Regardless of fry or not, I have a 15 watt ceiling bulb on constantly day and night so when the lights go off, it's never pitch black in the 12' X 16' closed room. I learned this when we stayed over at Dorothy Reimer's (the Plant Lady) house. She said it's so as not to startle the fish into doing something like jumping out of the tank or quickly eating the fry when the light come on abruptly.
Z Man