Is there any study to find the plant with the absolute minimum light need?
Let's at first take a set of SHORT DAY PLANTS which are distinguished from the other plants using the photoperiodism parameters. Taking one plant at a time and performing starch detection test by keeping the plant under sunlight may be the only possible way to determine which plant is the most efficient at producing maximum amount of food when kept under sunlight for a particular time. 
If we go deeper into the molecular level, maybe a cross section of the chloroplasts could provide us with the data of number of Photosystem 2 that are present which get activated at 680nm of light and also the number of electron carries like Ubiquinone. Their abundance can determine the quickness of carrying out photosynthesis.
There are even a separate variety of C4 plants that undergo Crassulacean Acid Metabolism also known as CAM plants found in deserts that undergo photosynthesis at night. 

Thus such an experiment would require diverse plants with several parameters to keep in mind and is quite difficult.