Summary According DispalyMate survey, the covering shell WatchOLED sapphire crystal display, to achieve two effects: first, to reflective brightness and screen brightness based on the environment; second, better hold onto sapphire surface than ordinary glass. ..
According to the DispalyMate survey report, the sapphire crystal case covered on the Watch OLED display can achieve two effects: first, it can reflect light and adjust the brightness of the screen according to the environment; second, the sapphire surface can better protect the display than ordinary glass. Screen. That is to say, the sapphire glass screen is really scratch-resistant, but the sapphire glass screen watch is more prone to glare than the sports version of the Watch and iPhone. Why is this? 
Sapphire screen Watch reflectance contrast iPhone 6 (picture from displaymate)
In fact, each medium has a refractive index, which is the ratio of the speed of light in a vacuum to the speed of light in the material.
The refractive index of the vacuum is equal to 1, which is 1.5 for a typical glass and 1.77 for a sapphire (the refractive index of most media is between 1-2). Because the refractive index of sapphire glass is much higher than the refractive index of vacuum, when light is emitted from the air to the mirror surface of sapphire crystal, most of the light cannot penetrate the mirror, and when it is reflected to your eyes, it will produce glare. The solution is to use an anti-glare coating, but it is easy to fall off after use, making the surface feel easy to be scratched.
So can you put this coating inside the sapphire? Obviously it doesn't help, because glare is produced by light that cannot penetrate the sapphire mirror. To reduce glare, you must put an anti-glare coating on the surface of the object. The reflections that affect us are the light that is reflected from the surface after it hits the screen of the watch, so there is a place where you need to use the coating.
He said: "Restructuring through a new structure may make it more vulnerable to scratching."
So if you're the one who often uses Watch outdoors, then Watch Sport may be a better choice, even if its screen scratch resistance is not the other two.
Previously, DisplayMate Technologies repeatedly emphasized in the report that the sapphire crystal mirror that Apple uses in Watch will soon be used on smartphones, smart watches and other mobile devices. So, I don’t know how manufacturers who plan to use this material will solve it. What about glare?
Regardless of which solution is used, it seems that it is not the most ideal, and it is caught in a dilemma. In the absence of a solution to the sapphire crystal glare, are you willing to endure for its scratch resistance? Or choose another type of glare that is not so serious, and the scratch resistance is not as strong as sapphire?
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