What the requirements, for installing GLS
Downlights, in the US?.
We have a whole Code Of Practice, for this,
But in particular, how do you go about installing ELV Dichroic Fittings?.
As with respect to heat dissipation?
Your help please-

http://www.lightswitch.co.uk/help/dichroic.htm

From this I would determine compliance with NEC Article 411. Read the posts here related to this type of installation.

"411.4 Locations Not Permitted.
Lighting systems operating at 30 volts or less shall not be installed (1) where concealed or extended through a building wall, unless using a wiring method specified in Chapter 3, or (2) within 3.0 m (10 ft) of pools, spas, fountains, or similar locations, except as permitted by Article 680."

PS: In the USA, NEC Article 100 defines a "FITTING" as an accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function.