Obstructions may be marked, lighted, or both to warn pilots of their presence. There are several different lighting and marking combinations which are used.
Aviation Red Obstruction Lights
Some obstructions use red lights for night time marking and alternating orange and white paint for daytime marking. The red light might burn steady or flash at 20-40 flashes per minute.
Medium Intensity Flashing White Obstruction Lights
This type of obstruction lighting may be used to mark obstructions during the day and night. A sensor automatically reduces the lighting intensity during the night. This type of lighting system is rarely used on a structure less than 200 feet tall.
If the obstruction is 500 feet tall or less, these white lights may be used as the sole method of marking the obstruction. If the structure is taller than 500 feet, however, alternating orange and white paint must be used to supplement daytime visibility.
High Intensity White Obstruction Lights
With this type of obstruction lighting, a sensor turns the obstruction lighting to high intensity during the daytime, medium intensity during twilight, and lower intensity during the night. This type of obstruction lighting may be used as the sole method for marking the obstruction.
Multiple Lighting Systems
Some obstructions are marked with red steady or flashing lights during the night and high intensity white lights during the daytime. This type of obstruction lighting may be used in place of alternating orange and white paint for daytime visibility.
High-Voltage Power Transmission Lines
Medium or high intensity flashing white lights may be used to increase daytime and night time visibility of high voltage power lines and their associated support structures.