The problem with this is that the ballasts output a high voltage supply to fire the bulbs, and these are often designed with many protection circuits that will all need to be bypassed. It is a bit of an engineering nightmare to go through with this unless you can find a led bulb capable of dissipating/utilizing all the energy at the ballast. Even then, there might be a current sensor or something that may still need to be bypassed. I went through something similar when installing some explosion proof lighting paint booths, so that's why I am quite informed on this matter.