For a multi-bulb fixture the LED units do not want to be in the area where high heat is generated as would be the case with incandescent or especially with halogen bulbs.
CFLs have their own special considerations if they are used in situations with special types of lamp dimmers. Such special dimmers may not be compatible with LED lighting modules.
Another consideration comes in from the light quality and perception of what the lighted area looks like. LED lamps have a different light character than do other types of bulbs and mixing them together may be perceived as unpleasant in the extreme cases.
full disclosure here. you may be looking at a product that is similar looking but fundamentally different than what i think it is.
what you are looking at is a bulkhead light for furniture only. meant to be used inside a cabinet box or some other structure that is classed in the NBC as "furniture". even though many places sell these, you cannot legally use these for potlighting where they are submerged into a drywall ceiling, even I have seen these installed so many times in the wrong way. its disturbing. you cannot just cut a hole and clip these into the hole. I have worked on multiple different residences where these have caught fire outright or been smouldering when they were turned off finally.
1) there is no way to connect to the unit in a way that makes the connection compliant with the OEC. the connections have to be in a metal enclosure, and these don't come with it. I have seen every type of disturbingly mis-thought arrangement with these things.
2) the fire code requires that any penetration into the rooms fire barrier (the drywall ceiling) must be in an appropriately fire rated enclosure. since these have a power supply board either onboard or in a little separate module (with a molex connector usually), that part also has to be installed in an approved enclosure.
3) even if you want to do all your connections in an approved rework pot or some other device, they are a weird diameter that doesn't match any pots that I have ever seen.
4) ESA will not pass these in any installation I have ever seen, and I have had inspectors tell me that ESA is still working on getting the legislative clout to have them banned outright, so that they can't be sold at all in Canada without the aforementioned warnings. just remember that you can run electrical cable through a drain line, but its not legal. caveat emptor.
do yourself a favour and get led refit assemblies from cree or greenlite. I buy them by the skid from greenlite for about $15 ea. they are not that much more if you buy just a case of them. they have a 5 year warranty, honoured by a Canadian company, and they are bombproof, commercial grade lights.
http://www.greenlite.ca/en/lights/1895-led-10w-dimmable-retrofit-kit-4-.html
Best Answer
If you want to fight over legalese, you'll be thrilled to know that the courts have ruled in favor of the Oxford comma. The instructions probably predate the court ruling, but after the Court date, the lights should be totally OK in recessed luminaires which are not totally enclosed. Just be aware this has been appealed. If the Supreme Court reverses, your lights will instantly burn out or start a fire.
Seriously, though...
The issue is about cooling. The lamp needs to be cool to function safely. Either:
So all of them depend on either radiant heating (dissipating through the fixture) or convection cooling (air taking away the heat, then moving on through). Radiant heating is often enough for incandescents and HID, and most older fixtures are built only for this. They are not made for the additional cooling required by efficient bulbs.