Is it ideal to have the lighting ciruit in a big kitchen around 600watts
in total on a ring circuit like a mains ring or not?

Absolutely not. Your general purpose kitchen ring circuit would preferably
be RCD protected, which would not be appropriate for the lighting circuit.
It would be far better to put it on a lighting circuit. If there is not an
existing circuit with sufficient capacity, then you should install a new
additional circuit.

BTW, 600W is an extremely large amount of wastage. You should consider
redesigning your kitchen lighting replacing grossly inefficient halogen spot
fittings with energy saving types.

Christian.