Ralph Barone wrote:

Three white LEDs in series probably needs nearly 10-12 V just to overcome
the diode drop. Try just two in series and see if that helps things.

Yes, it might help a little. It turns out (after a short night ride) that
the flicker is most apparent only to someone looking directly at the
LEDs, which operate on alternate half-cycles. An observer seeing the
illuminated field notices much less flicker, though it never goes away
at any speed I can maintain.

Given the complexity of the circuits described in the links Sepp posted
I am very tempted to try living with what I've got. A MOSFET bridge and
peaking capacitor seem like a decent next step if the flicker causes
serious trouble.

Thanks for writing!

bob prohaska