How many watts should flood light be to play basketball at night?

Boys want to play ball at night. Hoop will be about 50 feet away from the light. How many watts should my bulb be? 500 w?
Update: To answer a response:This is just a driveway hoop. Nothing fancy. Just want them to be able to see the hoop. The whole court doesn't need lit up necessarily.
Update 2: Court is concrete: Light will be shown toward the hoop (to the backs of the kids as they play).The court surface is only about 40 ft x 50 ft.
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