Hello Dear, How can i make 400V, 1000W fluorescent ballast. Which ICs product i use. Could you help me, please. Best Regards, Thank you.

Look at the International Rectifer(Infıneon) Ballast Designer Program, which is highly recommended to use for ballast circuits in great case for long time use and use mainly IR2520D and L6561/L6562D Ic Models.

By the way, for Ballast design over 40W, you should deal with PFC IC/Circuits for more realible and stable in each Grid Voltage Levels.