Here is an example of the newest recessed LED lighting. There are two shown, one with a wider width than the other. By Juno. It is not cheap, coming in at around $225 US per light. They have heat sinks to keep them cool and each unit has the transformer built in. Why they put a transformer in each one instead of letting people line several lights along one transformer I don’t know.
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The reason each light has its own power supply is because LEDs require regulated current, not voltage. This makes them completely incompatible with standard transformers. The power supply cost is probably small ($5) compared to the enclosure ($30?) and LEDs (a 1W LED currently wholesales for about $8, or about $100 worth in that unit).
So if it costs about $100 for all the parts I’m scratching my head over why they are on sale for $225…..