Lumen control signal

What is the signal that controls the Lumen lights?
A normal 1 to 2 mS pulse driving an LED driver will give 1/20 to 2/20 duty cycle so will not go to low or full brightness. I tried it. You must be using something different to eliminate 50 Hz flicker and give full control.
I tagged my question onto the end of this thread:

but had no reply.
My ROV is apart so I cannot measure the signal and I am trying to make a decision on new lights.

I ran my XL4001 LED driver from a pulse generator set at 200 Hz and varied the pulse width from 5 microseconds, which gave a dim light, to 5 milliseconds, which gave maximum intensity.
It appears that BR must be using something like this to get the control of the Lumen lights that is advertised. But the Lumen Quick Start Guide says: “3. Provide a servo PWM pulse from 1100 μs (off) to 1900 μs (brightest)” so the conversion must be in the Lumen itself which appears to be the case.
The Lumen uses an A6211 LED driver which says it needs a 0.1 to 100% duty cycle.
Looking at the schematic of the Lumen I see the PWM signal goes to a microprocessor as SIGNAL_HU and is converted to signal LED-PWM.
To answer my own question: The signal I need cannot be set up on the output on the Pixhawk.