Hi a.d,
what do you mean exactly with "in a dark field manner"?
The pictures are taken in the dark and the flash, triggered at the right moment, is the only light there is. I have set my flash to the lowest power to make the light flash as short as possible. I could try to go for more light, but that means also longer light and perhaps blurry pictures.
Anyway, I ran out of light bulbs at the moment. 
I asked all my colleagues and friends to give all non-working light bulbs to me so should have a new supply soon.