The widespread use of TFT displays in outdoor applications: More and more TFT displays are being used in outdoor applications such as automotive displays, digital signage, and self-service vending machines. In outdoor environments, high brightness light often causes image fading and reduces screen readability. The readability of TFT displays under direct sunlight and the lifespan of LCD displays have become crucial. HOTDISPLAY has been committed to developing LCD display solutions that are readable under sunlight for many years, and is very familiar with this TFT LCD solution.
Before discussing readability in sunlight, let's first understand what visibility is: before delving into how to make LCDs readable in sunlight, let's first understand what visibility is. Visibility refers to the degree of difficulty an observer can detect an object, or more scientifically, the relationship between brightness contrast and the threshold of the human eye. Therefore, the higher the contrast of an object, the better its visibility.
What makes LCD readable in sunlight? To ensure good readability of LCD in bright outdoor environments, the brightness of the LCD screen needs to exceed the intensity of the light reflected from the display surface. In order to provide a comfortable viewing experience for the human eye, the brightness of an LCD should be at least 2.5 times that of its reflected light. Naturally, in order to make LCD readable in sunlight, we can start from two aspects, namely increasing brightness or reducing reflection.
Increase brightness to make the LCD readable in sunlight:
One way to make LCD more readable in sunlight is to increase the brightness of the LED backlight. On a sunny day with direct sunlight, the ambient brightness is approximately 6000 cd/m2. A typical TFT LCD with a touch screen reflects approximately 14% of ambient light, or about 840 cd/m2. Currently, many LCD displays use LED backlighting as the light source. It is feasible to increase the brightness of the LCD to 800 to 1000 nits to suppress the reflection of sunlight. Therefore, this achieves a TFT LCD that can be read under sunlight.
However, this method requires more backlight LEDs and/or higher driving currents. Disadvantages include high power consumption, increased heat dissipation requirements, increased product size, and shortened lifespan of LED backlighting. Obviously, increasing backlight brightness is not an ideal solution for making TFT LCDs readable in sunlight.
Using a semi transmissive and semi reflective LCD:
The semi transmissive and semi reflective TFT LCD has the characteristics of both transmission and reflection. Added a partially reflective mirror layer between the LCD and backlight. This change converts partially reflected ambient light into the light source of the LCD, increasing the brightness of the TFT display screen. However, the cost of semi transmissive and semi reflective TFT LCD is relatively high. At the same time, the partially reflective mirror layer will block some of the backlight of the LCD, making the display effect of the LCD not ideal in indoor or low brightness ambient light. However, this method is currently the best solution to achieve reading on the display screen regardless of the lighting environment.