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Creating Sunlight-Readable TFT LCD: Methods and Techniques

Increasing Use of TFT Displays in Outdoor Applications:An increasing number of TFT displays are being employed in outdoor applications such as automotive displays, digital signage, and self-service vending machines. The high-brightness conditions in outdoor environments often lead to image fading, resulting in decreased screen readability. The visibility of TFT screens in direct sunlight and the lifespan of LCD displays become crucial factors. HOTDISPLAY has been actively developing sunlight-readable LCD display solutions for many years, demonstrating expertise in this TFT LCD solution.

Understanding Visibility Before Discussing Sunlight Readability:Before delving into how to make LCDs readable in sunlight, let's first understand what visibility entails. Visibility is the ease with which an observer can discern an object, or more scientifically, the relationship between brightness contrast and the human eye's threshold. Therefore, higher contrast of an object leads to better visibility.

What Makes LCDs Readable in Sunlight?To ensure LCDs are highly readable in bright outdoor environments, the brightness of the LCD screen needs to exceed the intensity of light reflected from the display surface. For comfortable viewing by the human eye, the brightness of the LCD should be at least 2.5 times that of its reflected light. Naturally, to make LCDs readable in sunlight, efforts can be focused on either increasing brightness or reducing reflection.


Increasing Brightness for Sunlight Readability of LCDs:

One approach to enhance the readability of LCDs in direct sunlight is by increasing the brightness of the LED backlight. On a sunny day with direct sunlight, the ambient light intensity is approximately 6000 cd/m². A typical TFT LCD with a touchscreen reflects about 14% of the ambient light, approximately 840 cd/m². Currently, many LCD displays use LED backlighting as the light source. Increasing the brightness of the LCD to 800 to 1000 nits to overpower sunlight reflection is feasible. However, this method requires more backlight LEDs and/or higher driving currents. The drawbacks include higher power consumption, increased heat dissipation, larger product dimensions, and a shorter lifespan for the LED backlight. Clearly, boosting backlight brightness is not an optimal solution for making TFT LCDs readable in sunlight.

Using Transflective LCDs:

Transflective TFT LCDs possess both transmissive and reflective characteristics simultaneously. A partial reflective mirror layer is added between the LCD and the backlight. This alteration converts a portion of the reflected ambient light into the light source for the LCD, thereby increasing the brightness of the TFT display. However, transflective TFT LCDs are more expensive than fully transmissive LCDs. Additionally, the partially reflective mirror layer may obstruct some of the LCD backlight, resulting in suboptimal display performance indoors or under low ambient light conditions.


Reducing Reflection for Improved Sunlight Readability of TFT Screens:

What Causes Light Reflection?Light reflects when it encounters the boundary of two transparent mediums. A portion of the light bounces back from the boundary. The amount of reflected light can be calculated using the simplest Fresnel equation:

R = \left( \frac{{n_2 - n_1}}{{n_2 + n_1}} \right)^2

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