
The number of light units recommended per level depends on the diameter of the structure (D):
D < 6m
3 obstruction lights shall be used (120°)
6m < D < 31m
4 obstruction lights shall used (90°)
D > 31m
6 obstruction lights shall be used (60°)
The number of obstruction lights levels depend on the height of the structure (H):
H < 45m
1 level of low intensity obstruction lights shall be used (see the picture)
45m < H < 108m
2 levels of obstruction lights shall be used: top level with medium intesity, intermediate with low intensity (see the picture)
108m < H < 203m
4 levels shall be used: top with medium intesity, 1st intermediate with low intensity, 2nd intermediate with medium intensity, lower level with low intensity (see the picture)

Light markers (low or medium intensity) should be used on masts, flares and cranes.
The number of light units recommended per level depends on the diameter of the structure:
always
1 obstruction light shall be used on the top (see the picture)
D < 6m
2 obstruction lights shall be used (on diagonally one per corner)
D > 6m
4 obstruction lights shall used (one per corner)
The number of obstruction light levels depend on the height of the structure (H):
H < 45m
1 level of low intensity obstruction lights shall be used (see the picture)
45m < H < 108m
2 levels of obstruction lights shall be used: top level with medium intesity obstruction lights, intermediate level with low intensity obstruction lights (see the picture)