Optical bonding is a process that attaches the touch panel directly to the LCD, filling a small air gap between the front of the display and the back of the touch panel.
The Role of Reflection in Imaging
Reflection of light may be specular, mirror-like, or diffuse, depending on the nature of the interface. Optical bonding helps to reduce the reflection problem. Using the Adhesive whose refractive index is very close to glass and panel (polarizer glass), we can reduce the reflection when light is transmitted through glass and panel.
How Does Reflection Happen?
Optical bonding is mainly dealing with reflection. Now let's look into more detail on how reflection happens and the law of reflection. Reflection is a change in the direction of a wavefront between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound, and water waves.
Reflection of light may be specular (that is, mirror-like) or diffuse (that is, not retaining the image, only the energy) depending on the nature of the interface. When light moves from a medium of a given refractive index n1 into a second medium with refractive index n2, both reflection and refraction of the light may occur.
When the refraction of light waves in water, the dark rectangle represents a pencil sitting in a bowl of water. The light rectangle represents the apparent position of the pencil. Notice that the end (X) looks like (Y), a position that is considerably shallower than (X).
Reflections on smooth still water.
Reflections on wavy water.
Variables Used in the Fresnel Equations
Law of Reflection
It states that the direction of incoming light (the incident ray), and the direction of outgoing light reflected (the reflected ray) make the same angle to the surface normal, thus the angle of incidence equals the angle of reflection; this is commonly stated as θi = θr.
Law of Refraction (Snell's Law)
Snell's law states that the ratio of the sines of the angles of incidence and refraction is equal to the ratio of velocities in the two media, or equivalently to the inverse ratio of the indices of refraction.
How Much Reflection Happens?
The reflection is caused by the difference between the material’s refractive index. The larger the difference, the bigger the reflection happens.
Fresnel equations
When light moves from a medium of a given refractive index n1 into a second medium with refractive index n2, both reflection and refraction of the light may occur.
The fraction of the intensity of incident light that is reflected from the interface is given by the reflection coefficient R.
Calculation of reflection
-
Refractive index
- Vacuum air – 1
- Glass - 1.5
In this case, the reflection coefficient is about 4%.
How Optical Bonding Can Help Reduce Reflection?
Calculation of reflection
-
Refractive index
- Vacuum air – 1
- Glass - 1.5
- Adhesive - 1.474
The reflection between the glass and the adhesive is close to 0%.
Using the Adhesive, whose refractive index is very close to Glass and Panel (polarizer glass), can help reduce the reflection when light is transmitted through glass and panel.
Reduced Reflection Improves Contrast
Now know that optical bonding can help to reduce the reflection. Furthermore, we will show you how the reduction of the reflection and help improve the "extrinsic" contrast ratio and therefore help the outdoor visibility.
- "Brightness" lightens or darkens the image. "Contrast" changes the distinction between the light and dark areas.
- The human eye eventually becomes saturated with brightness and becomes more responsive to contrast.
- Contrast ratio is much more significant than brightness in high ambient illumination environments.
