HLG has similar gamma characteristics to SDR in dark range (processing in blacks similar to BT.709 below 100 nits), then changes to a log gamma above ~14 nits.

Extends log processing of displays high brightness peaks up to 2.5 to 3 stops to mitigate blown-out or clipped whites.
These LUT variants offer support for both “narrow range” and “full range” PQ signals, as well as options that allow BT.2100 colour primaries to be used with hardware LUTs that usually assume BT.709 colour.