metadata

Field	Value
Publication number	US-12412538-B2
Application number	US-202418731572-A
Country	US
Kind code	B2
Filing date	Jun 3, 2024
Priority date	Jun 27, 2023
Publication date	Sep 9, 2025
Grant date	Sep 9, 2025

Abstract

An electrophoretic display apparatus includes an ambient light sensor and a frontlight system for adaptively restoring whiteness and balancing color on the display.

First claim

The invention claimed is:

1. An electrophoretic display apparatus, comprising:
an electrophoretic device having a viewing surface;
a drive system coupled to the electrophoretic device for driving the electrophoretic device among a plurality of optical states;
one or more ambient light sensors at the viewing surface of the electrophoretic device for detecting a level of ambient illuminance incident on the viewing surface;
a frontlight unit disposed above the viewing surface of the electrophoretic device for illuminating the viewing surface; and
a frontlight control system coupled to the one or more ambient light sensors and the frontlight unit, and configured to:
(a) receive, from the one or more ambient light sensors, one or more signals indicating a detected level of ambient illuminance incident on the viewing surface of the electrophoretic device;
(b) compare the detected level of ambient illuminance to a predetermined threshold level;
(c) when the detected level of ambient illuminance is less than or equal to the predetermined threshold level, control frontlight illuminance incident on the viewing surface from the frontlight unit to adaptively maintain a constant viewing surface luminance comprising light reflected by the viewing surface from the frontlight illuminance and the ambient illuminance, irrespective of the detected level of the ambient illuminance;
(d) when the detected level of ambient illuminance is greater than the predetermined threshold level, control the frontlight illuminance incident on the viewing surface from the frontlight unit to maintain the viewing surface luminance at generally the same level as a white diffuse reflector under the same detected level of ambient illuminance, wherein the white diffuse reflector comprises a Lambertian reflective surface having a value of L*=100; and
(e) repeat steps (a) through (d) a plurality of times;

wherein the one or more ambient light sensors include at least one trichromatic sensor for detecting ambient trichromatic irradiance in red, green, and blue color channels incident on the viewing surface;
the frontlight unit includes at least one trichromatic light source comprising independently controllable red, green, and blue color channels; and
the frontlight control system is further configured to
(f) receive, from the one or more ambient light sensors, one or more signals indicating a detected level of ambient trichromatic irradiance in the red, green, and blue color channels incident on the viewing surface;
(g) compare the detected level of ambient trichromatic irradiance to a predetermined threshold level in each of the red, green, and blue color channels;
(h) when the detected level of ambient trichromatic irradiance is less than or equal to the predetermined threshold level in any of the red, green, and blue color channels, control the frontlight illuminance incident on the viewing surface from the frontlight unit in that channel to adaptively maintain a constant level of trichromatic irradiance comprising the trichromatic irradiance reflected by the viewing surface from the frontlight illuminance and the ambient trichromatic irradiance, irrespective of the detected level of the ambient trichromatic irradiance;
(i) when the detected level of ambient trichromatic irradiance is greater than the predetermined threshold level in any of the red, green, and blue color channels, control the frontlight illuminance incident on the viewing surface from the frontlight unit in that channel to maintain the viewing surface trichromatic irradiance at generally the same level as an ideal Lambertian reflector under the same detected level of ambient trichromatic irradiance; and
(j) repeat steps (f) through (i) a plurality of times.

2. The electrophoretic display apparatus of claim 1 , wherein the frontlight illuminance incident on the viewing surface from the frontlight unit is controlled in step (c) according to:

E
FL

=

E

AMB
,
min

R
W

-

E
AMB

if
⁢

E
AMB

≤

E

AMB
,
min

where E FL is the illuminance incident on the viewing surface from the frontlight unit, E AMB is the detected level of ambient illuminance incident on the viewing surface, E AMB, MIN is the predetermined threshold level, and R W is the diffuse reflectance factor of the viewing surface in a white state.

3. The electrophoretic display apparatus of claim 1 , wherein the frontlight illuminance incident on the viewing surface from the frontlight unit is controlled in step (d) according to:

E
FL

=

E
AMB

⁢

(

1

R
W

-
1

)

if
⁢

E
AMB

>

E

AMB
,
min

where E FL is the illuminance incident on the viewing surface from the frontlight unit, E AMB is the detected level of ambient illuminance incident on the viewing surface, E AMB, MIN is the predetermined threshold level, and R W is the diffuse reflectance factor of the viewing surface in a white state.

4. The electrophoretic display apparatus of claim 1 , wherein the threshold level is between 3 lx and 500 lx.

5. The electrophoretic display apparatus of claim 1 , wherein the threshold level is about 94 lx.

Assignees

• E Ink Corp

Inventors

• Hertel Dirk

Classifications

• G09G2380/14

  Electronic books and readers · CPC title

• G09G2360/144

  the light being ambient light · CPC title

• G09G2320/062

  Adjustment of illumination source parameters · CPC title

• G09G3/344 Primary

  based on particles moving in a fluid or in a gas, e.g. electrophoretic devices (electrophoretic devices per se G02F1/167) · CPC title

• G09G3/3406 Primary

  Control of illumination source (illumination devices structurally associated with liquid crystal cells G02F1/1336) · CPC title