In order for your lights to dim the voltage at the service panel must be dropping. This points to some problem with your service equipment or service conductors. The sub panel wiring may be inadequate but that is not what is causing your lights to dim. If all of the connections in your service supply conductors are sound then the utility will have to run larger service conductors to the demarcation point. A licensed electrician could be a big help in convincing the utility that the problem is theirs by certifying to them that the voltage is dropping at the service equipment supply terminals in spite of the connections being properly torqued.
--
Tom
