In article ,
"RichardS" noaccess@invalid writes:

Hmm, that's interesting - are the GU10 mains halogens not generally dichroic
then?

GU10 aren't, and GZ10 are (if I remember the right way round).
You can put the aluminium reflector one in the dichroic lampholder,
but not the other way round. Aluminium reflector lamps have a bevel
around the base, and the dichroic lamps have a square edged base
to stop them fitting in the Aluminium reflector lampholder.

--
Andrew Gabriel