We took the tandem downtown (rather than a car) to hear an excellent lecture by Jeff Kenworthy on "Disappearing Traffic," part of Vancouver's Bike Month activities. For the trip back, we put the clip-on lights on the tandem, and I discovered something I'd never realized - I couldn't tell what gear we were in. Part of the problem is that the Ergopower shifters don't stay in any one position, like the traditional shift levers. I had put a Shimano "bubble" indicator just above the downtube cable stop, but it was too dark to see it, the front chainring was too dark to check at a glance, and the rear cogs were way back in total darkness.
Normally, when I ride at night, I use my fixed gear "all weather" bike that normally carries lights and fenders. It never occurs to me what gear I'm in at night because I never ride my good bike when it's dark.
I think part of the problem too is that age affects night vision. I find I need reading glasses under normal room lights. Under street lights, the bubble indicator was totally illegible.
The only gear I could recognize was the big cog on back, since that's the limit of shifting. I tried remembering what cog the chain was on, but after a few minutes, you forget. Must be affecting short term memory.