Spot Lights Flicker

[SimpleSimon]

as orig' post. 600watts of halogens not suitable for a 400watt dimmer

But that's to do with the wattage as oppose to the type of bulb.
Think mickey was referring to dimmers that are not compatable with halogens regardless of wattage.

 

[mikeymoo]

other way around (not all dimmers are suitable for halogen lighting)

Resistive
These are designed to control lamps that have a filament, which emits heat and visible light. Typical lamps are standard GLS incandescent, Mains halogen.

Inductive
These dimmers are designed to control light sources which use wire wound components in the form of transformers. An example of this would be low voltage lighting.

 

[Marvo]

I've never come across dimmers that will operate a linear resistive load but won't run an inductive load although there may be a derating factor involved.