It was a ring flash. Maybe one smaller model of those used in nuclear
fusion experiments. :-)
However, after stopping experiments with ring flashes, I took pictures
without flashes at all. I used a stativ, remote control, very small
f-stop (32 or so) and, to achieve soft lighting conditions, white fabric
as used in beds to achieve indirect illumination using a 2000 W video light.
See picture below:
------- <- white fabric
/
/
/ Vl
/ C
/ P
/
P=plant, C=camera, Vl=video light
Michael