LCD backlight

LCD backlight

First, the backlight module Introduction

BLU (Back Light Module) for the liquid crystal display panel (LCD panel) one of the key components, the liquid crystal itself does not light, the function of the backlight module is to supply sufficient and uniform brightness and light, so that it can properly display the image. LCD panels are now widely used in monitors, notebook computers, digital cameras and projectors and other electronic products with growth potential, it led backlight module and related components demand growth, low in the Panel of the stimulation, and notebook computers and LCD monitors to large-size panels and other needs of the largest growth in demand for the backlight module of the main power source, the backlight module is the second key component of LCD panels.

Second, the backlight module category

In general, the backlight module can be divided into before the light type (Front light) and illuminated (Back light) two, and illuminated the requirements according to their size, to the position of the lamp classification, developed the following three structures :

(1) edge-type (Edge lighting) structure: a light source is placed in the side of the single light source, light guide plate taken no printed design injection molding, commonly used in the following small and medium-size 18-inch backlight module, the side incident light design, with lightweight, thin, narrow box of, low-power features, also mobile phones, personal digital assistant? (PDA), laptop light, There are also large-size led backlight module using side light structure.

(2) direct type (Bottom lighting) structure: large-size backlight, edge-type structure has not the weight, power consumption and brightness of an advantage, it does not contain light guide and light source placed in the structure beneath the epicentral will be carried out. Spontaneous light from the light source (such as lamps, light emitting diodes, etc.) injection after reflection by the reflector, diffuser dispersed upward by a positive after injection, placement of space for larger, use tubes Keyi size TFT panel support up to 2 lamp, but also increases the thickness of the backlight module, weight, power consumption, the advantages of high brightness, good view out the light, the light use efficiency, simple structure and so on, and thus suitable for portability and space requirements less critical of the LCD monitor and LCD TV, its high power (using cold cathode), and poor uniformity of the heat problem caused by LCD still requires improvement, but the current LED backlight has been achieved commercialization.

(3) hollow-type structure: With the increase of image required Chiduo, LCD is also moving in the direction of large size, and now these very large LCD monitors and Bi were used as a hanging television, requires not only the big picture , high brightness and light weight, the appliance also requires high power under low heat effect, the hollow structure in recent years the development of the backlight module, using the hot cathode tube as a light source. This structure is passed to the air medium as a light source, light source and reflected downward by the prism sheet and the reflective plate on the direction of adjustment, the part of the light guide plate and up through the exit on the surface, another part of the cavity by total internal reflection until after re-entering the catadioptric After the role of exit through the light guide plate, and upward or directly into the light guide light emitted or reflected by the effect of a series of re-injection: the shape of the wedge-shaped light guide plate structure, purpose in seeking the effect of homogenization.

Backlight module introduces the key optical components:

Mainly to the LCD panel backlight lcd display module to provide uniform, high brightness light source, the basic principle is the common point or line source, through the simple and effective than high-brightness light body into the surface brightness and uniform light source products. General structure of the cold cathode tube for the use of the linear light source by the reflector into the light guide plate, transforming into a uniform line source distribution of the surface light source, then by all light diffusion film role and the role of the prism film set light to enhance the brightness of the light source uniformity. Here we backlight do a few basic constituent components introduction.

Third, the backlight module consists of:

Backlight LCM includes: a light source (Light Source), LGP (Light Guide Plate), plastic box (Housing), Reflector (Reflector), proliferation of film (Diffuser), Enhancement Film (BEF, prism film), black gum ( Curtain Tape) and so on. As increasingly demanding thinner backlight, so the need to add some iron box (METAL FRAME).

A. Diffuser (Diffuser)
Production Material: PET or PC using the substrate, positive smooth, rough negative

Production methods:

1. In the diffusion layer coated PET substrate (transparent resin mixed light diffusion material)

2. The PC to the substrate, formed by hot embossing roller rough surface

Distinguish methods: PET material when the light through, it will just slightly yellow; PC material as will a bit more blue light passes through.


On the proliferation of film: light to the point of correction; protection prism film.

The diffusion film: the reflective light source evenly spread, covering outlets, appears to prevent the scattering of positive points.
B. prism film (Prism Lens)

Production Material: PET substrate coated covered in jagged or wavy PMMA micro-structure.

Both the upper and lower prism sheet, the difference is the direction of the substrate microstructure (perpendicular) are different.

Role: to enhance the front luminance


BEF Ⅱ — (Rules prism) about 60% increment in one direction, while the two vertical overlap 120% increase
BEF Ⅲ — (irregular prism, to avoid interference) about 59% increment in one direction, while the two vertical overlap 111% increase;

RBEF — but the microstructure of arc-shaped non-right angle, the brightness comparison: BEF Ⅱ> RBEF Comparative Perspective: RBEF> BEF Ⅱ;

DBEF — 3M patented, multi-layer structure by the reflective polarizing film can be attached from each other, can change the direction of light through reflection and then use them.

C. Reflector (Reflector)

Production Material: PET and PC substrates, reflection rate of 90%.

Commonly used PET micro-foam or PC (polycarbonate) filled with TiO2 made. TiO2, etc.
High refractive index (n = 2.62), so the chip in the reflection of light refracted through a very complex way to be reflected back. Instead, PET or PC, etc.

Transparent resin, after a fine foam, foam is only microns in diameter, and the more micro bubbles, the higher the density, the higher the reflectivity. Bulb is the material refractive index of about 1.00, between the foam and the transparent resin to form a good reflective section, which has a higher reflectivity.

Role: reflection of light from the lamp by the incident and scattering effect of light source

D. LGP (Light Guide Panel)
Backlight light source for the conductive medium, the line will be issued by the CCFL light source into surface light source
Material: PMMA — optical acrylic panels, plexiglass that

Characteristics: a low surface roughness and good optical properties

Role: to accept light, to guide the direction of the scattering of light

Type: in order to create the form of points are: printed (by way of screen printing on the proliferation of printed point), non-printed (using the set up lines of touch with the network or production). Non-print type, including mechanical processing, etching and plate replacement and other manufacturing. Divided by the light position: direct type (LGP light in the back), side light type (light source side). The shape points are: rectangular, wedge-shaped, curved and so on.

Screen printing: the use of dry heat or UV inks (light diffusion and reflection properties of material SiO2/TiO2) and printed materials, reflective side of the coating made of outlets in the LGP, LGP destruction of total reflection, so that incident light scattering properties have to form Diffuse positive effect from the LGP uniform injection. The arrangement of type on the grounds sparse network to dense, small to large order.

E. light

Cold cathode fluorescent lamp (CCFL): electron impact at high speed in the high-pressure Hg atom, Hg atom from the unstable state of rapid return to steady state, and the form of energy in the ultraviolet (wavelength 253.7nm) released by the phosphor into visible light absorption.

Role: provide the light source

Lamp cover: focus on the incident light into light guide and heat dissipation. The structure of the lamp cover attached to the metal at the end of white reflective film substrate, the reflective surface of silver or silver attached to increase the reflectivity.

F. Other components

Plastic box: support and protect the internal material

Aluminum: to provide the bottom support, a fixed circuit board


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