Introduction to the structure of LCD display backlight module
Nov 30, 2022
LCD display backlight module is an important component of LCD display. It's mainly used to provide light for the LCD panel, and usually contains a number of LED lights. In this article, we will introduce you to the structure of the LCD display backlight module.
The following is a typical structure, the actual situation will be more complex, because with the development of technology, each in order to cost or avoid patents, will use different microstructure solutions or combinations of functions, etc., but the main material principle is the same.
First of all, let's look at this sketch, the top is the LCD unit, also called the cell. the bottom of the metal frame plays a protective role, such as the iron frame, but also the plastic frame, etc., to prevent the inside of the optical film from the impact of external forces. According to the optical path to see one by one.
1. Light source
LED light bar. The earliest is the use of CCFL lamps, as the LED lamp technology advances, the brightness increases, more power saving, and other advantages, there is the entire back of the LED lamp design, which is called the "straight down" lamp source. But this design is no longer available.
Figure 2: Straight-down LED light source
Technology has evolved, with the increase in LED luminous power, as well as the invention of 3M brightening film. The emergence of the "side type" light source, is now the third generation.
Figure 3: Side-by-side LED light source (black dashed line is LED light bar)
After the LED light source emits light, the light is directed from the edge of the light guide into the light guide through the masking or reflective material.
2. Light guide panel
The light source of the LED strip shines from the side edge of the light guide into the inside of the light guide, which has a sawtooth-like edge.
When the angle of incidence of light exceeds that critical angle θc, then total reflection occurs. And but if some graphic processing is done on the bottom of the plate to change the angle of incidence and reflection.
3. Reflective film
Most of the light coming out of the light guide goes up, but some of it goes down. This part of the light also needs to be fully utilized, so a reflective film is added underneath to let all the light propagate upward.
The best domestic is also the most expensive is 3M reflective films ESR enhanced mirror reflective film, the reflectivity can reach 98%, and other programs a little lower.
3M's is a nano-thick coating, 1/4 of the wavelength of light. Using optical principles to increase reflection, it is generally about 500 layers, a total of 0.065mm thick. At best, 3M uses this technology for their projectors, which can do more than 700 layers. Now the most common reflective sheet is PET as the substrate, printing, or lamination of the white reflective layer, the main raw material is barium sulfate, or PET on the silver reflective layer.
4. Diffuser sheet
Light from the light guide plate upwards after, including the reflection sheet on the reflection up, into the diffuser.
The diffusion sheet uses the particles on top to make the light have a large diffusion angle through the circular surface of the size particles, and the coating below has an anti-static effect to prevent adsorption with the light guide plate.
In addition, the diffusion sheet can blur the light of the dot above the light guide plate; blur optical defects, so that the light is out evenly; eliminate Newton's ring, and eliminate optical interference stripes.
The function of the upper diffusion is basically to protect the BEF prism film, increase the light angle, etc. so that the light is uniform. All these functions can be integrated into other films.
5. BEF Brightening Film
Light out of the diffusion film, enters the BEF, Brightness Enhanced Film, also called Prism sheet, prism sheet.
The light coming in from the diffusion sheet happens in three ways, one is reflected back, about 50%; the second is through refraction, the light goes up into other optical films such as DBEF; the third is refraction and reflection, etc., into other prism structures, which are used again.
After these light paths of reflection refraction, etc., the light energy will be saved by 40%-70%. This can reduce the demand for LED light source energy, save electricity, environmental protection, enhance the range of electronic products, and other benefits.
6. DBEF
DBEF is Dual Brightness Enhancement Film, which can also call reflective polarization brightening film, this backlight inside, is the highest technical content of the product.
The above is the work of DBEF, the use of a variety of different refractive index materials to form a multilayer film, white light through the DBEF is polarized parallel to the incident surface of the Plight and perpendicular to the incident surface of the S light, P from the German meaning of parallel, S is vertical. DBEF, so back and forth reflection incident, the light energy is fully utilized to achieve the effect of brightening.
