which photoreceptor cells are functioning as you walk to the bathroom at night when no lights are on?

The photoreceptor cells doing most of the work in that situation are the rods. In very dim conditions with no lights on (called scotopic vision), rod cells are the primary photoreceptors because they are extremely sensitive to low levels of light and can respond to even single photons, allowing you to detect shapes and movement but not color. Cone cells, which mediate color and detailed daytime vision, require much brighter light to function well and are largely ineffective in true darkness, which is why you typically can’t see colors clearly when you walk to the bathroom at night.