In an unusual step, the U.S. Coast Guard has issued a marine safety alert about the possibility of some LED lighting interfering with communications. The Coast Guard warned that crews, ship owners, inspectors and other mariners have reported poor reception on VHF frequencies used for radiotelephone, digital selective calling (DSC) and automatic identification systems (AIS) when in the vicinity of LED lighting onboard ships. According to the Coast Guard, such LED lighting can include navigation lights, searchlights and floodlights, interior and exterior lights, as well as decorative (adornment) lights.
While LED lighting can work very well for maritime vessels, poorly designed LED lighting systems have been known to cause communication problems. All such lighting should comply with FCC regulations regarding electromagnetic interference. This electromagnetic interference has been known to cause problems with various communication systems.
Radio frequency interference caused by poorly designed LED lamps was found to even create potential safety hazards. The Coast Guard cited the example of the maritime rescue coordination center in one port being unable to contact a ship involved in a
traffic separation scheme incident using VHF radio. That ship also experienced very poor AIS reception.
LED navigation lights have also been shown to degrade signals to VHS receivers including AIS. Also, in some intances, the Coast Guard says that LED lighting installed near VHF antennas has been shown to compound the reception.
For this reason, the Coast Guard suggests that crews, ship owners, inspectors and other mariners test their LED lighting to ensure that it does not interfere in communications.
The U.S. Coast Guard Issued the Following Test Procedures:
- Turn off LED light(s).
- Tune the VHF radio to a quiet channel
(e.g. Ch. 13).
- Adjust the VHF radio’s squelch control until the radio outputs audio noise.
- Re-adjust the VHF radio’s squelch control until the audio noise is quiet, only slightly above the noise threshold. Safety Alert 13-18.
- Turn on the LED light(s).
• If the radio now outputs audio noise, then the LED lights have raised the
noise floor. (Noise floor is generally the amount of interfering signals / static received beyond the specific signal or channel being monitored.)
- If the radio does not output audio noise, then the LED lights have not raised the noise floor.
The Coast Guard noted that if the noise floor is found to have been raised, then it is likely that both shipboard VHF marine radio and AIS reception are being degraded by LED lighting.
To determine the full impact of this interference, the Coast Guard asks that those experiencing this issue to report their experiences to Coast Guard Navigation Center. Then, select “Maritime Telecommunications” on the subject drop-down list, and enter a brief description about the make and model of LED lighting and radios affected, the distance from lighting to antennas and any other information that may help understand the extent of the problem.