I know these as LSA's not microlights, but I may well be confusing the terminology.
The terminology is indeed confusing, very confusing. First there was the US'an ultralight as defined per FAA103, with a limited empty weight (254 lb.?) which practically makes it a slow single-seater. Then came European ultralight with 450 kg MTOW, typically a two-seater, initially with a 50-60 hp two-stroke engine, later quasi standardised to the now ubiquitous Rotax 912. Then these birds began to sell in the US too, so the FAA introduced their LSA category, with mostly the same planes but now suddenly with 600 kg MTOW or thereabouts. Then EASA had to follow and created a separate LSA category, broadly akin to the US'an example. Then some European countries introduced an equivalent to the original US'an ultralight, each with their own designation; in the UK it is an SSDR, if my old memory serves. Then some European microlight fliers complained about their 450 kg limit - which is indeed a bit ridiculous, if the exact same plane can fly at 600 kg across the pond - and some countries followed suit. Germany raised the MTOW for an ultralight to 600 kg, France to 500 kg.
Mind you, all of this is sub-icao, so that rules can and do vary from country to country.
To add to the confusion, there is a variance in vocabulary: the (originally) 450 kg plane was called an ultralight in just about every European language, or a local equivalent ("Ultraleicht" in German, "Ultraligeiro" here in PT, &c) but the Brits preferred to call it a microlight, perhaps to avoid confusion with the US'an ultralight.
I think the main difference between LSA and the various kinds of ultralights is that the one has a straight continuation to the PPL, whereas the other is a dead end: an ultralight/microlight license can not be continued into an ICAO PPL. Some of the hours flown may be taken in account, though, again varying per country.
Hoping I have not totally exhausted you
