The diffused natural side light is lacking in the refrigerator box because of the sidewalls that don't allow the natural light to enter from the sides. My Grandmother had an open-topped wooden box around her rhubarb during harvest time, to force the leaves to stretch toward the sun and produce longer edible leaf stems. The stems elongated because of the relative lack of light within the dark colored open box. But the fact that the walls of the refrigerator are white will help considerably with reflected light (mentioned earlier) that comes from above. It will be important to clean the inside surfaces very well so they reflect light as much as possible, rather than absorb light.
Regarding a shadow of natural sunlight caused by the light fixture itself, it would be significant when the refrigerator is situated outside. Unlike any other scenario I can think of, if I had a choice, I would choose a fixture with a small reflector shield in this case, to reduce shadowing. Sunlight is far better and stronger than any artificial light available for us, and the less shadow the better. However, if I had a choice between using a large reflector fixture I already had or buying a new one with a small reflector, I think I'd stay with the one I already own.
I am not understanding, either, why the refrigerator set up would work better in the garage or unheated shed, rather than in the open air. Perhaps Lorn can elaborate.
