Current, across a load, develops a voltage. Ohm's law.
White LED luminaries commonly have 3 or 5 watt individual LEDs. A 40 watt ballast, using the former, would require 13 LEDs. Since each individual white LED develops about 3.5 volt, then the series string would develop about 45.5 volts.
Andbefore you ask..... for thermal-induced current balance reasons, no, you cannot place LEDs in parallel.
That is assuming that you could use a current transfomer as a power source, something they are not designed to do.
Lastly, LEDs require DC current, not AC. You would have to rectify it.