No at some point the efficacy decreases, I measured the relative efficacy of the LH351D and the peak is at 180mA, under that it decreases : Testing LED efficiency decrease at very low current
So to optimally use this LED one would use PWM dimming under 180mA and analog dimming above.
I haven’t checked other LEDs but it seems that the LH351D reaches its peak at a fairly high current compared to other LEDs which don’t show the decrease at the min current in tests, they should all have this drop though even if the peak is at a lower current.