Those wearable LEDs spent the last five months sitting on the kitchen window sash, quietly discharging their CR2032 lithium cells:
Occasional voltage measurements produced an interesting graph:
CR2023 primary lithium cells start out around 3.3 V, so these were pretty much dead (from their previous lives in dataloggers) when I slipped them into their holders. The LEDs seem to be blue LEDs, with threshold voltages around 3.6 V, with colored phosphors / filters, so they started out dim and got dimmer. The green(-ish) LED obviously fell over a cliff and went dark in late January; I have no way to measure long-term microamp currents, alas.
The reddish LED is still going, mmm, strong.
If you need a rather dim light for a surprisingly long time, these things will do the trick.
I should gimmick up another astable multivibrator to blink one LED.
The original data: