Here's a heads-up and a question:
I took richms's suggestion of using a cheap PWM dimmer, together with a brick and an LED strip. Interesting exercise.
JCAR Electronics sell a very reasonable strip option - One 3-light segment of an LED strip for $3.60. For experimentation purposes I purchased a strip of 9 lights. It's about 200mm long.
As to the brick, the shop next door (a major lighting chain) had a driver for a very good price - $8.70. The data sheet says it's a 'Eurolite Ultra Series Electronic Transformer'.
That left the 12v dimmer, which cost me $19.20 from JCAR. It's an inline model with a rotary control that's also supposed to be an on\off switch.
I've got these components breadboarded together.
The dimmer's box states 'Dimming 0-100%'. That's not completely accurate - the LEDs never turn off. Very low output, of course, but certainly not '0-100%'. So the on\off part of the gizmo doesn't work.
My question: The transformer's spec sheet also says, 'dimmable with leading edge or trailing edge dimmer'. I take this to mean that the transformer itself is actually dimmable, ie, with the dimmer placed upstream of the transformer, rather than after it, where it's rigged now.
Obviously, I can't use the 12v JCAR dimmer in that situation, but I also have the unused 240v HPM dimmer that I described in my opening post. The model is an 'XL400TWE trailing edge dimmer' and the box says 'suitable for electronic transformers'.
I ask because:
1) It's a better quality dimmer than the JCAR 12v unit and
2) It comes with an on\off switch on the faceplate, something the 12v JCAR dimmer lacks. As I said, its on\off switch doesn't work.