Actually the drag landing lights create is equivalent to 4 kgs fuel per trip. Multiply that by 204 (the number of aircraft in the EZY fleet) and again by 8 (sectors per day) and again by 364 and you get a fuel saving of 2.4 million kgs per year, not a miniscule amount I think. The lights are of no use in cloud or during daytime during climb or descent, so why waste fuel using them .
Surely anything which makes the a/c more conspicuous when below FL 100 is a bonus - there isn't much fuel saving in having a midair with (for example) a light aircraft?