yes you multiply foot Lamberts by factor if 3.426 to get conversion to Nits.
so 10 FL equates to 34.26 Nits
as per Ted
for projectors you simply use the 10x method to calibrate for HDR. So using the clipping charts (the eggs on the sony UHDs using the 7669 code). You then for instance if say achieving 100 Nits lamp output (29.19 FL) you then with the pattern clip for 1000 Nits.