Revised scale lengths for cometary NH

New values for the Haser model scale lengths of NH are derived from extensive narrow-band photometry of comet P/Halley. The observations require a parent scale length which is 5-10 times larger than previously published values. It is shown that the newly determined scale lengths also give better agreement with recent observations of two other comets: P/Borrelly and Liller. When combined with fluorescence efficiency calculations by others, the present results indicate that NH production in typical comets, relative to that of other molecular species, is about 20 times greater than previously believed.