If you are an electrician, technician or electrical engineer you will know all about polarity. For those who don’t it is a reference to which way round a circuit is connected to its supply or the way the supply is connected to the circuit or appliance. Most people have an understanding about direct current and alternating current. Typically the current supplied from a battery (of cells) flows in the one direction only whereas the electrical supply to a house (and other places of course) is alternating and essentially flows in both directions, though that is a bit of a theoretical misnomer. Certain things will not work if the current is supplied in the wrong direction, one of those things being diodes. In fact diodes are installed in circuits to ensure current can only flow in the one direction. LED lights or light-emitting diodes are in fact specially constructed diodes which emit photons when a current flows through the device. If the current is presented the wrong way round (wrong polarity) they will not light up. However they can be used if supplied by an alternating current if a bridge rectifier is used. A bridge rectifier is a device constructed with diodes connected in a special way which forces the current to flow in one direction. Here ends the brief electrical lesson but I write it in order to explain my post.
I had installed an LED strip light (resembling a fluorescent lamp) in a house in summer. The lady called me to explain that it had ceased working so naturally I went to investigate. I discovered that the lamp (tube) was indeed at fault as the supply was intact. The supply to the lamp is at one end only, unlike the fluorescent equivalent which is supplied at both ends. That obviously means the tube itself has to be installed the right way round so that the supply can connect to it. Now then, the lighting unit manufacturer has installed the correct colour-coded internal wiring, brown and blue which are live and neutral respectively together with a small fuse. The lamp connector therefore has one brown and one blue conductor connected to it. The end of the tube lamp which plugs into it is marked L and N denoting which terminal connects to each when the lamp is inserted. However when the lamp is inserted so that it shines down into the room the connections end up the wrong way round! That would mean that the lamp supply is the wrong polarity or the wrong way round but in fact it didn’t matter in this case for the lamp worked whichever way it was inserted. That could only mean that a bridge rectifier was in circuit within the lamp’s electronic components. Why then the need to mark the terminals on the lamp L and N? I can only assume it is for information when connecting it to a direct current supply but even that wouldn’t be correct as for a DC supply they would have been marked with the symbols + and -. So why mark the lamp in the first place? I had the lamp replaced under guarantee and it worked just as the other had done. If only the manufacturer had indicated these things in their literature, it would have saved me the time and effort trying to figure it out for myself. The lamp was replaced under guarantee but my time had to be paid for though.