Not sure about the lumens.
but the ceiling bounce was 280 at startup, and settled at 262 within a few minutes.
I don`t have any lights that I can compare it with, I have the Supbeam and SRK from dx, but both are taken apart.. still waiting on parts.
I wrote down the SRK from DX ceiling bounce lux, and it was 309 at startup. That`s all I have.No idea how many lumens.
My DGQ 26650 NW had a ceiling bounce of 170 on Turbo. (which should be around 1200lumens or so)
SWM D40A and F40A are in the 120-130 ballpark. (both around 900-950 lumens)
So I don`t think it would be a bad guess if I`d say the Ultrafire M51 is around 1900 lumens. (just looking at Djozz graph here)