Figure 3 shows how ambient light travels through touch panel and TFT-LCD displays without OCA.
There are air gaps between the two components. This air gap and the difference in refractive index is what causes a loss of transmittance.
The refractive index of air is 1 while the refractive index of a touch panel and polarizer is about 1.5. The reflection at each boundary is 4%, based on the Fresnel Loss calculation. There are three boundaries in this case, therefore 12% ambient light is reflected to the user’s eyes.
Ambient light reflection is considered “noise” to the user’s eyes because it reduces the contrast of the screen. The contrast is 12% worse with this air gap and refractive index difference.
Additionally, 4% light from the display will be reflected out of the user’s view at each boundary. The brightness is 12% incrementally worse with this air gap.
Figure 4 shows how ambient light travels through a touch panel and TFT-LCD display with OCA.
The refractive index of OCA is between 1.4 to 1.5, which is very close to that of the touch panel or polarizer. Based on a Fresnel Loss calculation, the ambient light reflection is almost zero at the boundaries of OCA. There is ambient light reflection of only 4% at the surface of the touch panel.
The light from the LCD travels through OCA with almost no loss. The only light loss is 4% at the surface of the touch panel.
OCA improves screen contrast by 8% and screen brightness by 8%.