Raul Portales Fernandez took (with permission) my my devil stick notation description and translated it into Spanish. How cool is that?
As I was drifting off to sleep, my eyes wandered around the dimly lit room and I noticed how colorless it seemed. Suddenly I wondered what color rods see best, or, put another way (to help people find this page), "what's the frequency response of rods in the human retina?". It took me a while to find the answer, so I record it here to help future researchers get to sleep sooner. (I'd have found it more quickly if I knew to search for "spectral sensitivity" instead of "frequency response", or if I'd just looked on my bookshelf instead of the web.)
Thomas J. Herbert at the University of Miami Department of Biology claims that rods are most sensitive to 510nm (yellow-green) light. Peter Kaiser has a slightly different number (498nm), but shows the whole response curve. (Note that the curves shown are normalized.) From Neuron to Brain, by Nicholls, Martin, and Wallace, which was sitting on my shelf all along, says that the peak absorbance of rods is at 500nm. (These are all fairly close when compared to the cones.)
In addition to answering my original question, I also got to learn the terms "scotopic" (dim light vision, using rods) and "photopic" (bright light vision, using cones). I also learned that rods use the pigment rhodopsin, cones use three flavors of opsin, and that they're genetically very similar, suggesting a common ancestor.
I learned a bunch of other neat things about vision systems, but now it's finally time to sleep.
Fun with photo editing (before and after):