Figuring that one Compressor Motor will draw at least 240 Amperes >2 Seconds while starting, there will be a considerable sag in Voltage on this system - especially with small Service Feeders and / or a Transformer which is highly loaded and / or small in KVA size [15-25 KVA].
With Incandescent Lamps, Your Eyes will drammatically notice varying Light Output due to Voltage Sags - even with a drop of 10 VAC, so that's one thing to consider.
I would say the best way to address this is to explain the phenomena to the Client, and leave it up to them [as to simply deal with the dimming or to begin some changes].
Changing to Fluorescent Lamps will reduce the amount of dimming, but not remove the underlying problem of Voltage Sags from the Compressor Motors' high LRA (Locked Rotor Amperage).
This could become a rather intense project!
Scott S.E.T.
