Can ceilihng lights I bought in America be wired to 240volt single phase in Australia?

Yes, but it would surely be cost prohibitive.

Our design point is 120 V / 15 Amp.

The entire circuit and components are designed for that.

To do it for 240, you would basically strip it down to the shell and then rebuild it for 240 V and the amperage used in Australia.
For example, in England the amperage for this type of circuit is 13 amps, if memory serves me correctly.

In the USA, any electrical product must be listed by a third party testing firm, the most popular is Underwriters Laboratories.

You need to check if Australia has the same restriction.

Also, any light fixture purchased in USA for installation in USA is only rated 120 volts.

TK: Codes and certifying bodies aside, an incandescent light socket shouldn't know 120 from 240VAC. I looked at some of the porcelain light bulb bases I have and they are UL approved, rated for "660W, 250V Model 1022". This is in my 120VAC ceiling fan. Could you not use a same thread 240V screw base bulb if such exists? How about the newer LED bulbs rated for 240VAC? I also use a 12V camper bulb in a standard base and it works fine. Your input is valued, Brian

Sure the socket is rated 250 volts, the wire is probably also. Of course a socket will not know 120 from 240 volts.

The issue is the assembly is not rated 240 volts.

My point is while a USA fixture is manufactured with 250 volt parts, it may not be allowed in Australia, and that needs to be checked.

Thanks, Brian