acrylic glass & infrared light

Two Rows with each four (2x4) Acrylic Glass Panels (75x100x3mm) with different colors.
normal visible light
Two Rows with each four (2x4) Acrylic Glass Panels (75x100x3mm) with different colors. Picture taken with USB-Webcam that has an HI-PASS Infrared Filter mounted. so its a gray-scale-image. some of the -for humans- colorful panels are fully transparent in the infrared wavelength.
only infrared above ~825nm

Is colorful Acrylic glass transparent to Infrared Light?

hover over the image above to find out 🙂

some days ago i bought a breakout-board for the VL53L1X Time Of Flight (TOF) distance sensor. It can measure the distance of an ‘object’ in the range of ~4-400cm.

My plan was to integrate this into the amulet – so the colors can change if somebody comes in view.. just one of the ‘interactive’ ideas..

for this i need some sort of ‘cover glass’ to protect the sensor.
after a short search i found this video of a good solution for cover glass windows.

it describes a method of using two separate windows – one for the transmitter and one for the receiver – with a light-blocking barrier in between. this way the sensor is not fooled by reflections inside the glass..

i want to try and implement this concept.
for the light barrier i want to use black solid acrylic glass – and for the transparent parts i want to use some – to the human eye – very dark color.
so that the ‘sandwich’ of different materials is more of a ‘dark area’.

but for the sensor it should be as clear as possible.
the sensor operates in the ‘near infrared band’ (940 nm).

so i had to find what acrylic glass colors are transparent to infrared.
as i have found no spectral transmission plots / datasheets from the manufacture (i limited my search to Evonik) i just ordered some samples in interesting colors and tested theme myself.

My Results:

seems very transparent:

blocks some amount

milky / translucent (expected as they are for led diffusion…)

  • LED Black & White (7H25)
  • LED Black & White (9H04) SC

so i will likely use the dark blue one 🙂

as Filter for my USB-Webcam i used this IR HIGH pass filter.
it blocks the visible light up to about 825nm. all above is let through.