I made the mistake of painting a flat balck border around my acrylic frame. My thinking was that it would help eliminate some of the IR glow that happens right up close to the LEDs.
BIG MISTAKE!! NO NO NO!!

Because the paint is bonded to the acrylic, the IR light from the LEDs gets absorbed into the black and never even makes it out into the acrylic past the black paint!!
I got NO BLOBS from my acrylic!!

I managed to get the paint off with a solvent that didn’t harm the acrylic.

DO NOT PUT BLACK PAINT ON YOUR ACRYLIC!

thanks for that one, physical borders it is then.

I’ve tried reflective paint it grey in colour and it didnt cause any problems on my test setup… the only thing that kept me away from it, was it was expensive… very expensive.

Taha

This is helpful to know.
I will be making a FTIR set-up next. I thought the same thing with the black paint, and is great to know NOT TO DO IT.
Thanks 4 the tip

Good to know. I saw on DIY somewhere that a guy used black paint, but think it might have just been around the edges where the LEDs are. I wonder if that makes a diffrence?