It's a bit heath robinson but 4 of these do the trick fairly cheaply if you can position them in the right places. (I used to put them on top of the fence with my old boy but they shine at eye level and Charlie doesn't like that!) Ideally they need to be a bit higher, shining diagonally down. You can get some on a stand from Screwfix but they're mains only from what I remember. Other manufacturers might do rechargeable ones. You want to find the highest lumens value you can. LAP White LED Rechargeable Work Light 20W 7.4V | LED Worklights | Screwfix.com
There are solar powered ones specifically for arenas but they're expensive. I think Clippersharp do some.