According to ICAO – Annex 14 Medium Intensity Obstruction Lights – Type A, B or C – have to be used where the obstacle is particularly large and the height of the surrounding soil is more than 45m. Medium Intensity Obstacle Lights Type A and C have to be used alone, whereas Medium Intensity Obstacle Lights, Type B, should be used either alone or in combination with Low Intensity Obstacle Lights, Type B.