Well it can be a bit of a search for a correct bulb, at reasonable price, and the manufacturers often don't always give very clear info.
I've been looking at LED festoon bulbs to convert a new Perko horizontal mount stern light on my 27 (the small 'dome' type), mounted in the teak trim on the stern. Previous owner had replaced the dome on the original fitting (same style as the Perko) with a all-round one (!), and the light itself was pretty deteriorated. So the bulb is 31mm 'type 71', not the larger, much more common, 42mm. I've found Dr. LED bulbs at $40+ (CAD) (part number 9000173) that are clearly identified as a nav light replacement. Then there is the Victory SourceLED at $16 that is only identified as 'for Perko lights'. I'll probably go for the Dr. LED. At least I found an unused Perko fixture at a marine consignment shop for $22, rather than the $75 I was quoted otherwise. By the way, I looked at the Victory stern lights of the same style. Couldn't find a LED socket-type bulb that would fit. And the Sea Dog versions you find all over the place (which I think would have the same issue with LED bulbs) have not been tested to international standards.
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