This circuit is a single transistor flyback (Joule Thief) circuit that features a third coil. With it, flash duration and brightness is much enhanced, without resorting to large value capacitors. The performance can be seen in the
following Videos (on Youtube):
The last is meant to upgrade a Solar Garden Light and demonstrates automated daylight power-off - with just an extra diode and resistor.
You can also find more information about this and my other circuits here: