Lyman-alpha emission from the Lyman-alpha forest

It is suggested that high-dispersion long-slit spectra or very narrow-band etalon images of 'blank' sky could reveal patches of Ly-α line emission from the population of clouds whose absorption produces the 'Ly-α forest' in QSO spectra. A non-observation can put limits on the ionizing background at high redshift which are better than those obtainable by direct measurements of background light. (author)