'tide marks' i should have said. About m descritption of the wavy lines left by the red OHP marker. That's what they were.
Heh thanks for the suggestion here SilverSolder... actually i did not wish to open up this mouse because it seems to be difficult to get into. Only clips. And could wind up breaking those plastic clips.
Just to be clear: my esd matt happens to be color green, and i have small sample of beige. No blue color esd mats here. Although it really should not matter maybe? But I was actually referring to my earlier test with a blue marker pen earlier, that didn't work. So i would not know if a blue ESD mat is any better. Although they are light sky blue. This pen was a dark navy blue. Anyhow we don't usually ever see how inks behave in the non-visible range of the IR spectrum. Because we cannot see it!
But regardless of that, i found a rudimentary 'data sheet' for my exact mouse sensor now. And in that PDF it did say the led is... an HSDL - 4261. So i found that data sheet too.
Heres a link to those datasheets:
https://www.dropbox.com/sh/tvr0m8ewv6of4vi/AAAhkQFJTSNnPEE5Y1VpJZuaa?dl=0Crucially it says that the IR wavelength of the LED is 870nm. In fact it glows very dimly red.
This is useful information!
* Can now look into which wavelengths other mice use too. And compare them. Including for a newer sensor inside of a new mouse, before even purchasing it.
* Can also use the wavelength to look for IR inks to stain the matts with. And find matching wavelength ink. Although for 'red textile dyes' they never say about that. Just different shades / intensities of 'red'
And just like you say:
* Another possible test is to try and replace with a different wavelength LED.
* Sensible thing would be to 1st find the wavelength from other 'known good' mouse models. That other people here claimed works for them
* However it might not work with this specific sensor
Definately worth investigating... At least before buying $80 brand new mouse. Just to even compare the specs at least.