How much light does CNTL flash "spill" into scene?

At 28mm on a 35mm sensor body, you must be about 3 ft away.  Yes the light is going to show up; it doesn't work by magic.

The system emits visable light.  You now know this, so use it accordingly.

--
--------------------------
Some would have you believe that having to adapt to new technology is a workaround, but having adapted to old technology is photography.