I don't think the bottles not being in a dark area will affect them as the bottles are make of a white plastic and are not clear. API probably recognizes that in an aquarium you will always read a bit of ammonia so their first reading is .05 if it is lighter than that you are within tolerance. It is kind of hooky this way but sensible and to try and mass produce a test kit that will be extremely accurate at a lower level my not be too feasible. I have used other test kits before and they all have there own issues. The one I like from years ago were the marine master test kits, the integers were close together and hard to distinguish apart some time but it was accurate.