A week or so later, our smoke/carbon monoxide alarm went off without apparent reason. We could detect no smoke ourselves, nor could we identify any possible source of CO. It happened again some days later. Odd.
Then Grace was reading a boaters' forum on the web, and came across warnings that LED lights have been known to overheat and burn. Ours were removed straight away...
...and we found much evidence of overheating.
These units were sold as replacements for the bulbs we had. 12 volts. No comments about application. It turns out that the batteries in a boat do not supply a smooth enough current for lights like these. The voltage sometimes rises above 12 volts, and causes them to overheat. There were no warnings on the box about this. They went back to Maplin, and our money was refunded.
We have since bought five LED lights from Bedazzled, who sell LEDs especially for boats. These have circuitry which smooths the voltage they receive, and prevents the overheating. They are more expensive, but the difference is, of course, worth it. We like them, and will soon replace all of the lights on the boat with units from these people. The result will be that we no longer have to keep our lighting to a minimum at nights when we are away from a landline. Any single room in the boat can be lit by all of its lights for less power consumption than just one of the previous lights.
And without the risk of setting fire to the ceiling!