night-time film exposures can be shot in as little as 15 seconds (moonlight, clear night) or 20-30 minutes (just starlight) that's not a lot of light, the light at night renders few colors and contains little "usefull" light for plant growth. This perhaps explains the "effect" of night-light has on things; There are a few flowers that only bloom at night, but that is regulated by hormones, not the light directly.