Electrowetting display device based on ambient light regulation and control

Abstract

The invention discloses an electrowetting display device based on ambient light regulation and control, which comprises a first light-transmitting upper substrate and a second light-transmitting lower substrate, and an electrowetting display layer is arranged between the upper substrate and the lower substrate; the electrowetting display layer comprises electrowetting display pixel units arranged in an array, and each electrowetting display pixel unit sequentially comprises a common electrode, a second polar fluid, a first non-polar fluid, a hydrophobic insulating layer and a pixel electrode; pixel walls are arranged among the display pixel units; the display device comprises thin film type ambient light sensing units which are arranged on the light emitting side of the pixel wall and correspond to the electrowetting display pixel units in a one-to-one mode. The display device further comprises a diffuse reflection layer and a quantum dot layer. According to the invention, the overall or local gray scale of the display device can be adjusted according to the ambient light intensity, so that the display device is matched with the ambient light intensity, the imaging is clearer, and the display quality is improved.

Description

Technical Field

[0001] The present invention relates to the field of display devices, and in particular to an electrowetting display device based on ambient light regulation. Background Art

[0002] The flexibility of display panels is the main development direction of new display technologies. Electronic paper display technology has the characteristics of ultra-low power consumption and comfortable reading in outdoor light environments. It is one of the ideal carriers of portable and wearable flexible display terminals. Therefore, its flexibility is currently a hot topic in international research. In recent years, electronic paper display devices have attracted much attention due to their advantages such as paper-like appearance, low power consumption, and environmental protection. Compared with electrophoretic electronic paper, electrowetting electronic paper has a faster response speed and can achieve color display. It is an electronic paper display that can achieve high-resolution video playback.

[0003] Electrowetting electronic paper display technology changes the state of pixels by applying voltage between the plates to shrink or spread the ink. The pixel conversion is very rapid and can achieve display. Traditional electrowetting displays rely on reflecting ambient light for display, which results in deviations in the grayscale value of the same ink opening ratio under different ambient light conditions. Especially during the use of electrowetting displays, the user may block the display, causing the local ambient light intensity of the display to be too low, and then the actual grayscale value of the display in this area deviates too much from the ideal grayscale value, reducing the image display quality. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide an electrowetting display device based on ambient light regulation, aiming to adjust the grayscale of the display device as a whole or in part according to the ambient light intensity to match it with the ambient light intensity, thereby making the imaging clearer and improving the display quality.

[0005] To achieve the above-mentioned object, the present invention discloses an electrowetting display device based on ambient light regulation, comprising: a first light-transmitting upper substrate arranged on the light-emitting side of the display device, and a second light-transmitting lower substrate arranged opposite to the first light-transmitting upper substrate; an electrowetting display layer is arranged between the first light-transmitting upper substrate and the second light-transmitting lower substrate;

[0006] The electrowetting display layer includes electrowetting display pixel units arranged in an array, and the electrowetting display pixel units include a common electrode, a second polar fluid, a first non-polar fluid, a hydrophobic insulating layer, and a pixel electrode in order from the light-emitting side downward; a pixel wall is provided between each of the display pixel units to block the cross-flow of the first non-polar fluid;

[0007] The display device includes a thin-film ambient light sensing unit disposed on the light-emitting side of the pixel wall between the electro-wetting display pixels and corresponding to each electro-wetting display pixel unit one by one. The thin-film ambient light sensing unit is used to collect the ambient light intensity. The display device is used to obtain the collected ambient light intensity and control the relative voltage of each pixel electrode with respect to the common electrode to adjust the gray value of the pixel unit by correcting the light-emitting window of the pixel unit for the first non-polar fluid.

[0008] The display device further includes a diffusive reflection layer and a quantum dot layer. The diffusive reflection layer is disposed inside the hydrophobic insulating layer or on a side of the hydrophobic insulating layer away from the light-emitting side. The quantum dot layer is disposed on a side of the diffusive reflection layer close to the light-emitting side.

[0009] Optionally, the diffusive reflection layer is made of a multi-layer porous SiO2 / TiO2 aerogel and is prepared by a sol-gel process.

[0010] Optionally, the display device further includes: a light guide layer, which is disposed adjacent to the diffusive reflection layer and on a side of the quantum dot layer away from the light-emitting side, and is used to focus scattered light onto the quantum dot layer.

[0011] Optionally, the light guide layer corresponds to each electro-wetting display pixel unit one by one, and the light guide layer is embedded in the diffusive reflection layer; the quantum dot layer is a layered structure, and the quantum dot layer is embedded in the hydrophobic insulating layer.

[0012] Optionally, the diffusive reflection layer and the light guide layer of each electro-wetting display pixel unit correspond to each other one by one, and both the diffusive reflection layer and the light guide layer are embedded in the hydrophobic insulating layer. The quantum dot layer is disposed in the second polar fluid, and the second polar fluid contains at least one or a combination of an aqueous solution, a salt solution, an aqueous surfactant solution, an alcohol solution, an ionic liquid, and a polyionic liquid in addition to quantum dots.

[0013] Optionally, the quantum dot layer is grafted onto the diffusive reflection layer as a reflection layer, and the diffusive reflection layer is embedded inside the hydrophobic insulating layer.

[0014] Optionally, the display device further includes: a backlight source, which is disposed on a side of the second light-transmitting substrate facing away from the light-emitting side; and the backlight source excites the quantum dot material to emit light.

[0015] Advantages of the present invention: 1. The display device of the present invention includes a thin-film type ambient light sensing unit disposed on the light-emitting side of the pixel wall between electro-wetting display pixels and corresponding to each electro-wetting display pixel unit one by one. The thin-film type ambient light sensing unit is used to collect the ambient light intensity. The display device is used to obtain the collected ambient light intensity and control the relative voltage of each pixel electrode with respect to the common electrode to adjust the gray value of the pixel unit by regulating the first non-polar fluid for the light-emitting window of the pixel unit. The present invention collects the ambient light (incident light) of the corresponding electro-wetting display pixel through the thin-film type ambient light sensing unit and adjusts the gray value according to the ambient light intensity, ensuring that the gray value of each electro-wetting display pixel matches the corresponding ambient light, thereby realizing local or overall gray adjustment of the display device, and further making the imaging clearer and improving the display quality. Compared with the overall gray adjustment, the adjustment method of the present invention is more flexible and the display quality is higher. 2. The present invention is also provided with a diffuse reflection layer, which generates reflected light with a larger reflection angle for the ambient light, so that the viewing angle of the device is wider. 3. The diffuse reflection layer of the present invention is made of a multi-layer porous SiO2 / TiO2 aerogel and is prepared by a sol-gel process. Compared with the ordinary diffuse reflection layer, the preparation process of the diffuse reflection layer of the present invention is simpler and can accelerate the preparation process of the entire display device. 4. The present invention is also provided with a quantum dot layer, and the narrow-band emission of the quantum dots improves the color purity of the display device and expands the display color gamut. 5. The present invention is also provided with a backlight source, which can enhance the brightness of the display device to make up for the problem of poor reflection imaging quality caused by insufficient ambient light intensity. 6. The present invention is also provided with a light guide layer, which is used to focus the scattered light to the quantum dot layer, and when there is a backlight source, it is used to directionally transmit the backlight source light to the quantum dot layer to ensure the photoluminescence of the quantum dots.

[0016] In summary, the present invention can adjust the gray value of the whole or part of the display device according to the ambient light intensity to make it match the ambient light intensity, thereby making the imaging clearer and improving the display quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of an electro-wetting display device based on ambient light regulation provided by a specific embodiment of the present invention;

[0018] Figure 2 is a schematic structural diagram of an electro-wetting display device based on ambient light regulation provided by the first specific embodiment of the present invention;

[0019] Figure 3 is a schematic structural diagram of an electro-wetting display device based on ambient light regulation provided by the second specific embodiment of the present invention;

[0020] Figure 4It is a schematic structural diagram of an electrowetting display device based on ambient light regulation provided by the third specific embodiment of the present invention. Detailed implementation manners

[0021] The present invention discloses an electrowetting display device based on ambient light regulation. Those skilled in the art can draw on the content herein and appropriately improve technical details to implement it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The device and application of the present invention have been described through preferred embodiments. Relevant personnel can obviously make changes, or appropriate changes and combinations, to the devices and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0022] After research by the applicant, it is found that: the electrowetting electronic paper display technology changes the state of pixels by applying a voltage between the electrodes to make the ink contract or spread, and the pixel conversion is very fast, enabling display. Traditional electrowetting displays rely on reflecting ambient light for display, which leads to deviations in the corresponding displayed gray-scale values for the same ink aperture ratio under different ambient light conditions. Especially during the use of electrowetting displays, it may be blocked by users, resulting in too low local ambient light intensity of the display, and thus the actual gray-scale value of the display in this area deviates too much from the ideal gray-scale value, reducing the imaging display quality. In addition, traditional electrowetting electronic papers rely on the change in the light transmittance of droplets (gray-scale adjustment) after applying a voltage to the device. To achieve the purpose of reflective display, usually through material selection or structural optimization, for example, the reflective function is indirectly realized through components such as a hydrophobic insulating layer and a metal electrode. To improve the brightness of the displayed content and the device contrast, current technological innovations mainly achieve the visible effect by adding a reflective film layer in the device to reflect ambient light. Among them, a metal reflective layer is commonly used, but its specular reflection is significant and the viewing angle is small, so the display effect is poor.

[0023] Therefore, the embodiment of the present invention provides an electrowetting display device based on ambient light regulation, as Figure 1 shown. The display device includes: a first light-transmitting upper substrate 1 provided on the light-emitting side of the display device, and a second light-transmitting lower substrate 2 disposed opposite to the first light-transmitting upper substrate 1; an electrowetting display layer is provided between the first light-transmitting upper substrate 1 and the second light-transmitting lower substrate 2;

[0024] The electrowetting display layer includes electrowetting display pixel units arranged in an array. Each electrowetting display pixel unit successively includes a common electrode 3, a second polar fluid 4, a first non-polar fluid 5, a hydrophobic insulating layer 6, and a pixel electrode 7 from the light-emitting side downwards; pixel walls 8 are provided between the respective display pixel units to block the cross-flow of the first non-polar fluid 5;

[0025] The display device includes a thin-film ambient light sensing unit 9 disposed on the light-emitting side of the pixel wall 8 provided between the electro-wetting display pixels and corresponding to each electro-wetting display pixel unit one by one. The thin-film ambient light sensing unit 9 is used to collect the ambient light intensity. The display device is used to obtain the collected ambient light intensity and control the relative voltage of each pixel electrode 7 with respect to the common electrode 3 to regulate the non-polar fluid 5 to correct the gray value of the pixel unit for the light-emitting window of the pixel unit.

[0026] The display device further includes a diffuse reflection layer 10 and a quantum dot layer 11. The diffuse reflection layer 10 is disposed inside the hydrophobic insulating layer 6 or on the side of the hydrophobic insulating layer 6 away from the light-emitting side, and the quantum dot layer 11 is disposed on the side of the diffuse reflection layer 10 close to the light-emitting side.

[0027] It should be noted that the light-emitting side in the embodiments of the present invention refers to the side facing the user during the use of the display device.

[0028] It is worth mentioning that the thin-film ambient light sensing unit 9 is located on the pixel wall 8, and which electro-wetting display pixel it specifically corresponds to is determined at the time of factory.

[0029] In this specific embodiment, the diffuse reflection layer 10 is made of a multi-layer porous SiO2 / TiO2 aerogel and prepared by a sol-gel process.

[0030] It should be noted that the material of SiO2 / TiO2 aerogel is a multi-layer composite structure, usually composed of alternating or gradient combinations of SiO2 layers and TiO2 layers, and has the characteristics of high porosity and large specific surface area. The diffuse reflection structure enables it to reflect ambient light at multiple angles, thereby increasing the viewing angle of the device.

[0031] Comparing with the patent with the application number 202411617022.2, the preparation of its diffuse reflection layer requires the use of a photoimprinting technique. The sol-gel method in the embodiments of the present invention is more economical and the preparation method is simpler. It is worth mentioning that the reflection angles of different structures of diffuse reflection materials are different. Therefore, in the specific application process, the diffuse reflection material and the structure of the diffuse reflection layer 10 should be determined according to the requirements.

[0032] In this specific embodiment, the display device further includes: a light guide layer 12, which is disposed adjacent to the diffuse reflection layer 10 and on the side of the quantum dot layer 11 away from the light-emitting side, and is used to focus the scattered light to the quantum dot layer 11.

[0033] It should be noted that the light guide layer 12 can focus the scattered light of the diffuse reflection layer 10 to avoid the decrease in the light extraction efficiency of the upper quantum dot layer 11.

[0034] Based on the structure of the light guide layer 12, in the first specific embodiment, as Figure 2As shown, the light guide layer 12 corresponds to each electro-wetting display pixel unit one by one, and the light guide layer 12 is embedded in the diffuse reflection layer 10; the quantum dot layer 11 is a layered structure, and the quantum dot layer 11 is embedded in the hydrophobic insulating layer 6.

[0036] It should be noted that the hydrophobic insulating layer 6 is glass with a fluorosilane (such as perfluorooctyltrichlorosilane) sprayed on its surface. The quantum dot layer 11 is a patterned perovskite quantum dot induced by a femtosecond laser process and embedded in the hydrophobic insulating layer 6. The perovskite quantum dot includes CsPbCl, CsPbBr, and CsPbI, and the quantum dot layer is arranged in an RGB color array (regardless of order).

[0037] It should be noted that Figure 2 The corresponding working states are described as follows:

[0038] Description of the working states of the electronic paper

[0039] When no voltage is applied, the first non-polar fluid 57 with light absorption characteristics spreads on the surface of the hydrophobic insulating layer 661, and the device displays black;

[0040] After applying voltage, the backlight source penetrates the second light-transmitting lower substrate 2, the pixel electrode 7, the diffuse reflection layer 10, and the light guide layer 12, and then excites the quantum dot layer 11 to emit RGB colored light.

[0041] The voltage drives the second polar fluid 4 to squeeze the first non-polar fluid 5 into the corners of the hydrophobic insulating layer 6, adjusting the light-transmitting area.

[0042] The porous diffuse reflection layer 10 scatters the unabsorbed visible light incident from above back to the quantum dot layer 11 for secondary excitation and emission. The independent pixel electrode 7 can adjust the local reflectivity through voltage, cooperate with the ambient light sensing unit (detecting the ambient light brightness and color temperature), and adjust the voltage of each region in real time according to the ambient light intensity, so as to dynamically adjust the reflectivity and the quantum dot light emission intensity.

[0043] Based on the structure of the light guide layer 12, in the second specific embodiment, as Figure 3 shown

[0044] The diffuse reflection layer 10 and the light guide layer 12 of each electro-wetting display pixel unit correspond to each other one by one, and both the diffuse reflection layer 10 and the light guide layer 12 are embedded in the hydrophobic insulating layer 6. The quantum dot layer 11 is disposed in the second polar fluid 4, and the second polar fluid 4 contains at least one or a combination of an aqueous solution, a salt solution, a surfactant aqueous solution, an alcohol solution, an ionic liquid, and a polyionic liquid in addition to the quantum dots.

[0045] Here, the quantum dots are water-soluble quantum dots and alcohol-soluble quantum dots, including but not limited to CdSe / ZnS modified with mercaptoacetic acid dissolved in water, PbS or perovskite quantum dots dissolved in DMF or ethanol, CdS dissolved in water or methanol, etc.

[0046] It should be noted that the second specific embodiment is consistent with the first specific embodiment in terms of the structure of the diffusive reflection layer 10 and the operating state of the device. The main improvement is that the diffusive reflection layer 10 and the light guide layer 12 are embedded in the hydrophobic insulating layer 6. This design will further reduce the incident optical path and increase the reflection effect. And quantum dots are used as the second polar fluid 4, making the manufacturing process simpler and the cost lower.

[0047] In the third specific embodiment, as Figure 4 shown, the quantum dot layer 11 is grafted onto the diffusive reflection layer 10 as a reflection layer, and the diffusive reflection layer 10 is embedded in the hydrophobic insulating layer 6. It should be noted that in the third specific embodiment, on the basis of the second specific embodiment, quantum dots are grafted onto the surface of the diffusive reflection layer 10 as a reflection layer material, and at the same time, the light guide layer 12 is removed. This design is simpler. At the same time, grafting quantum dots onto the surface of the diffusive reflection layer 10 can not only reduce the amount of quantum dots used, but also suppress the self-absorption loss between quantum dots, further improving the light emission efficiency.

[0048] In the first, second, and third specific embodiments, the display device further includes: a backlight 13, which is disposed on the side of the second light-transmitting substrate 2 facing away from the light-emitting side; the backlight 13 is used to excite the quantum dot material to emit light, increasing the display brightness, improving the display chromaticity, and expanding the color gamut.

[0049] It should be noted that the backlight 13 is a blue LED, which is used to excite the quantum dots to emit RGB-colored fluorescence, improving the chromaticity and brightness of the display device. Visible light is not sufficient to excite the quantum dots to emit high-intensity fluorescence, and ultraviolet light may damage the diffusive reflection layer.

[0050] The embodiments of the present invention can adopt a collaborative manner of the backlight 13, the diffusive reflection layer 10, the light guide plate, the quantum dot layer 11, and the light sensor to achieve efficient dynamic full-color display. The adjustment method of the embodiments of the present invention includes that the porous diffusive reflection layer 10 scatters the incident unabsorbed visible light back to the quantum dot layer 11 for secondary excitation and light emission. The independent pixel electrode 7 adjusts the local reflectivity through voltage, and cooperates with the ambient light sensing unit to adjust the voltage of each region in real time according to the ambient light intensity, thereby dynamically adjusting the reflectivity and the quantum dot light emission intensity. Therefore, grayscale and wide-color gamut displays can be performed under natural light of different brightnesses.

[0051] The display device according to the embodiment of the present invention includes a thin-film type ambient light sensing unit 9 disposed on the light-emitting side of a pixel wall 8 between electro-wetting display pixels and corresponding to each electro-wetting display pixel unit one by one. The thin-film type ambient light sensing unit 9 is used to collect the ambient light intensity. The display device is used to obtain the collected ambient light intensity and control the relative voltage of each pixel electrode 7 with respect to the common electrode 3 to adjust the grayscale value of the first non-polar fluid 5 for the light-emitting window of the pixel unit. In the embodiment of the present invention, the thin-film type ambient light sensing unit 9 is used to collect the ambient light (incident light) of the corresponding electro-wetting display pixel, and the grayscale value is adjusted according to the ambient light intensity, ensuring that the grayscale value of each electro-wetting display pixel matches the corresponding ambient light, thereby realizing the grayscale adjustment of the whole or part of the display device, and further making the imaging clearer and improving the display quality. Compared with the overall grayscale control, the control method in the embodiment of the present invention is more flexible and has higher display quality.

[0052] The embodiment of the present invention is further provided with a diffuse reflection layer 10. The diffuse reflection layer 10 generates reflected light with a larger reflection angle for the ambient light, so that the viewing angle of the device is wider.

[0053] The diffuse reflection layer 10 of the embodiment of the present invention is made of a multi-layer porous SiO2 / TiO2 aerogel and is prepared by a sol-gel process. Compared with the ordinary diffuse reflection layer 10, the preparation process of the diffuse reflection layer 10 in the embodiment of the present invention is simpler, which can accelerate the preparation process of the whole display device.

[0054] The embodiment of the present invention is further provided with a quantum dot layer 11. The narrow-band emission of the quantum dots improves the color purity of the display device and expands the display color gamut.

[0055] The embodiment of the present invention is further provided with a backlight 13. The backlight 13 can enhance the brightness of the display device to make up for the problem of poor reflection imaging quality caused by insufficient ambient light intensity.

[0056] The embodiment of the present invention is further provided with a light guide layer 12. The light guide layer 12 is used to focus the scattered light to the quantum dot layer 11. When there is a backlight 13, it is used to directionally transmit the light of the backlight 13 to the quantum dot layer 11 to ensure the photoluminescence of the quantum dots.

[0057] In summary, the embodiment of the present invention can adjust the grayscale of the whole or part of the display device according to the ambient light intensity to match it with the ambient light intensity, thereby making the imaging clearer and improving the display quality.

[0058] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0059] Each embodiment in this specification is described in a related manner. For the identical and similar parts among the embodiments, reference can be made to each other, and the differences between each embodiment and other embodiments are emphasized. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for the relevant parts, reference can be made to the description of the method embodiment.

[0060] The above are only the preferred embodiments of the present invention, and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. An electro-wetting display device based on ambient light regulation, characterized in that, The display device includes: a first light-transmissive upper substrate disposed on the light-emitting side of the display device, and a second light-transmissive lower substrate disposed opposite to the first light-transmissive upper substrate; an electrowetting display layer is disposed between the first light-transmissive upper substrate and the second light-transmissive lower substrate; The electrowetting display layer includes electrowetting display pixel units arranged in an array. Each electrowetting display pixel unit sequentially includes a common electrode, a second polar fluid, a first non-polar fluid, a hydrophobic insulating layer, and a pixel electrode from the light-emitting side downwards; a pixel wall is disposed between the display pixel units to block the cross-flow of the first non-polar fluid; The display device includes a thin-film ambient light sensing unit disposed on the light-emitting side of the pixel wall between the electrowetting display pixels and corresponding to each electrowetting display pixel unit one by one. The thin-film ambient light sensing unit is used to collect the ambient light intensity. The display device is used to obtain the collected ambient light intensity and control the relative voltage of each pixel electrode with respect to the common electrode to adjust the light-emitting window of the first non-polar fluid for the pixel unit to correct the gray value of the pixel unit; The display device further includes a diffuse reflection layer and a quantum dot layer. The diffuse reflection layer is disposed inside the hydrophobic insulating layer or on the side of the hydrophobic insulating layer away from the light-emitting side, and the quantum dot layer is disposed on the side of the diffuse reflection layer close to the light-emitting side.

2. The electro-wetting display device according to claim 1, wherein, The diffuse reflection layer is made of a multi-layer porous SiO2 / TiO2 aerogel and is prepared by a sol-gel process.

3. The electro-wetting display device based on ambient light regulation according to claim 1, characterized in that, The light guide layer corresponds to each electrowetting display pixel unit one by one, and the light guide layer is embedded in the diffuse reflection layer; the quantum dot layer is a layered structure, and the quantum dot layer is embedded in the hydrophobic insulating layer.

4. The electro-wetting display device based on ambient light regulation according to claim 3, characterized in that The diffuse reflection layers of each electrowetting display pixel unit share one light guide layer, and the diffuse reflection layer is embedded in the light guide layer; the quantum dot layer is a layered structure, and the quantum dot layer is embedded in the hydrophobic insulating layer.

5. The electro-wetting display device based on ambient light regulation according to claim 3, characterized in that The diffuse reflection layer and the light guide layer of each electrowetting display pixel unit correspond to each other one by one, and both the diffuse reflection layer and the light guide layer are embedded in the hydrophobic insulating layer. The quantum dot layer is disposed in the second polar fluid, and the second polar fluid contains at least one or a combination of an aqueous solution, a salt solution, a surfactant aqueous solution, an alcohol solution, an ionic liquid, and a polyionic liquid in addition to quantum dots.

6. The electro-wetting display device based on ambient light regulation according to claim 1, wherein The quantum dot layer is grafted on the diffuse reflection layer as a reflection layer, and the diffuse reflection layer is embedded in the hydrophobic insulating layer.

7. The electro-wetting display device based on ambient light regulation according to claim 1, characterized in that, The display device further includes: a backlight source, the backlight source is disposed on the side of the second light-transmissive lower substrate facing away from the light-emitting side; the backlight source is used to excite the quantum dot material to emit light.

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