Similar to the sign projects from above, manufacturers mark the surface of the sheet with a pattern of dots, creating escape points for the light to exit along the way. The goal of this plate is to take internally reflected light from the edge and release it in a controlled fashion along the surface such that the front of the screen is evenly lit. This thin fiber optic sheet, called a light guide plate, is illuminated from the screen edge with a bar of LEDs. Separate those layers to find a polarizing layer, a liquid crystal layer, a diffuser layer, clear fiber optic sheet, and finally a thin reflective backing layer. Peel back the inside of a liquid crystal display to find that it actually consists of a sandwich of many layers. It turns out that LCD manufacturers implement a backlighting scheme that uses a similar approach to what we’ve seen so far. It’s because a larger portion of the internally reflected light rays have already exited the plate earlier on. This is the phenomenon that causes the signs to glow.Īt this point you might be able to guess why etched features of the sign become dimmer as they get further from the light source. For glass and plastic, Φc ≈ 42°.īy etching the surface of the plate, we create locations where the internally reflected light rays can scatter and exit the plate at a specific location, rather than reflect back internally. In other words, they will continue to bounce around inside the plate at a fixed angle forever, unless they are interrupted. Light rays hitting the surface at angles greater than or equal to Φc will be totally internally reflected. Light rays hitting the surface boundary at less than Φc will exit the plate immediately at a slightly different exit angle according to Snell’s law. It turns out that there exists special angle Φ c called the critical angle. In this setup, a light source shines from one edge of the plate, sending light rays into the plate at a range of angles. Cutaway side view of an LED light source illuminating an acrylic sheet Let’s start with a cutaway side view of this project where the left side is illuminated by a bar of LEDs. Some fairly simple optics theory behind this hacker project can help us understand what’s going on. To understand that phenomenon, we need a bit of physics. Something that careful observers might point out: image features that are further away from the light source are noticeably dimmer. an acrylic edge-lit display by vipercmd on Instructables. We can take advantage of this quirk to create some pretty swanky looking signage. By etching a pattern on one surface of the acrylic, we create a location where the light is absorbed and emitted, rather than mostly reflected. Much of the light enters at an angle, bouncing back and forth between top-and-bottom surfaces before exiting the other edge. The journey isn’t perfectly straight though. The core concept is that clear acrylic sheets have the ability to act as fiber optics, piping light from one edge to the other. We’ve featured quite a few projects like these on Hackaday, and they’re just the right level of complexity to get your feet wet at the local Hackerspace. Tackling this project made me wonder: how do manufacturers in the electronics industry illuminate those ultra-flat laptop displays and TV screens to get a perfectly uniform glow? Following a bit of internet research, I discovered a treasure trove of useful insights.īefore we dive too deep into how the consumer electronics industry solves this problem, I want to first walk you through an analogous hacker side-project: the laser-cut acrylic edge-lit display. I’ll dig into the some of the working principles, introduce you to my homebrew approach, and leave you with some inspirational source code to go forth and build your own. Today, I’d like to share my findings and introduce you to light guide plates, one of the key building blocks inside of much of today’s backlit screen technology. What I thought would be quick project ended up being a dive down the rabbit hole that yielded some satisfying results. As fate would have it, the crux of this project was finding a way to do just that: to diffuse light coming in from the edges so that it would emit evenly from the front. True to the original, my replica would need to be both slimmed down and backlit with a uniform, natural white glow. Stay tuned for cake at the end of this article. In hyperstylized video game fashion, they were also extremely thin. If you’ve played the game, you’ll remember these signs as the illuminated monoliths that postmarked the start of every test chamber. Last year, I found myself compelled to make a scaled-down replica of the iconic test chamber signs from the video game Portal.
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