Hi there -
I think we might need a bit more information, but maybe I can stillhelp you a bit:
The difference between an observational study and an experiment is that, in observational studies, the researcher makes no attempt to manipulate or change any of the variable. You simply observe the individuals in your study, analyze the data, and draw conclusions. In an experimental study (or just an experiment), you purposely manipulate one of your variables to see how it effects the outcome of the study.
Blinded experiments are experiments where certain data are hidden from the participants and the experimenters in an effort to reduce bias.
So the question is are you manipulating a variable? Well, if you are observing a random sample of people in a cafe, and over time, changing the lighting level (your manipulated variable in this case) to see how if effects the amount of time they stay, then that is an experiment. If you are observing people in cafes of various lighting levels and seeing how long they stay, that's observation.
You can see the short comings of observation (as well as experiments to a lesser extent) when you consider that there are so many other variables (besides lighting) that might effect how long people stay : how hungry they are, their age, their schedule, how much coffee they drank at home, income, etc, etc...