The requirements governing the marking of general obstructions to aviation such as buildings, power plant chimneys and other obstacles are different to those applicable for wind power. In cities and densely populated areas, objects over 150 metres in height must be identified, while outside such areas the requirement applies to objects over 100 metres in height. In individual cases, such as in areas around airports, lights may also be needed on objects that are 20 metres high and above. For general obstacles, the highest point must be illuminated and the outline of the object to be identified must also be recognisable. On a high-rise block of flats, for example, this would involve the corner points and the roof. If the highest point stands above surrounding objects by more than 45 metres, further lighting levels must be added (e.g. radio masts).
The obstacle lighting must generally not be more than 45 metres away and must be visible from all sides. If this is not possible, additional measures must be taken to ensure that the outline of the object can be recognised. On narrow obstacles (such as wind measuring masts, chimneys, etc.), two obstacle lights must always be used on each lighting level and must be visible from every direction. On tower cranes that revolve upwards, at least 3 lights are needed (on the jib, above the cabin and on the counterweight), while 2 lights are sufficient for tower cranes that revolve downwards.
If the highest point cannot be illuminated for technical reasons, the light must be affixed no more than 15 metres (airport areas 3 m) below it. If an object is more than 100 metres high and an un-illuminated area rises above it by at least 15 metres (airport areas 3 m), hazard lighting with a red intensity of 2,000 cd must be used. This type of lighting may also need to be used to identify particular hazards. Cable-like obstacles such as overhead lines, funiculars, tensioning ropes and similar can be identified with line markers. These ball-shaped markers must, in accordance with German regulations, have a diameter of 0.6 metres and be positioned at intervals of no more than 30 metres.