Low Intensity Two colour Approach System Bren, showed green for 'on GP' and red for 'below GP'.
We were taught about it on our aerodrome course (it was still in the 'Air Pilot' too as far as I recall) back in '72, and told the last ones had just been withdrawn. I think it was used as a cheap system on smaller airfields prior to VASIs, which were in turn replaced by PAPIs.