48" shop light fluorescent

[spectrum]

hey im new to this in my little grow room and i mean little, i have my plants under a 48" shop light fluorescent with 2 fluorescent lights on them, one is a plant/aquarium light the other is a sun simulator full spectrum, they seem to be growing well with them however my question is if i leave the lights on 24 hours a day, with this speed up there growth or kill them, i thought a plant was like a system, give it twice the light twice the water twice the food and twice the work that they would get fully grown in half the time. or am i just a plant murderer...