Trying to understand modern downlighters(!)

Typically these push into a c.80mm dia hole cut in the ceiling plasterboard..

There seem to be 2 distinct styles:

A. 12V based on MR16 bulbs usually wired via a separate transformer.

B. 240V based on GU10 bulbs usually wired direct into the mains.

Bulbs may be halogen, LED or CFL.


Q1: How do GU10 LED (240v) (eg screwfix 24524) replacement bulb units work? Inherently, all LEDs are low voltage devices (typically 2V to 4V). Where does the other 236V (ie 240V-4v) disappear to?

(guessing some: sort of electronic voltage dropper as in CFLs - if so, how much heat does that produce? Is it an interference source?)

Q2: MR16 bulbs are also described as GU5.3. Does GU5.3 mean the same as MR16?

Q3: Screwfix list 2 types of tranformer for MR16 (jan catalog p255) cat no 66599 (LED constant current driver) & cat no 85503 (LED constant voltage driver). Which to you use & when?

Q4: How much heat is lost in these transformers?

Q5: Is there a program out there which can be used to design a multi-unit ceiling installation to provide a reasonably even illumination of a worktop h (eg 900mm) off the floor from a ceiling (say) H (eg 2700mm) high? (assuming everything is horizontal & non-reflective).

TIA for any & all help.