Eight months later, the dead CR2032 cell driving the “ruby” wearable LED has dropped to 2.15 V:
It’s not a true red LED with a 1.5-ish V forward drop, but a white / blue LED with red phosphor or a red filter, with a forward drop well over 3 V.
Against the sunlit backdrop from our kitchen window, the LED looks dark:
Seen in a dim room, it’s still glowing:
The current is now far below the 1 mA/div of my Tek A6302 Hall effect probe, so I have no way to measure the few microamps lighting the junction.
The coarse grid outside the window is a swatch of deer netting we put up during feeder season to keep the birds from killing themselves on the glass.
The Smell of Molten Projects in the Morning 
Help yourself to ANENG 8008 multimeter (or its similar younger brother 8009 with slightly different features) from the usual suspects. For about 20$ delivered you get a 9999 count, true RMS meter with 100uA range. It’s not something you wan’t to poke into mains, but even David Jones didn’t find much wrong with it otherwise.
I have a microammeter around here somewhere, but I’m absolutely sure inserting any series resistance in the circuit would change things enough to invalidate whatever reading I’d get.
If I’d put a current-sense resistor in there originally, I could probably gimmick up a way to measure fractional millivolts, but … maybe next time.
We had to put bird netting up one year when a scrubjay was determined to defend his birdfeeder rights against that intruder in the window. Now, we have suet and the birds are too busy getting suet and seed to notice reflections.