Measure Berocca

Take the optic and mark the Berocca tube using felt pen by turning the tube on a flat surface.

Note the yellow paper atop the lens to protect it, which happens to be the same thickness as a diffuser.

Initially I forgot to include the LED mounted on MCPCB (about 1.5mm) when making this measurement but that turned out to be a blessing - it will mean the optic/tube can be sealed below (around the side) rather than having to struggle with trying to get a clean seal on the face of the optic.

See Rob's Homemade LEDs for more about this.