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.]