The Apple Watch and Apple Watch Edition have sapphire crystal covering their displays, but the lower-cost Apple Watch Sport uses Ion-X glass instead. Both were chosen for durability, but they also reflect different amounts of light. After having previously analyzed the OLED display used in all three watch models, Dr. Raymond Soneira at DisplayMate just published a detailed shootout comparing the display performance of an Apple Watch to an Apple Watch Sport.
While both the watches tested (42mm Apple Watch versus 42mm Apple Watch Sport) use the same OLED screen, they appear different in ambient light, since the sapphire crystal covering the Apple Watch is more reflective than the Ion-X glass on the Apple Watch Sport. DisplayMate measured the reflectance of the Apple Watch Sport to be 4.7 percent, and the Apple Watch was 8.2 percent reflective, a 74 percent increase.
That means the Apple Watch reflects almost twice as much of the surrounding ambient light, making the screen appear less bright. In total darkness, both watches look the same, but once you start adding ambient light, the watch's reflectance quickly starts to affect how bright the display appears, along with its color gamut, saturation, and overall readability. The reflected light competes directly with the light coming from the display, so the display quickly starts to appear washed out.
DisplayMate tested the watches' display performance in a range of lighting conditions, from 500 lux (mid-range indoor ambient lighting) to 2,000 lux (moderate outdoor lighting, or an overcast sky--that's the image at the top of this article, showing the Apple Watch Sport on the right, and the Apple Watch on the left), to 10,000 lux (direct sunlight), and fooled the watches' light sensor to get them up to maximum brightness under all conditions. That showed the contrast ratio decrease sharply as the ambient light increases, but the sapphire Apple Watch decreased faster--the relative contrast ratio of the Apple Watch was 59 percent compared to the Apple Watch Sport. The Apple Watch Sport also showed a better color gamut and less reflectiveness in bright light.
Why this matters: DisplayMate found that Apple had done a great job of minimizing the watches' reflectance by bonding the glass and sapphire to the OLED display without a gap of air, so the reflectance of each model's screen is only slightly higher than the reflectance of glass or sapphire on its own. But the two materials reflect such different amounts of light that if you're planning to use your watch outdoors a lot--to track running workouts or get walking directions, for example--you might want to go for the Apple Watch Sport.