Listen to the folks above, they are correct in the fact that the 500 W light will probably only draw a maximum of 310 watts at the plug, then allow for losses at the drivers, you will see half of that.
The chinese sellers on E-bay usually tell you what the draw at the plug will be in the fine print and PetFlora can tell you about any losses due to inefficient drivers.
All of the fixtures you see on Amazon can be bought for less on E-bay, especially if you try the make an offer button.
Unless you are going for big dollars, use an E bay LED with other lighting.
My cheap Apollo UFO 180 Watt max (106 actual,) kept my Lemon tree happy last winter but since she is fruiting I am going to need more by next month.