Ion-X Glass vs. Sapphire Crystal: Apple Watch Sport brighter, easier to read than Apple Watch

“Is there a visual difference between a watch that uses sapphire versus glass?” Dr. Raymond M. Soneira reports for DisplayMate. “If you were to hold up two identical watches side-by-side, the one with a glass crystal would be about 20 percent brighter than the one with sapphire (due to fundamental principles of optics that reduce its light transmission), so it appears somewhat darker and duller, particularly because the light has to pass through the crystal twice.”

“Minimizing screen reflections is especially important for displays, and sapphire has almost double (191%) the Reflectance of glass,” Soneira reports. “If you are watching a display in total darkness then the screen reflectance doesn’t matter, but it has a surprisingly large effect on every display, even in subdued indoor ambient lighting, and it makes an enormous difference outdoors.”

“We’ll show below how large and how important the reflectance effect is by comparing the display on an Apple Watch that has a Sapphire Crystal to an identical display on an Apple Watch Sport that has Ion-X Glass,” Soneira reports. “The Apple Watch models are perfect for this comparison because they are identical except for their sapphire and glass covers. But they look and perform identically only in the dark…”

Photo of the Apple Watches in 2,000 lux Uniform Ambient Light

Apple Watch Sport with Ion-X glass (left), Apple Watch with sapphire crystal (right) (Source: DisplayMate)
Apple Watch Sport with Ion-X glass (left), Apple Watch with sapphire crystal (right) (Source: DisplayMate)

Much more in the full article – recommended – here.

MacDailyNews Take: We’re loving our Apple Watch Sport models and, after over nine weeks of wearing them 16-18 hours per day, including during sports (running, skating, soccer), there’s not a scratch on either the Ion-X Glass display or the 7000 Series aluminum watch case!


      1. But this is a jewellery crystal, so, naturally, it sparkles/reflects twice more light than glass. This is whole point of emerald, ruby and sapphire, but bad if you use those crystals as display cover.

        With Apple Watch things are additionally complicated because its OLED screen has relatively low maximum brightness due to limitation of OLED and for the purpose of energy saving.

        My guess is that in few years actual contrast ratio under sun will significantly improve; but not now yet.

        1. No, you are wrong. Reflectivity is what you are talking about when what a sapphire does is let more light in and then reflect it back . . . it has more “sparkle” than glass. That’s called refractivity, not reflectivity. Surface reflection can be controlled by adding coatings.

          This whole article is just wrong. I just put my Apple Watch up next to my girlfriend’s Apple Watch Sport. . . and my Apple Watch with a sapphire crystal was brighter and clearer than her Apple Watch Sport with its Ion-X glass. It certainly was not anywhere near as obvious as the photo above, but there was a slight difference with the Apple Watch Sport having a slightly lower brightness, clarity, and quality than the Apple Watch. I suspect a lot of it might be in the brightness setting of the respective watches which would have nothing to do with the crystal installed on the watch.

          1. Refractivity defines angles, not the brightness of reflections, so I am right. (You can shape a glass in certain forms that would provide maximum number of reflections before the light will come back to viewer, but this will still look like a glass, not a true gem due to low reflectivity.)

  1. Something to look at closely under normal light the next time I’m at the Apple store. Holding it in your own hands is always the best way to make a decision.

    1. I got my Italian black rubber Bumper cover from Rome this week before sustaining any scratches on my SG WATCH SPORT. This $35 cover looks fantastic and really gives maximum protection to all but the glass. And Amazon sells protective covers for the glass for only $6.95.
      ArmorSuit MilitaryShield – Apple Watch 42mm Screen Protector.

  2. Gee, I hope MacDailyNews has written permission to reprint the bits of the DisplayMate article. At the top of the article, in red text, it says,

    “Copyright © 1990-2015 by DisplayMate Technologies Corporation. All Rights Reserved.
    This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated into any other work without the prior written permission of DisplayMate Technologies Corporation”

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