1. Overview

Since E-paper is not a transparent display like LCD, it does not require a backlight. Also, due to that the light source of E-paper can only be added to the front, naturally it will be a front light.

2. Principle

The front light uses the reflection of light, and a number of fine particles are made inside the light guide plate through a special process. The light source is transmitted through these particles, and finally the panel emits light evenly. In addition, the light guide plate of different sizes of E-paper need to be customized separately and simple cutting cannot achieve the best result.
For the combination of front light and E-paper, see below:

3. Light bar circuit

1) LED lights connected in series
Series connection of LED lights can ensure that the current flowing through each LED is the same, and the light emitted by this method is even, but the more lights in series, the higher the driving voltage required, and an additional boost circuit is also required.

2) LED lights connected in parallel

Parallel connection of LED lights can ensure that the voltage at both ends of each LED is the same. The light emitted by this method cannot be guaranteed to be uniform. However, due to the parallel connection method, the driving voltage is generally around 3V, which is relatively easier.

3. Light bar circuit

There are generally two methods for tuning the brightness for LED lights:
Method 1: Adjust the driving voltage
Change the brightness of the LED light by changing the voltage at both ends of the LED light strip. The greater the driving voltage, the greater the brightness of the LED light, but the voltage should not exceed the range in the specification, so as not to burn out the LED light .

Method 2: Adjust the driving current
By using the LED light driver chip, the current flowing through the LED light is changed to change the brightness of the LED light. The greater the driving current, the greater the brightness of the LED light, but the current should not exceed the range in the specification , so as not to burn out the LED lights.