Many digital watch screens operate using Liquid Crystal Display (LCD) technology, which allows them to display numbers and symbols by controlling how light passes through different layers.
Understanding LCD Technology
At its heart, an LCD screen, like those found in many digital watches, works by manipulating light using special molecules called liquid crystals.
Based on the core technology: An LCD is produced by encapsulating liquid crystal molecules between a pair of glass substrates equipped with a polarizing filter and electrodes.
The Layers of a Digital Watch LCD
Imagine a digital watch screen as a sandwich of several crucial layers:
- Backlight or Reflector: Most digital watches either have a small light source (backlight) or a reflective surface at the very back to bounce ambient light.
- Polarizing Filter (Rear): This filter aligns light waves traveling in a specific direction.
- Glass Substrate with Electrodes: A thin layer of glass with transparent electrodes etched onto it. These electrodes form the shapes of the numbers or segments you see on the display.
- Liquid Crystal Layer: This layer contains the liquid crystal molecules. Without any voltage applied, these molecules naturally twist light passing through them.
- Glass Substrate with Electrodes (Front): Another layer of glass, often with corresponding electrodes.
- Polarizing Filter (Front): This filter is typically aligned perpendicular to the rear polarizing filter.
How the Display Works
The magic happens when voltage is applied to specific electrodes:
- Light enters from the back (either emitted by a backlight or reflected ambient light) and passes through the first polarizing filter.
- The polarized light then enters the liquid crystal layer.
- Controlling the Display: Text and images are displayed by controlling the switching of voltages and controlling the amount of light transmitted through the polarizers.
- When no voltage is applied to a specific segment (like part of a number), the liquid crystal molecules twist the light passing through them by 90 degrees. This twisted light then aligns with the front polarizer and passes through, making the segment appear clear or the same color as the background.
- When a voltage is applied to the electrodes corresponding to a segment, the liquid crystal molecules in that area untwist or realign. This prevents the light from twisting. When this light reaches the front polarizer (which is perpendicular to the rear one), it is blocked. This blocking of light makes that specific segment appear dark, forming the visible digits.
- The resulting light or dark segments form the numbers and symbols that tell you the time.
By rapidly switching the voltage on and off for different segments, the watch can display changing numbers, like the seconds ticking by.
Example: Displaying the Number "1"
- Electrodes forming the vertical segments of the number "1" receive voltage.
- Liquid crystal molecules in those segments untwist.
- Light is blocked by the front polarizer in those segments.
- Those segments appear dark.
- Electrodes for all other segments (like the horizontal ones that form "0", "2", etc.) receive no voltage.
- Liquid crystal molecules in those segments twist the light.
- Light passes through the front polarizer in those segments.
- Those segments appear clear or match the background.
- Result: You see a dark "1" shape against a lighter background.
This process happens thousands of times per second, allowing the watch to display the time accurately and update it constantly.
