This circuit is used to trigger a camera's electronic shutter circuit when a flash of lightning is present. It has been suggested that this circuit would also work to photograph fireworks displays, I have not tested that out yet, but plan to this summer. The photodarlington should be set up to either look through the camera's viewfinder or a small black tube that gives the same view as the camera's lens. With an SLR camera, this circuit should only be used at night, daytime use will cause it to retrigger indefinitely because the viewfinder goes black then light when the photo is done, this restarts the detector. The photodarlington is a QT semiconductor model QT-L14R1, available from Digi-key. The VN10KM is an N channel mosfet transistor, a more common IRF520 would probably work here, but I have not tried it. Digi-key also sells the VN10KM. If you get any good shots with this circuit, I would love to see them.
Lightning Detector in GIF format (17kb)
Lightning Detector in PostScript format (93kb)
lightning web ring for lots of lightning stuff.
Digi-Key for parts.