LED light source is the best for all the light sources of backlight. The thickness of LED backlight is based on two important factors: the client requirements and the design requirements. Moreover, almost all the clients I have seen choose edge LED backlight. Why? The reason is very simple: it is very thin (1.00～5.00mm) and low power consumption, and the cost of production is only 1/2-1/3 as the bottom LED backlight. But there are some disadvantages for edge LED backlight that it is poor light uniformity and only good for small size. The large size edge LED backlight has a very poor light uniformity, and only the bottom LED backlight can meet the requirement of uniformity of large size light.
The bottom LED backlight that LEDs are at the bottom of PCB and light directly irradiates on the surface of light guide plate is widely used by large-size liquid crystal display (LCD) modules, such as 32 inches and above. The advantage of bottom LED backlight is high illumination and high light uniformity. The structure of bottom LED backlight is more complicated than the structure of edge LED backlight. Usually, it requires a dedicated PCB and a dedicated plastic mold.
Let’s see the bottom LED backlight in picture1. It is very thick, which is 5-10 times thickness as edge LED backlight.
In picture3, it is a close-up of SMD LEDs.
Why there are so many SMD LEDs in bottom backlight? What will happen if it has less SMD LEDs or it is thinner? Some light spots and dark areas will emerge on the surface of the light guide plate.
From the images above, we can see that the bottom light guide plate is a LED lightbox which is very thick and expensive.
By the way, let’s see two special edge LED backlights.
In picture4, edge LED backlight which is composed of the laser-cut light guide plate and printing light guide lattice points adopts DIP LED as the light source.
In picture5, edge LED backlight which is composed of injection molding light guide plate and non-printing light guide lattice points adopts SMD LED as the light source.