That is an interesting question. Shadow is everything that is not in direct sunlight (obviously). So maybe you could measure the amount of light in shadow outside? I would not just give it bright light for a few hours and leave it in darkness the rest of the time. That is not the same as standing in shade.
A quick google search tells me, that e.g. in California a bright day of sunshine means a PAR of about 1000 micromoles. But finding a value for shade is much harder. I couldn't find anything useful right now. My guess is, that on a bright day, you might have around PAR 200 in the shade. You can achieve a value like that with some low power LED. Like a marshydro eco 49 with a proper distance to the plants. Keep the light on for 14 hours a day (approx)
You will probably need to do some experimentation yourself on this. Regulate light intensity by moving the lamp closer or further away from the plant. (Or have the lamp fixed and use several plants that stand on different heights)
If you like to do some reading, maybe this will help:
I have only slightly read it right now. It looks like its about photosynthetic reaction in coffee leaves and according PAR values. Should get interesting at page 334