Futurology

Consumer panels are up to 23.5% now, and you can get bifacial cells that can boost that by up to 30%, so up to around 30.55%

Also the light is bouncing around that room, not bouncing off and then back into the sky like it would from the sun, and it's not necessarily all full spectrum, it's the spectrums the plants need, also reducing power compared to what the sun gives it.

Edit: Making shit up now, but what if photosynthesis only needs 30% of the spectrum, and the bifacial panels are 30% it might even be near equal.