Washed IR band pass filter tint off the screen.
I was doing a Surface Book 2 battery replacement. First time doing any actual hardware repair work on a Surface.
It mostly went well, I managed to avoid cracking the screen or ripping any of the cables or antennas. But after reassembly, I noticed the device now has 3 eyes looking at me.
Normal ones should look like below, taken from a Surface Pro 5, note that the IR windows are black and barely visible on the left.
If I read the documentation right, turns out the Windows Hello IR module has a band-pass filter of 810nm applied onto the back of the display glass. The filter is painted or coated on instead of a separate module, it reacts with the alcohol used to clean the adhesive off the glass and is simply dissolved. That’s way my cotton swab turned purple after wiping, I thought it was the adhesive residue, but it’s actually the filter paint.
Any clue on how I search for the raw materials to get them back? Or is it even possible in DIY conditions? Do replacement screen come with working filter paint applied?
I suppose maybe the photography industry or car industry has something similar like IR filter lens or car window tints, but car window tints usually reflects IR instead of letting it pass through. Maybe there is a liquid self-apply variant?
To be honest, this is mostly a cosmetic issue, the Windows Hello facial recognition seem to keep working, however I’m not sure if it remains accurate or robust enough in various lighting conditions.