Contactless sensing, using retroreflection of a light beam to sense and measure rotation speed. We wanted black so it wouldn't be as visible as the usual silver

Contactless sensing, using retroreflection of a light beam to sense and measure rotation speed. We wanted black so it wouldn't be as visible as the usual silvery-grey, given it was stuck to the sidewall of black tyres. I keep coming across uses, most recently for tracking research animals in near-darkness (looking down on a floor of scotchlite). The black could be a better choice for that so thanks for the heads-up about it; email me on sfx 'at' tessierlabs.com if you want to know more.