This paper was presented at a joint meeting of the Institute and the R.A.F. Specialist Navigation & G.D. Aero-Systems Course Association in London on 21 April 1971, with Group Captain D. F. H. Grocott, C.B.E., A.F.C., in the Chair. At the meeting the paper was illustrated with many slides which greatly facilitated understanding of some passages. Only a proportion can be reproduced here.

Obviously there are many occasions when the navigator would like to retain a full visual capability at night; this is certainly so in the military context where it may be essential that aircraft operations shall be fully effective under night conditions. It is similarly a truism that the acuity of the human eye, that is the ability to resolve fine detail in the image, decreases as night falls and the illumination level is reduced. Because of this there have been many research programmes over the years to develop sensors to extend the capability of the human eye, and one of the most important developments has been the use of low light television (LLTV) systems as an aid to night vision.