Brightness Enhancement Film (BEF)
Brightness Enhancement Film (BEF), also known as a Prism Sheet, is a key component in the backlight module of TFT-LCDs. It is an optical film with precise microstructures that concentrates scattered light from the light source into a forward direction, narrowing the spread to approximately 70 degrees. This makes it an important energy-saving element in LCDs.
A single BEF can typically increase brightness by about 40–60%. When two BEF films are used together with their prism orientations placed at 90 degrees to each other, even higher brightness enhancement can be achieved.
The function of the BEF is to direct light, which would otherwise spread over a wide range of angles, into a narrower, forward-facing angle to increase the intensity of light seen from the front. Essentially, a basic brightness enhancement film is a prism sheet that refracts, reflects, and concentrates light to achieve enhanced brightness.
The drawback of BEF is that, at the same brightness level, the screen appears brighter when viewed directly from the front, but the image becomes dimmer when viewed from an angle.
DBEF (Dual Brightness Enhancement Film)
DBEF (Dual Brightness Enhancement Film) is a reflective polarizer that reflects S-polarized light before it is absorbed by the LCD panel. Through repeated reflections, it allows approximately 40% of the S-polarized light to be reused.
The light emitted from the backlight can be decomposed into P- and S-polarized light, which are orthogonal in polarization direction. DBEF can recycle and reuse the S-polarized light that would otherwise be absorbed by the polarizer, thereby improving the light utilization efficiency of the backlight system.
Compared to BEF, DBEF improves light utilization and increases brightness while overcoming the viewing angle limitations of BEF. Therefore, BEF is sometimes referred to as a “collimating film,” while DBEF is called a “brightness enhancement film.”
BEF and DBEF can be used together to maximize light emission efficiency and to optimize the cost.
Please also refer to the pictures below for the actual products Orient Display made. The right side is with BEF only, the right side is the combination of BEF and DBEF.
If you have any questions, please contact our technical support team.