Would the BLF Q8 do the job?
The Q8 is a BLF project that is nearing completion. It can run on 1, 2, 3, or 4 Li-ion 18650 batteries. No one can say for sure yet what its final performance ratings will be, but when fully loaded with 4 cells, I suspect that it will be able to bounce 1000 lumens off your ceiling for a minimum of 4 hours straight, and probably a lot longer.
I also like the idea of having a headlamp nearby.