I’ve got a cracked laptop LCD module by LG, model LP133WF2(SP)(A1) and I am taking it apart to see what’s inside and maybe salvage fun stuff for future projects. After I
failed to learned lessons about salvage the polarizer film, my adventure continues with the backlight module. My ambition is to make it light up again as a diffused light source, hoping it’ll be more pleasant than the point light sources of individual LEDs.
I foresee a decision that I will have to make: do I work with the LEDs directly with its seven-conductor cable? Or do I try to work with the LED driver IC on the board?
But before I get that far, I wanted to examine the physical construction of this laptop LCD backlight. There wasn’t much to it at first glance, just a big flat expanse of white matte material.
I had expected a thin row of LEDs and some sort of light diffuser material, and I saw… just diffuser. The LEDs must be incredibly thin to hide under this black strip which is only about 2mm wide.
I had expected the diffuser material to be a translucent sheet of plastic. When I lifted it away from the frame, I found it’s actually composed of four layers. The top and bottom layers are close to what I had expected, they are translucent but are visibly different from each other. The surprise came in the middle two layers, which had optical properties that reminded me of a Fresnel lens but not in a concentric pattern as usually found in Fresnel lenses.
I’m ignorant on how to characterize this any more specifically, but it feels like an entire discipline of engineering that I have never known before. There are experts out there for this intersection between physics (optics) and manufacturing to mass produce these backlight elements. At some point I hope to learn the technical terms of this material so I can learn more about them. But right now this discovery makes me even more motivated to get the backlight back up and running so I can see this stuff in action. Which means it’s time to read up on that LED driver IC.
[UPDATE: This Hackaday post A Hacker’s Introduction to DIY Light Guide Plates has more details about these backlight layers, as well as making custom plates out of acrylic sheets with a laser cutter.]
2 thoughts on “LG LCD Panel Backlight Also Has Layers”
Apparently, the fresnel / diffraction grating film, in front of the backlight array, is to make the light rays parallel, so as to maximize luminosity while sitting in front of the screen. See an example, here: https://youtu.be/YfvTjQ9MCwY?t=396
Fresnel lenses are cool, but as stated in the post, these sheets did not exhibit the concentric patterns I associate with Fresnel lenses.