Let's try to smoke it out the other end. iOpener to full!

Hats off to the smallest suction cup we could find! With one good tug, the modestly adhered visible-light filter gives way to reveal the eye of the IR camera.

Because the Constellation sensor's job is to track LEDs that only give off infrared light, any other wavelength is just noise, making it harder for it to operate. This filter blocks out everything but IR, making it easier to pick out the LEDs.

Without the visible light filter, the sensor would see what our fancy IR camera sees—and would have a hard time picking out just the pattern of LEDs to determine the Rift's position and orientation in space.