This phenomenon is caused by a combination of optical interference and the working principle of liquid crystal displays (LCDs), and is not actually due to the screen refreshing rapidly or malfunctioning. The main reasons are as follows:
I. Polarized Light + Liquid Crystal "Optical Interference" Effect (The Primary Reason)
1️⃣ Sunlight itself is unpolarized light.
When sunlight shines on the sapphire/mineral crystal dial of a watch, the following occurs:
Reflection
Refraction
Change in polarization direction.
Sapphire crystal, in particular, produces a significant polarization effect on light.
2️⃣ LCD screens rely on polarizers to function.
The basic structure of a liquid crystal display (LCD) is:
Polarizer
Liquid crystal layer
Secondary polarizer
Liquid crystal displays numbers by changing the direction of polarized light.
3️⃣ When the angle of polarized light changes continuously:
Under strong sunlight:
You slightly move your wrist
The angle of sunlight incidence changes
The polarization angle caused by the crystal dial
This causes the light entering the liquid crystal to constantly switch between "matched" and "unmatched" with the polarizer.
The effect you see is: flashing, then dimming, like flickering.
In reality, the screen itself hasn't changed; what changes is "how the light passes through it."
II. The multi-layered reflections of the crystal dial amplify this phenomenon.
Modern watches typically have:
Anti-reflective coating
Multi-layered sapphire structure
These cause:
Slight phase differences
Interference fringes
Local brightness variations
Especially noticeable under sunlight, appearing to the naked eye as a "flash."
III. Not a Refresh Rate Issue (Many people mistakenly believe this)
While LCDs do have a refresh rate:
Typically between 1–60 Hz
It's imperceptible to the naked eye under normal conditions
However:
This flicker only appears in sunlight
It's not noticeable indoors or when the backlight is on
This indicates it's not an electronic problem, but an optical one
IV. When is it most noticeable?
✔ Sapphire crystal dial
✔ Strong direct sunlight
✔ Light-colored background LCD
✔ Low-power reflective LCDs (such as secondary screens in digital watches and smartwatches)
✔ When the wrist or the angle of light changes slowly
V. Is this normal? Will it damage the screen?
✅ Completely normal
✅ Will not damage the screen
❌ Does not indicate aging or quality issues
In fact:
The more "advanced" the crystal and polarization structure,
this phenomenon is actually easier to observe.
Summary
The crystal dial alters the polarization of sunlight, and the LCD screen is extremely sensitive to polarized light. When these two factors are combined, an optical illusion that appears to "flicker" appears under sunlight.