Calibration of Cangaroo II telescope using a fast blue LED light flasher

We describe the results obtained with a light flasher placed on a 10 meter high mound, at a distance of 1.0 km from the Cangaroo II 10 meter gamma ray telescope, giving a light pool of 7 m diameter. The flasher contains an ultrabright blue (λ=460 nm) LED type Nichia (NSPB 510S), which has a temperature stable light output and a risetime of ∼1 ns. The flasher can be operated at 10 ns and 20 ns pulse widths and rates of 30 Hz, 1000 Hz or continuously, from a battery-powered pulse generator to calibrate and test the telescope data acquisition system. The brightness can be controlled by neutral density filters or collimators. The flasher is pointed using a Ramsden eyepiece fitted with cross-hairs.