Well, I had to get up and pee anyhow. It's 1 AM and I'm fairly well dark adapted.
The best led that I have is the Avago green, HLMP-CM30-S000; thanks, James!
I have a bench supply driving the LED through a 1G resistor into my classic Keithley 610C electrometer. I have fairly rotten vision with lots of phosphenes, and nobody really gets dark adapted in San Francisco, but it's definitely making light at 1 nA, with the visual threshold roughly 0.8. Supply voltage at 1 nA is 2.55.
I guess I could move the whole rig into The Cave and wait an hour or so to get really adapted. Or have some ice cream instead.
John