I once had an HP Compaq 6710b. A typical 15 inch business laptop from 2014: A Core2 Duo, 4 GB, thick and reliable. Thin laptops are nice. But I like about thick, older laptops how well they took a fall on a hard object or a hit with a hard object. There used to be a thick plastic cover followed by an even thicker layer of space before the backlight and the actual LCD panel start. Enough room to make all sorts of fun case mods easy.
Those were the laptop screen covers.
So, what I wanted to do is put a piece of transparent plastic in there, engrave something onto it and light is with colouful LEDs from the side to make the engraved lines light up.
This is the type of look that I initially had in mind. The light from the LEDs enters the sheet from the side and becomes visible to somebody viewing from the front, in places where it is refracted by a rough spot.
I removed the cover and used a Dremel-like tool with a thin burr to cut along a line that I had drown on with a felt pen. But before I continued I learned that the way the LCD backlight apparently works is that it not only lights through a diffusor sheet to cover the whole LCD evenly, but also towards the back, where the light gets reflected by a sheet of aluminium back towards the front. So, in order to make the whole light up pink, as I intended, I had to cover the backlight first so the white light from the backlight wouldn't drown out my pink LEDs. I decided to go the easier way and use the white light and forget about my pink LEDs.
The piece that I cut out. (The scrap.)
After I had cut out the hole in the back cover in the shape that I wanted, I put the cover back on the screen to see how the image looks with a whole in the back cover. I couldn't notice any spots or any difference to before whatsoever. So instead of thinking of a way to mount the LEDs and bring a wire up to them, I found a pink piece of transparent plastic (a slim CD case), cut out a piece a bit larger than the hole that I made in the cover, and engraved my picture into that.
White shines the light of the back. Of the light shines back the white shine. Shine of white light shines back the shine. Shine, shine, white light; back of the shine, the shine. Shine shine the shine shine of the back light white shine.
I don't remember exactly why. But additionally to the pink plastic with Pinkie Pie engraved into, I put in a piece of linen-ish cloth. That's where the line structure comes from.
This is how it looks like after glueing both pieces onto the inside of the screen cover and putting the cover back on.
And this is how it looks like turned in, from the view of someboding sitting across of the opened laptop, looking at the back cover of the screen.
I used this laptop for some more time, then gave it away when I got a new one. (I think it was because the keyboard started to fail and I felt it was time for a new one.)
That was the first anything that I engraved into a plastic sheet with the intention to light it. Next in the evolution of me engraving things into sheets of plastic with the intention of lighting them are these LED pictures of My Little Ponies