From the sound of it the container probably needs to be pressurized to replicate the conditions of the deep sea or the critters die. If that's the case, opening the container to add food would depressurize it and kill the critters.
Another guess - they would have to be genetically programmed to provide light all the time. I think it might be even more complicated to make them 1st light sensitive then make the sensitivity produce light for the correct condition (when it's light or when it's dark).