In order for a display to be readable in an environment with very bright ambient light, the brightness of the display (i.e., the intensity of the light emitted by the display) needs to exceed the intensity of the light reflected on the surface of the monitor. In other words, if the intensity of the reflected light is close to the brightness of the display, the contrast of the display will be reduced to the point where the readability of the display is reduced to an unacceptable level. If the total reflectance is high, the display is simply unreadable. To maintain readability, the display brightness needs to exceed the reflected light by a factor of at least 2.5 times.
On a clear day in direct sunlight, with an ambient brightness of about 6000 cd/㎡, the typical reflectivity of a display system including a touch sensor without any special reflection reduction measures is about 14%. This means that the light reflected on such a surface would be 6000 x 0.14 = 780 cd/㎡. A typical consumer display with a brightness of about 350 cd/m 2 would not be readable under these conditions.
One solution is to increase the display brightness above 2000 cd/㎡ . While theoretically possible, this would require more backlight LEDs (or other light sources) and/or higher drive currents, resulting in high power consumption, excessive heat dissipation, increased size, and shorter lifespan. This is unacceptable for mobile devices, but even for stationary applications or in-vehicle displays, display brightness is typically limited to 1000 cd/㎡ for the reasons mentioned above.
Another way to make these displays sunlight readable is to reduce their reflectivity to a level that ensures that the intensity of reflected light is significantly lower than the display brightness. Reducing the surface reflectivity alone is not enough, because incident light is not only reflected on the top surface. An underlay of different materials also contributes to total reflection, as light is also reflected at the interface of two different materials with different refractive indices. Therefore, adding a touch sensor to the display increases the total reflectivity of the system.
As noted above, the total reflectivity of a touch display system without any reflection reduction measures is approximately 14 per cent. Such a system consists of three glass/air interfaces: the top surface covering the lens, the bottom surface of the sensor, and the top surface of the display, each of which contributes about 4.5 per cent to the total reflectivity. There are also a number of internal interfaces, however, these do not add significantly to the total reflectivity because the refractive indices of the materials that make up these layers (glass, ITO, adhesive) are very similar to each other. Therefore, measures to reduce reflectivity are focussed on the glass/air interface.
Methods for reducing reflectance: Reducing the reflectance of the top surface by a transparency enhancement film or coating
This can be achieved by applying a transparency enhancement film or a laminated transparency enhancement film or any other coating with transparency enhancement properties such as AR coatings. The final top reflectance can be reduced to a value between 1% and 2.5%, depending on the type of film used or, in the case of a transmittance-enhancing film, on the number of layers applied to the surface. As one would expect, the lower the reflectivity value of the film or coating, the higher its cost.
Anti-reflective touchscreens are increasingly being used in reading devices, especially in outdoor or high light environments, such as libraries, outdoor billboards, and e-book readers. By integrating anti-reflective technology, these devices significantly improve the readability and visual comfort of the screen under strong light.
Specific applications include but are not limited to:
1. Touch screen readers: In libraries, community centres and other institutions, touch screen readers make use of anti-reflective touch screen technology to enable readers to easily read e-newspapers even in bright environments, reducing reading barriers caused by light reflection.
2. E-book readers: modern e-book readers commonly use anti-reflective screens to ensure that users can enjoy a comfortable reading experience in outdoor sunlight, while reducing eye fatigue.
3. Education Tablet: In the field of education, anti-reflective touch screen tablets are widely used in multimedia teaching to ensure that students can clearly see the screen content in classroom environments with large changes in light.
Anti-reflective touch screen in reading devices show the following significant advantages:
1. Enhance readability: In a bright light environment, anti-reflective touch screen can significantly reduce the reflected light on the surface of the screen, improve the contrast of the screen, so that the text, pictures and other content is more clearly visible.
2. Enhance visual comfort: Reduce the stimulation of reflected light to the eyes, reduce visual fatigue, so that users can read comfortably for a longer time.
3. Expand application scenarios: Due to its excellent performance in bright light environments, the anti-reflective touch screen enables the reading device to be used in more outdoor or high light situations.
4. Enhance user experience: By improving the screen display and reading experience, anti-reflective touch panels enhance user satisfaction and loyalty to the reading device.
In summary, the application of anti-reflective touch screen in reading devices not only improves the practicality and functionality of the device, but also brings users a more comfortable and convenient reading experience.
